JPH0926663A - Image forming device - Google Patents

Abstract

(57) [Abstract] (Correction) [Problem] In the production of a color reproduction image, the gradation adjustment and the color adjustment, which were difficult with the prior art, are integrated (merged).
Provided is an image forming apparatus incorporating a new color separation technology. An image for producing a halftone (halftone) color duplicate image on a desired image expression medium by gradation conversion of image information of a continuous gradation color original image by a gradation conversion unit of an image forming apparatus. In the forming device, the gradation conversion part, which is the core component of the forming device, can be used for color separation by integrating both gradation and color tone by using a specific <gradation conversion formula>. It is possible to efficiently produce a high-quality color reproduction image in which the color tone is adjusted as well as the color tone.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention converts halftone (hereinafter referred to as halftone or halftone dot gradation) by gradation conversion of image information obtained by photoelectrically scanning a continuous gradation color original image. ), An image forming apparatus for producing a color reproduction image.

In particular, the present invention relates to an image forming apparatus in which a gradation converting section, which is a core component of the image forming apparatus, has a new function. More specifically, the gradation conversion unit of the image forming apparatus of the present invention does not use the conventional density information value as the image information of the color original image, but the characteristic curve of the recording medium on which the color original image is recorded ( In addition to using the light intensity value to eliminate the influence of the light intensity value incident on the recording medium and the characteristic curve defined by the density value formed on the recording medium, a color original document is created using a specific gradation conversion formula. It is characterized in that it has a function of converting the light amount value of an image by gradation conversion and at the same time adjusting the color tone. The image forming apparatus of the present invention quantitatively determines not only the gradation (also called density gradation or gradation) but also the color tone (color tone).
The present invention provides a high-value-added image forming apparatus that can be controlled rationally and that integrates gradation and color tone adjustment.

The present invention relates to an image forming apparatus incorporating a new gradation conversion technique in which gradation and color tone controls are integrated as described above. However, in the following description of the present invention, the gradation conversion unit of the image forming apparatus of the present invention is new in the sense that the adjustment of the color tone at the time of gradation conversion, which has been difficult in the prior art, is rationalized and quantified. The emphasis is on having a color tone management adjustment function.

[0004]

2. Description of the Related Art As is well known, a print image, a copy image (copy image), a printer output image, a TV (video) image, and the like are printed from a color original image recorded on various recording media by various color reproduction techniques. Various color reproduction images have been produced. In the production of these color reproduction images, firstly, the density gradation (gradation) and color tone (color tone) of the color original image are Hi-Fi color (High-Fidelity, high fidelity color) on the color reproduction image. It is a very important subject to reproduce by the second, and secondly, to adjust to a tone having a desired tone (including both tone and color tone).

However, in the conventional technology, it is the current situation that the above-mentioned problems cannot be reasonably carried out with work regularity. This is a technique for faithfully reproducing the tone (gradation and color tone) of the color original image on the color reproduction image, and further for adjusting (correcting or changing) the tone of the color original image to a desired tone. , A non-linear conversion processing technique for converting image information of a color original image which is the basis thereof, particularly image information in a density region into half tone gradation (hereinafter referred to as image gradation conversion technology or image gradation conversion method). .)
This is because it does not support rational theory, and performs image gradation conversion irrationally and irrationally, relying largely on human experience and intuition.

The above-mentioned points will be described below in the field of the technology for producing a color print image to which the present invention is related and which is always required to have high quality. In the prior art, when a color print image that is a duplicate image is produced from a color film original (about 90% of the color film original is a transmissive type or a transmissive type), the brightest part of the color film original is produced. There is no intention to rationally grasp the density characteristics from the (H part) to the darkest part (S part), and further, there is a continuous tone color film original image and a halftone dot color print image which is a duplicate image. It can be said that the setting of the "color separation curve (also called the color separation work characteristic curve, halftone dot characteristic curve, etc.)" that determines the correlation completely depends on human experience and intuition.

Generally, in the production of a color print image, a color film original image (hereinafter, simply referred to as a color original image) is color-separated by a color scanner, and a multicolor plate making (generally C plate, M plate). Edition, Y
The four editions, the edition and the BL edition, are considered as one set. ) Is performed to reproduce a halftone dot color print image. As is well known, the C plate (cyan), the M plate (magenta), and the Y plate (yellow) are color-reduced corresponding to R (red), G (green), and B (blue) of the additive method. It has a complementary color relationship according to the law, and the BL plate is called black or black plate.

Although the above-described color scanner is a mechatronics-type extremely expensive device, one of the major problems in the industry is that its operating rate is extremely low at about 30% on average. . The main reason why expensive color scanners and the like have such low operation rates is that the setup time for operating the color scanner (scan
Since the ner setup time is long and the quality of the product obtained by color separation work is unstable and insufficient, rescan (re
There are many scans and remakes.

Considering this from a slightly technical point of view, as described above, as a tool for color separation work, although a color scanner or the like which is highly sophisticated and expensive at first glance is used, Multiple elemental technologies for disassembly work, such as color reproduction, color correction, and color correction (Color Reproduc
technology and density gradation (Gradat
It can be said that the ion () conversion technology is not systematically organized, which is the main reason for the low availability of color scanners.

As is well known, the masking equation (Ma
sking equation) and Neugebauer equation (Neugebauer
has been pursued scientifically by applying equations). However, the latter technique of converting the density gradation of the image (this is attributed to the problem of what size halftone dots should be set for all pixels in the color original image).
Has been left unchecked without rational theoretical support, and this part is largely dependent on human experience and intuition.

Since various devices for color separation have been developed under such a condition, from the viewpoint of practicing color separation under the unified adjustment of color tone and gradation, the device itself In addition to being undeveloped in the basic design technology of, the operator's guessing work and the operator's experience and intuition are eliminated while using an expensive electronic color separation device (color scanner) that is expensive in actual work. Can't do (withou
t operator evalution, without operator's guess wor
k), it is not always possible to produce stable high-quality color print images.

Particularly, when the color original image is not a standard original produced under appropriate shooting and exposure conditions and appropriate development conditions, for example, an overexposed overbright original, an underexposed overexposed original, a high key or low key Manuscript,
Furthermore, if the original is a non-standard original such as an original with color cast or a faded original,
Color separation work cannot be carried out reasonably and efficiently. That is, it is impossible to rationally perform color separation work on these non-standard color original images, and there are problems such as the low operation rate of the color scanner, the instability of the product quality, and the increase in the rescan rate. I have.

[0013]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present inventors not only faithfully reproduce the image quality of a color original image (the quality evaluated by both the gradation and the color tone), but further proceed to the above. In order to rationally produce a halftone gradation color reproduction image having a desired tone (gradation and color tone) from various color original images, prior to improvement of color reproduction and color correction (correction) technology. We have a basic recognition that the technology for converting the density gradation of each pixel of a color original image must be rationalized.

Based on the basic recognition by the present inventors, the present inventors previously proposed a method for rationally converting the gradation of a color original image based on a novel gradation conversion formula. And achieved certain results (for example, Japanese Patent Application No. 63-114599, U.
SP4, 924, 323; Japanese Patent Application No. 1-135825
No., USP 5,313,310; Japanese Patent Application No. 1-2121.
No. 18, USP 5,057,931; Japanese Patent Application No. 3-78.
668, USP 5,134,494, etc.).

Since the novel gradation conversion method proposed by the present inventor has a deep relationship with the gradation conversion method applied to the image forming apparatus of the present invention, the outline of the gradation conversion method will be described here. Will be explained. The gradation conversion method applied to the present invention is
Although it is a further improvement based on the gradation conversion method, such an improvement is an essential technical constitution of the present invention.

In the prior art, color separation of a color original image is performed by literally separating an original image (subject, entity image, actual image).
A scene is the apple itself if the subject is an apple. ) To a "recording medium" called a photographic light-sensitive material (photographic light-sensitive emulsion) under a predetermined exposure condition (as is well known, the intensity I of the incident light and the incident time t are E, the exposure amount E is E = It.) Based on the density information of the color photographic image recorded (the color separation operation includes both reproduction of gradation and reproduction of color tone as described above). I am doing it. As is well known, photographic density (photographic d
ensity) is formed, and this becomes a medium image. The curve showing the correlation between the above-mentioned photographic density (blackening degree) and the exposure amount E of the photographic light-sensitive material is a photographic density characteristic curve. This is the photographic density (D) on the vertical axis (D = logIo /
I) and the horizontal axis is the logarithmic value (logE) of the exposure amount E and is displayed. For a film or a dry plate (transparent original), the ratio of the intensity I of transmitted light to the intensity Io of incident light is
It goes without saying that the ratio of the intensity I of reflected light to the intensity Io of completely reflected light is used for printing paper (reflection original).

The above-mentioned photographic density characteristic curve (hereinafter, simply referred to as "density characteristic curve") is typically a downwardly convex foot portion, a substantially straight linear portion (linear intermediate portion), and an upward convex shape. Is a complex curve with shoulders (see FIG. 1 below for this point). In the prior art, the color separation work is performed based on the density information value of each pixel of the color original image. In other words, the conventional color separation technology is constructed from the standpoint of the vertical axis (density value) of the density characteristic curve. The image information value (density information value) of the color original image (medium image), which is the basis of the color separation work in the related art, is not proportional to the image information value of the original image (entity image, subject, actual scene). It is greatly influenced by the light-sensitive characteristics (density characteristic curve) of the photographic light-sensitive material (photographic light-sensitive emulsion) which is a recording medium. That is, the photographic density of the color original image which is a medium image is linearly related (the linear relationship of 45 ° of 1: 1) to the exposure amount (logarithmic value) which is the image information value from the subject (substantial image, real scene). Not what I did. It is well known that the discrimination characteristic of light and darkness in human vision is logarithmic, and humans can determine the amount of light incident on the visual system from a subject (substantial image) based on the discrimination characteristic described above. I am evaluating. Here, the gradient of concentration change is linear
I feel something that is natural.

As is clear from the above description, in the production of a color print image, when the color separation work is carried out by using the density value (D = logIo / I) of the medium image recorded on the photographic light-sensitive material as a clue, it becomes Since the density information value after being affected by the photosensitivity of the photosensitivity material is used, the image information value (light intensity value) obtained from the subject (real image, real scene) that is the true target of duplication is used. It's not what you're doing. Based on the above situation, the present inventors have
An approach that uses the image information value of the medium image, that is, the density value, which is changed non-linearly by the photosensitive characteristic (density characteristic curve) of the recording medium (photosensitive material) for producing a color print image. Instead of the first (raw, primitive) obtained from the subject (real image, real scene)
The method of producing a printed image based on the image information value related to the light amount such as the exposure amount was earnestly studied.

As a result, in the density gradation conversion operation which is primarily important in the color separation operation, (1) the density characteristic curve (photographic density characteristic curve) of the photographic light-sensitive material on which a color original image is photographed and recorded. The value of the horizontal axis (logE) is obtained from the density value of the vertical axis (D = logIo / I) (hereinafter, the vertical axis is also referred to as the D axis and the horizontal axis is also referred to as the x axis). In other words, the color original image ( The light amount value on the x-axis is calculated from the density value on the D-axis of the medium image), and (2) more specifically, the density information value on the D-axis of an arbitrary pixel point (n point) on the color original image ( D _n ) is projected on the X-axis through the density characteristic curve to obtain an image information value (x _n ) relating to the exposure amount of the corresponding pixel, and then (3)
Based on the x _n value (light quantity value) obtained as described above, and the gradation conversion formula proposed by the present inventors (this is the gradation conversion formula adopted in the present invention described later. However, the present invention is completely different in terms of usage and application of the gradation conversion formula.) When gradation conversion of an image is performed under the condition (substantial image) ,
It has been found that a color print image with excellent image quality that is faithful to real images is produced.

The gradation conversion technique previously proposed by the inventors of the present invention is, as is apparent from the above, the first meaning in producing a color print image of halftone dots. It is applied for the gradation conversion, which is important in particular. That is, the gradation conversion technology proposed by the present inventors has a fidelity of 1: 1 for the density gradation of various original images including color original images, and the human vision It is used to produce color reproduction images with natural gradation. The gradation conversion technology described above is not limited to standard color original images, but also non-standard originals (overexposed or underexposed, high-key or low-key originals, color fog or fading). Even in this case, it is useful for reproducing the density gradation that is recognized to be possessed by the subject (substantial image). In addition, it was confirmed that the tone conversion technology described above can reproduce a rich tone of color (color tone) based on faithful reproduction of density gradation.

However, as described above, the gradation conversion technology previously proposed by the inventors of the present invention is as follows. Firstly, the gradation conversion is emphasized in the color separation work. Emphasizing realization of density gradation Hi-Fi conversion (conversion of gradation with a high fidelity of 1: 1 between a continuous gradation original image and a halftone dot reproduction image) It was confirmed that the gradation conversion technology can perform the gradation conversion with high fidelity and rationally, and that the tone can be reproduced richly along with the gradation conversion.

By the way, the market needs for the quality of the color print image are not limited to the need to reproduce the color print image having the tone (gradation and color tone) according to the color original image, and become more sophisticated, complicated and diversified. It is coming. For example, a specific part (person, ceramics,
Clothes, furniture, woodworking products, paintings, etc.) or specific parts (areas) should be emphasized and reproduced, or the overall color tone should be blue, dark green, light green, pink, sepia. There is a need to change to the desired one. To meet these needs, for example, conventional color correction (color correction)
In the case of using technology, even if the color tone of a specific portion can be reproduced as required, the tone of the entire image is distorted and the image quality is severely deteriorated. Needless to say, in order to meet the above needs, we have established a gradation and color tone conversion technology that gives the human eye a natural feeling in both the tone of a specific portion or region (region) and the tone of the entire image. It is important to.

In order to meet the above-mentioned sophistication and complexity of market needs, it means that in the color separation technology, the gradation conversion technology and the color tone adjustment technology must be unified (integrated). It is a thing. In that case, for example, in the case of a color print image, the halftone dots forming the color print image always have gradation (tone) and color tone (color tone) or both density and color. It has a direct relationship with. This is natural because the image quality is determined by the size of the halftone dot (defines the density gradation) and the colored ink applied on the halftone dot (defines the color tone). . And
The present inventors have established means for rationally adjusting and managing the size of halftone dots (halftone dot% value) in the previously proposed gradation conversion technique. Therefore, the inventors of the present invention are keenly aware that the integration of the gradation adjustment technology and the color adjustment technology described above is an extension of the gradation conversion technology previously proposed by the inventors. Considered.

As a result, the inventors of the present invention have adopted the tone conversion formula, which is the core of the previously proposed tone conversion technique, and combined this with the idea of color tone adjustment. We have found that both gradations can be adjusted and managed rationally. The present invention was completed on the basis of the above-mentioned knowledge and bearing in mind the technical similarity found between a color scanner and an image forming apparatus for producing a color printed image. Color separation technology that rationally adjusts and manages both tones, and in particular, color tone management and adjustment technology that can adjust the tone to the desired one with rich tone reproducibility, which was difficult to achieve with conventional technology. An image forming apparatus incorporating the above is provided. The image forming apparatus of the present invention has a great feature in that it is equipped with the color separation technology in which both the gradation and the color tone are integrated as described above. However, in the following description of the present invention, in view of the current situation that the prior art cannot reasonably and quantitatively manage the color tone, in particular, the color tone of the gradation conversion unit, which is a core component of the image forming apparatus, It will be explained with emphasis on the management adjustment function.

[0025]

The present invention will be summarized as follows.
The present invention relates to an image forming apparatus for producing a halftone (halftone) color duplicate image by performing gradation conversion on image information of a continuous gradation color original image by a gradation conversion unit of the image forming apparatus. (1) Characteristic curve of recording medium on which color original image is recorded [Relationship between light quantity value (x value) incident on recording medium and density value (D value) formed on recording medium] The characteristic curve that defines the Dx orthogonal coordinate system] is used to obtain the light intensity value (x value) from the density value (D value), (2) The light intensity value (x value) is Tone conversion formula> is used to perform gradation conversion to obtain a gradation intensity value (y _n value),
And (3) a color tone adjusting function used during the gradation conversion, wherein the color tone adjusting function is (3) -1. H part (lightest part) to S part (darkest part) of the color original image. In the predetermined area between
A color tone management point (M ₁ ) for managing the color tone of the color reproduction image is set, and (3) -2. At the color tone management point (M ₁ ), the color tone adjustment condition is a desired color plate (C plate). , M plate, Y plate, and BL plate), and (3) -3. Level of the color plate that reflects the light amount value at the color tone management point (M ₁ ) and the adjustment condition of the color tone. The tone intensity value and the desired tone intensity values to be set in the H and S portions are substituted into the following <tone conversion formula> to determine the γ value, and the H of the color plate is determined.
A <grayscale conversion formula> for performing a grayscale conversion of the light amount values of the pixels from section S to section S into a grayscale intensity value (y _n value), and
(3) -4. <Gradation conversion formula> for each color plate whose γ value is determined
And an image forming apparatus having a color tone adjusting function configured to perform the gradation conversion of the light amount value of each pixel for each color plate and to manage and adjust the color tone. Is. <Gradation conversion formula> y _n = y _H + [α (1-10 ^−kx ) (y _S −y _H ) / (α−β)] In the above <Gradation conversion formula>, the meaning of each symbol is as follows. is as follows; x: shows the (x _n -x _H). That is, the color similarly obtained from the light amount value (x _n ) corresponding to the density information value (D _n ) at any pixel point (n point) of the color original image obtained by using the characteristic curve of the recording medium. The basic light amount value obtained by subtracting the light amount value (x _H ) corresponding to the density information value (D _H ) of the H portion of the original image is shown. y _n : Gradation intensity value set for a pixel on the color reproduction image corresponding to an arbitrary pixel point (n point) on the color original image. y _H : Gradation intensity value preset in the H portion on the color reproduction image corresponding to the H portion on the color original image. y _S : A gradation intensity value preset in the S portion of the color reproduction image corresponding to the S portion of the color original image. α: Surface reflectance of an image representation medium for recording a color reproduction image. β: Numerical value determined by β = 10 ^−γ . k: Numerical value determined by k = γ / (x _S −x _H ). However, x _S represents a light amount value (x _S ) corresponding to the density information value (D _S ) of the S portion of the color original image obtained by using the characteristic curve of the recording medium. γ: arbitrary coefficient.

The technical configuration of the image forming apparatus of the present invention will be described in detail below. For convenience of description, the image information value and the document image will be described here. In the image forming apparatus of the present invention, as image information used for producing a color print image from a color reproduction image, an image information value correlated with the density is used instead of using the image information value correlated with the density as in the prior art. There is a major feature in using information. Further, in the present invention, the color original image is one recorded or accumulated in a predetermined recording medium, and is also called a medium image. On the other hand, an image before being recorded or accumulated in the recording medium, that is, an object that is a true target of duplication is called a substantial image (subject, actual object, real scene). The color tone management method applied to the image forming apparatus of the present invention will be described below with reference to a color print image.

First, in order to gain an understanding of the present invention, a method of adjusting a color tone will be described in detail later. An outline of a gradation conversion technique using the <gradation conversion formula> will be described below.
explain. As described above, at present, a color scanner color separation device is very commonly used in the duplication work of a color print image, and the color separation work by the device is performed by a color original image (a transparent original and a reflection original as medium images). including.)
It is carried out based on the concentration information value obtained from.
More specifically, as a conventional method for producing a color print image, generally, a C plate (cyan) and an M plate (magenta) based on density information values obtained from a color original image (medium image) through R, G, and B filters. ), Y version (yellow), and BL version (black). However, for example, when a color film (transmissive type) original image (medium image) recorded on a recording medium called a photographic photosensitive material is used as a color original image, a method of utilizing the density information value taken from the image is It has the above-mentioned limitations (defects).

On the other hand, according to the present invention, as described above,
The true target of the copy is not the image recorded on the recording medium (medium image) but the literal color original image of the medium image, that is, the subject (substantial image) itself, and the image to be used at the time of duplication. The information value is based on the idea that the information value should be based on the image information value correlated with the amount of light incident on the recording medium from the subject. The above points are the basic differences between the gradation conversion technique of the present invention and the conventional technique.

This will be described below from another angle. In the color separation technique, it is necessary to convert a continuous tone color original image (for example, a transmissive color film original document) into a halftone dot color original image. A color separation curve (gradation conversion curve) defines the correlation between halftone dot images. The conventional color separation curve is formed on the D axis (density axis) of the photosensitive characteristic curve (photographic density characteristic curve defined by the D axis-x axis orthogonal coordinate system) of the photographic light-sensitive material as the recording medium. It is set based on the density information value. On the other hand, the color separation curve of the present invention is set on the basis of the image information value correlated with the light quantity of the subject (real image) on the x-axis of the photographic density characteristic curve as described above. That is, while the conventional color separation technology uses the D-axis color separation curve,
It can be said that the present invention uses the X-axis color separation curve, and both are basically different.

Next, a method of obtaining the image information value of each pixel of the color original image, that is, the light amount value in the image gradation conversion method using the <gradation conversion formula> of the present invention will be described.
First, from a characteristic curve of a photographic light-sensitive material as a recording medium used for photographing a color film original image (medium image), specifically, a photographic density value (D = logIo / I) and a subject (substantial image, real scene). A density characteristic curve showing the relationship between the image information value correlated with the amount of light incident on the photographic light-sensitive material as the recording medium, that is, the logarithmic value of the exposure amount (E = It) is prepared. Next, an arbitrary pixel (n
To determine light intensity values density value from (D _n) via the characteristic curves of the point) the (x _n), it is a function of the characteristic curves. For this purpose, for example, a density characteristic curve corresponding to the recording medium provided as a technical material by a photographic light-sensitive material manufacturer may be made into a function. If it can be reasonably functionalized, D
The D _n value on the axis can be easily converted to the x _n value on the x axis. Figure 1 shows the concentration characteristic curve (F company, Fujichrome)
Is shown. Further, Table 1 shows the result of formulating the concentration characteristic curve of FIG. In addition, as shown in Table 1, in order to formulate the concentration characteristic curve as accurately as possible, the formulating section is set to 8 sections, and the formulating is attempted in each section. It goes without saying that the more functional divisions, the more accurate the functional formula can be obtained.

[0031]

[Table 1]

In the mathematical expression of the density characteristic curve, an image information value correlated with the scale of the D axis indicating the density value of the color original image (medium image) and the light amount indicated by logE of the subject (substantial image). Assuming that the scales on the X-axis indicating the are the same, a function that defines the correlation between D and x was obtained. This is a kind of imitation made from the following viewpoints, and the present inventors consider that it is rational.
In this sense, the term canonical value is used on the X axis of FIG. That is, originally, in the photographic density characteristic curve, the logarithmic value of the exposure amount E on the X axis logE = logI ×
t) is located, which corresponds to the fact that the discriminative property for light and darkness of the visual sense is logarithmic as well as the perception of the density (visual sense) of the D axis, and thus the imitation on the above scale is reasonable. I think that is. It is needless to say that the above-mentioned grading in the present invention is a kind of simple method and is not limited to this.

In the present invention, the density value (D) of the color original image (medium image) formed by photographing and recording the subject (substantial image) on the recording medium (photosensitive material) as described above.
_n value) rather than based on, is to subject (entity image) correlated image information value to the amount represented by the x-axis is incident on the recording medium from the (x _n values) based. As described above, since the density characteristic curve is shown in Table 1 and the D _n value and the x _n value are correlated by the functional expression of x = f (D), it is easy to change the x _n value from the D _n value. You can ask.

Next, in the gradation conversion technique of the present invention, a color separation curve (gradation conversion curve) is obtained by using the light quantity value (x _n value) obtained as described above and the <gradation conversion formula>. That is, it suffices to obtain an x-axis color separation curve that replaces the conventional D-axis color separation curve and perform tone conversion of the image. That is,
For fabrication of a color print image, the image information values correlated to the amount of the corresponding pixel from under predetermined density characteristic curve, the concentration value at an arbitrary pixel (n point) on the original image (D _n) (x _The gradation intensity value (y _n ), that is, the halftone dot area% value (y _n ) is calculated by obtaining _n ) and substituting the (x _n ) value into the <gradation conversion formula>. Then, the gradation intensity value (y _n ) (halftone dot (area)% value) may be input to the output unit (halftone dot generator, dot generator) of the color scanner to produce a color print image.

The above-described <gradation conversion formula> derivation process of the present invention will be briefly described here. Halftone dot% value (y _n ) used when producing a color print image having the above-mentioned halftone dot gradation
<Gradation conversion formula> is a generally accepted density formula (photographic density, optical density), that is, D = logIo / I = log1 / T Io = incident light amount I = reflected light amount or transmitted light amount T = I / Io = It is derived from the reflectance or the amount of transmitted light. The general formula for the density D described above is applied to plate making / printing as follows. Density (D ') in plate making / printing = log (Io /
I) = log unit area × paper reflectance / [(unit area−
Halftone dot area × paper reflectance) + halftone dot area × ink surface reflectance] = log αA / [α {A- (d1 + d2 + ...
dn)} + β (d1 + d2 + ... dn)] where: A: unit area dn: area of each halftone dot within the unit area α: reflectance of printing paper β: surface reflectance of printing ink.

The present invention is based on the density formula (D ') relating to plate making and printing, and a basic density value (x) at an arbitrary sample point (pixel) (n point) on a continuous tone color original image, In order to associate the theoretical value with the actually measured value in association with the halftone dot% value (y _n ) of the halftone dot at the sample points on the color print image corresponding to this halftone gradation, Is derived.

In the operation of the <gradation conversion formula> of the present invention, generally 5% for y _H , 95% for y _S for C plate, 3% for y _H and 90% for y _S for M plate and Y plate. Is used. In the operation of the <gradation conversion formula>, if the densitometer measurement value is used for the density value and the percentage value (% value) as described above is used for y _H and y _S , the y _n value also becomes the percentage value ( % Value).

In the operation of the <gradation conversion formula> of the present invention, it is possible to use it by modifying it as follows as well as using it by arbitrarily processing, deforming or guiding it. y _n = y _H + E (1-10 ^−kx ) · (y _S −y _H ), where E = 1 / (1−β) = 1 / (1−10 ^−γ ), α = It is one. This is one in which the surface reflectance of the printing paper (base material) used for expressing a color printing image is 100%. The value of α may be any value, but may be 1.0 in practice. This also applies to intensity images such as video images.

Further, according to the modification (alpha = 1.0), a y _H in the brightest part (H portion) of the color print image, as was expected a y _S to darkest part (S unit) It can be set, which is a great feature of the present invention. By the definition, the above-mentioned point is that x = 0 in the H part on the color print image, and x = x _S in the S part.
It is the -x _H, i.e., -k · x = γ · ( x S -x H) / (x S -x H) = - is evident from the fact that the gamma. Thus, the present invention <
By using the gradation conversion formula> (a modified example of a = 1), it is possible to always set the planned y _H value and y _S value in the H portion and the S portion on the color print image. This point
This is a very important point for users to evaluate and consider the work results. That is, y _H and y _S in the color print image
Set the desired value to and change the γ value (however,
= 1.0), various x-axis color separation curves (gradation conversion curves) can be obtained. Then, the image quality content of the color print image produced under these x-axis color separation curves can be easily evaluated in relation to the γ value.

X of each color plate for multicolor plate making (generally, four plates of C plate / M plate / Y plate / BL plate are used) utilizing the <gradation conversion formula> of the present invention. To set the axis color separation curve (gradation conversion curve), the following may be done.
In the industry, it is common practice to first set a reference C color separation curve (gradation conversion curve), and then set the other color plates so that the gray balance and color balance are maintained. Is. The maintenance of the gray balance described above is a condition for reproducing a neutral density (gray) by three color plates (C / M / Y plates) and is a main requirement. In the industry, standard values shown in Table 2 below are generally adopted in order to maintain the gray balance. In Table 2, M ₁ is a gray balance management point (hereinafter, also referred to as an intermediate point) set in the intermediate portion of the dynamic range (density area) of the H portion to the S portion. In the industry, the M ₁ point is generally set at a dot% value of C plate of 50% as shown in Table 2.
The main reason that the M ₁ point is set to the halftone dot 50% value of the C plate is that it is widely recognized that the halftone dot% value region is a reproduction region with rich gradation. From Table 2, in the art, in the M ₁ point (halftone), the halftone dot value of C plate is 50%, and the halftone dot value of other color plates (M / Y plate) is 4%.
It is understood that the gray balance is maintained by setting it to 0%.

[0041]

[Table 2]

As described above, the gradation conversion technique of the present invention is
In producing a color print image, the density information value (D _n ) obtained from a color original image (medium image) is not used, but is incident on a recording medium for forming a medium image from a subject (substantial image). It is premised that the image information value (x _n ) correlated with the amount of light is used and the <gradation conversion formula> is used, and the color has gradation characteristics faithful to the subject (real image). It is possible to produce a print image, and further, a color print image in which gradation characteristics are changed to a desired one, with work regularity, universality and elasticity.

Next, the core technical constitution of the present invention, that is, incorporating the tone adjustment technique into the above-mentioned tone conversion technique, in other words, integrating the tone conversion technique and the tone management adjustment technique Will be described. The trigger for the integration of the gradation and the color tone was as follows. (1) The <gradation conversion formula> proposed by the present inventors and used also in the present invention is the halftone dot of all the pixels from the H portion to the S portion of the color print image as described above. (Dot)
The halftone dot% value (in other words, the size of the halftone dot) of the original faithfully reproduces the gradation characteristic of the color original image, and the gradation characteristic is natural to human vision. It is an important tool for adjusting to. (2) The halftone dot value set for each pixel always has a direct relationship and influence on both gradation and color tone (or density and color). (3) As market needs, not only 1: 1 reproduction of color original image (Hi-Fi reproduction), but also enhancement of color tone of specific part of image, specific part of dynamic range of H part to S part,
The number of cases requiring (changing) changes and modifications is increasing. In addition, in the above request, customers and designers
The request contents are presented and specified by halftone dot% values by a color chart owned by them (which will be described later in detail). (4) In the case where the above needs are met by the conventional color separation technology, particularly the conventional color correction (color correction), even if the color tone of a specific portion is approximated to the requested content,
In many cases, the tone (gradation and color tone) of the entire image is distorted, and the value of the product is lost.

The color chart is a basic scale (reference table) for color reproduction in which all the colors are expressed by halftone dot density gradations using the printing process 4 primary color inks. For example, "DIC GRAF-G Color Chart" issued by Dainippon Ink and Chemicals, Inc.
(March 1991). In the color chart, there are various combinations as shown below as combinations of each color plate for color reproduction. 1. Basic combination: C (cyan) and M (magenta)
There is a chart based on the combination of. For example, (C) is printed on the vertical axis and (M) is printed on the horizontal axis in 12 gradations with halftone dot% values of 0 to 100% to form a basic pattern. There is a structure in which Y (yellow) and BL (sumi) having a% value are printed and overlapped. As Y or BL of the constant halftone dot% value, Y = 10
%, BL = 10%, Y = 10%, BL = 30
%, Y = 50%, BL = 10%,
and so on. 2. Other combinations: (1) A combination of (Y) on the vertical axis and (M) on the horizontal axis,
(2) A combination of (C) on the vertical axis and (Y) on the horizontal axis,
(3) Combination of (BL) on the vertical axis and (Y) on the horizontal axis,
(4) Combination of (BL) on the vertical axis and (M) on the horizontal axis,
(5) Combination of (C) on the vertical axis and (BL) on the horizontal axis.

As described above, the color tone on the color chart is specified by the halftone dot% value of each color plate (C / M / Y / BL). Therefore, in response to a color tone change request from a customer or a graphic designer based on the color chart, a technology for quantitatively and rationally managing and adjusting all halftone dot% values of each pixel is used as a color separation technology. It goes without saying that we must secure it.

From the background described above, the present inventors have
The gradation conversion formula> has the ability to completely quantitatively and reasonably manage and adjust the halftone dot value of all pixels from the H point to the S point, and is therefore effective for adjusting the color tone. I thought it would be a powerful tool. This is an opportunity to develop a color separation technique that integrates gradation and color tone using the <gradation conversion formula> as a main tool.

As described above, the image forming apparatus of the present invention incorporates the color separation technology in which the gradation adjustment and the color adjustment are integrated into the gradation conversion unit which is the core component thereof. It has characteristics. In particular, in the present invention, the color separation technique incorporating the color tone management adjustment is significantly different from the conventional technique, and this point will be described below.

1. First, a color tone management point (M ₁ ) for managing the color tone of the color reproduction image is set at a desired portion between the H portion and the S portion of the color original. In the present invention, the same symbol (M ₁ ) as the halftone point (M ₁ ) for maintaining the gray balance in Table 2 is used as the symbol of the color tone management point (M ₁ ). This reflects that the tone reproduction in the halftone region is an important point in the color separation technique, and thus is also important in the tone reproduction. Needless to say, the color tone management point (M ₁ ) is not limited to the halftone point for maintaining the gray balance, and may be a desired point between the H portion and the S portion. .
The color tone management point (M ₁ ) displays a vertical axis (y-axis: halftone dot% value) and a horizontal axis (x-axis: light amount value), as will be described later in the embodiment and in FIG. .) Cartesian coordinates are displayed with the light amount value on the horizontal axis. Since the light quantity value correlates with the density value of the color original image, it may be displayed as the density value.

2. Next, at the color tone management point (M ₁ ) designated as described above, the color tone adjustment condition is determined by the halftone dot value of the desired color plate (C plate, M plate, Y plate, and BL plate). To do. The specific content of the adjustment (change) condition of the color tone is as described in the description of the color chart.

3. The next step is to use each of the color plates (C plate, M plate, Y plate, BL
Preparation of the color separation curve (gradation conversion curve) used for producing the color separation image of (version), more specifically, the <gradation conversion formula> for setting the color separation curve for each color plate. Preparation. By the above steps (1 to 2), the light quantity value of the color tone management point (M ₁ ), for example, M ₁
= 0.400, ・ Color tone adjustment conditions, for example, C plate halftone dot% value (50%),
Halftone dot value for M plate (20%), Halftone dot value for Y plate (10%), B
L halftone dot% value (10%) is set. The halftone dot% values (y _H , y _S ) set in the H and S parts of each color plate are set to values given in advance or desired values. It should be noted that the y _H value and the y _S value given as the above-mentioned conditions are C,
It means 5% and 95% for the plates, respectively, and 3% and 90% for the plates M and Y, respectively (see Table 2). Under the above conditions, the γ value of the <gradation conversion formula> used to determine the color separation curve for each color plate is determined. For example, the γ value of the <gradation conversion formula> for determining the color separation curve for C plate is determined as follows. In the above <gradation conversion formula>, x _H = 0.00, x _S = 1.00, x _n = M ₁ = 0.4
0, α = 1.00, y _H = 0 (%), y _S = 95
By substituting (%), y _n = 50% for solving, a value of γ = 0.45 is obtained. As a result, <gradation conversion formula> for setting the color separation curve for C plate is prepared. The same applies to other color plates.

4. The next step is the γ value (0.
45) is used, the light amount values (x _n ) of all pixel points (n points) from the H section to the SH section are subjected to gradation conversion, and the C separation color separation curve ( This is a step of obtaining a gradation conversion curve). In other words, the color separation work is performed using the <gradation conversion formula> for the C plate in order to produce the C plate color plate image. The same applies to other color plates.

With respect to the image forming apparatus of the present invention, particularly the characteristics of the gradation converting section which is the central mechanism (main component), the gradation converting section of the color scanner for producing a color print image is taken as an example. Explained. However,
The image forming apparatus of the present invention is not limited to a color scanner for producing a color print image for the following reasons. As is well known, various methods are known as a method of expressing a halftone (halftone) gradation pixel. For example, a method of changing the pixel coverage by the size of a dot (also called a size modulation method. This method is found in monochrome and color scanners for producing printed images, piezoelectric ink jets, etc.) or a regulation. A method of changing the pixel coverage by the number of dots of the same size (also called a density modulation method. This method is found in thermal fusion transfer). A method of changing the density (also called a direct density modulation method. This method is found in thermal sublimation transfer. In addition, a TRT composed of a CRT or liquid crystal that forms a pixel by adjusting the brightness of the pixel.
V receivers are also included in this category. ).

The above-described various pixel expression methods are all rationally operated by the gradation conversion method described above. That is, the image forming apparatus of the present invention includes devices that adopt the above-described various pixel expression methods. In other words, the image forming apparatus of the present invention should be construed in the broadest sense, and includes a copying machine, a printer machine, a plate making machine,
This applies to all those having a function of producing a color duplicate image, such as image transmission equipment, TV image pickup equipment, and electronic camera equipment.

In each of the various image forming apparatuses, the y _n value (gradation intensity value) obtained by the calculation processing of <gradation conversion equation> is used as a gradation display method (variable dot method, variable dot method, etc.) suitable for each image forming apparatus. It goes without saying that the constant dot system, the variable density dot) or the brightness display system may be used. For example, as shown in FIG. 2, in the case of the column of FIG. 2A, the distribution of the pixels recorded in a predetermined pixel block is such that the distribution of positions in the pixel block is mutually dispersed as the number of recorded pixels increases. Although there is a relationship, it is possible to make the spiral block outwardly expand from the center portion of the pixel block, for example, and in that case, it approximates to a halftone dot in photoengraving. In the column of FIG. 2B, halftone dots having an area corresponding to the number of pixels in the column of FIG. 2A are shown. Although the pixel block has been described as a 4 × 4 matrix type here, 17 gradations are expressed by this. Generally, in an n × n matrix-type pixel block, n ² +1 gradations (0 to 0)
100%) is expressed. Such a method of expressing the gradation of a continuous gradation original image by the distribution of pixels formed in the matrix type pixel block is generally called a dither matrix method and is well known (for example, Japanese Laid-Open Patent Publication 58-85434, 58-114569,
59-53969, 60-141585, 6
2-186663 and the like).

The image forming apparatus of the present invention has the greatest characteristic point in the color separation technique incorporating the gradation conversion and color tone adjustment functions in the gradation conversion unit. This will be described below. The image forming apparatus of the present invention uses various color original images, that is, various color original images obtained by recording, photographing, or image-converting a subject (substantial image) on a desired recording medium by using information transmission media such as light and electromagnetic waves. (Medium image) can be used. Examples of the recording medium for the color original image include a transmission type color film (photosensitive emulsion), a photoelectric conversion element such as a two-dimensional CCD or a photodiode, an optical disk or a porcelain disk. It goes without saying that a reflection original such as a painting or a color print can be used as the color original image.

In order to obtain the light quantity value from the density information value in the various recording media described above, a photographic density characteristic curve or a photoelectric conversion characteristic curve may be used depending on the type of the recording medium. It should be noted that reflective documents such as paintings and color prints are treated as if their characteristic curves correspond linearly with a density information value and a light intensity value of 1: 1 (corresponding to a linear relationship of 45 °). Needless to say, that is all right.

In the image forming apparatus of the present invention, if a density characteristic curve (photoelectric conversion characteristic curve) peculiar to these recording media can be defined as a recording medium such as a photodiode or CCD constituting the above-mentioned recording medium system. The performance of the recording medium is sufficient, and it is possible to produce a color reproduction image having excellent gradation (density gradation and color tone) by using these recording media. That is, attempts are being made to improve the characteristics (photosensitive characteristics and photoelectric conversion characteristics) of various recording media in an attempt to produce high-quality color reproduction images (for example, high dynamic range and linearity of characteristic curves). In order to produce a color reproduction image according to the present invention, it is not always required that various recording media have high quality and high performance, and existing performances (characteristics) are sufficient. This is due to the gradation conversion technology incorporated in the image forming apparatus of the present invention, and constitutes another feature of the present invention.

Next, in the image forming apparatus of the present invention, the structure of the gradation conversion unit, which is the main constituent element (mechanism) of the above-mentioned gradation and color tone adjustment, will be explained to perform color separation. 1. In the present invention, the gradation conversion unit is configured as follows, for example. (1) A density information value obtained from a color original image recorded on a predetermined recording medium (sensor), and an image information value correlated with the amount of light incident on the recording medium (sensor) from a subject (actual image) The image information value and / or the image information electric signal value (either analog or digital) relating to the density of a color original image (including a hard original and a soft original) based on a density characteristic curve that defines the correlation between It is also possible to provide a mechanism (for software) that obtains an image information value correlated with the light amount corresponding to (2), and (2) a mechanism (for software) that operates the <tone conversion formula>. .

2. Further, the configuration of the output unit is such that the current value and voltage value of the recording unit (recording head) of the device are associated with the calculated value by the <gradation conversion formula>, that is, the y _n value (gradation intensity value).
Alternatively, by controlling the application time, etc., the size of dots and the array density of dots are changed (the size modulation method or the density modulation method is adopted), and the half tone (halftone dot level) in which the gradation and color tone are adjusted as desired. It is sufficient to configure so that a color duplicate image of (tone) is output. The y _n value of the present invention is also called a halftone dot value in connection with the technique of a color printing image reproduction technique, but is generally called a gradation intensity value as described above. The y _n value of the present invention should be construed in the broadest sense regardless of its nominal law.

For example, a small spot light is applied to a color film original image (transmissive medium image), and the transmitted light (image information signal) is converted into a photoelectric conversion unit (photomul or CC).
D) receives the light, converts the intensity of light into the intensity of voltage, digitizes the obtained image information electrical signal (voltage value), and performs necessary organization and processing by a computer, that is, by <gradation conversion formula> A gradation reproduction is performed, and the output section of the image forming apparatus is operated based on the gradation intensity value (y _n value) output from the computer, and ink is ejected onto the recording paper in synchronization with the input system to produce a color reproduction image. It is sufficient to use a well-known existing system for creating.

At this time, the computer processing mechanism for organizing and processing the image information electric signals of the color original image (medium image) is reconfigured, and the color original image (recording medium) recorded on the color film (recording medium) is reconfigured. The image information value correlated with the light amount is obtained from the density information value of the medium image) through the density characteristic curve of the color film (recording medium), and the halftone dot value (y _n value)
All you have to do is to incorporate software that outputs.

As can be seen from the above description, a color original image (a medium image photographed and recorded on a recording medium called a photographic photosensitive material) is an image information acquisition mechanism (detection unit) of the image forming apparatus, specifically, photoelectric conversion. The image information value correlated with the density is obtained by being processed by a unit (photomul or CCD). Strictly speaking, since the photoelectric conversion unit has its own characteristic curve (photoelectric conversion characteristic curve), in the photoelectric conversion unit, the image information of the color original image is equivalent to that of the photoelectric conversion unit. It will be affected (altered or deteriorated) by the photoelectric conversion characteristic curve. Therefore, it is preferable to eliminate the influence of the photoelectric conversion characteristic curve, but this may be ignored. In other words, the image information of the color original image is
Influenced by the photoelectric conversion characteristic curve of the photoelectric conversion unit (alteration,
Deterioration). Therefore, it is preferable to eliminate the influence of the photoelectric conversion characteristic curve, but this may be ignored in consideration of the characteristics of the photoelectric conversion unit.

As the software applied to the above-mentioned gradation converting unit, image information which correlates the density information value (D _n ) correlating with the density of the color original image with the corresponding light quantity under a predetermined density characteristic curve is used. A general-purpose computer that converts into a value ( _xn ) and has the algorithm of <gradation conversion formula> as software and has an A / D (analog-digital conversion) and a D / A I / F (interface), An electrical circuit that embodies a general-purpose IC with the algorithm as logic, and an RO that holds the algorithm operation result
Various forms such as an electric circuit including M, a PAL in which an algorithm is embodied as an internal logic, a gate array, a custom IC, and the like can be taken. Particularly in recent years, modularization has been developed, and an arithmetic mechanism capable of performing gradation conversion of an image based on the above <gradation conversion formula> of the present invention is a dedicated IC, LSI, microprocessor, or microprocessor. It can be easily manufactured as a module such as a computer.

Next, the related matters for exhibiting the color tone adjusting function in the gradation converting section of the image forming apparatus of the present invention will be specifically described. In the case of an image forming apparatus, each color plate (C / C
(M / Y / BL) is not manufactured individually and is not overprinted, but each color is continuously superimposed under sequence control. However, for convenience of description, in the following description, it is called a color plate image that statically captures each color image, and in relation to this, a C plate image (color plate image), a C plate separation curve (gradation conversion curve), etc. Is used.

(1) Determination of Color Tone Management Point (M ₁ ) The color tone management point (M ₁ ) may be any point between the H section and the S section. However,
In order to reproduce rich gradation in a monochrome print image or a color print image, a halftone, more specifically, a point where the halftone dot value of the C plate image (color plate image) is 50% is widely adopted as a management point. ing. Therefore, also in the image forming apparatus of the present invention, as the management point (M ₁ ) of the color tone, the region of the gradation intensity value (y _n value) = 50% in the C plate color separation curve (gradation conversion curve) is selected. Is preferred. The above-mentioned color tone management point (M ₁ ) is coded as a standard condition (see Table 2) for maintaining the gray balance at the time of producing a color print image. In the present invention, as described above, the color tone management point (M ₁ ) is
It goes without saying that the gradation intensity value (y _n value) is not limited to 50%.

(2) Light intensity value (x value) of color tone management point (M ₁ ) The light intensity value (x value) of color tone management point (M ₁ ) may be determined as follows. In each color plate of the image forming apparatus, it is preferable to set a reference color separation curve (gradation conversion curve) and set the other color plates so that gray balance and color balance are maintained in relation to this. This idea is the same as the production of a color print image. Therefore, as in the color printing technique, the reference color plate is the C plate, and (i) the desired γ value, for example, γ = 0.45 used when the color print image is produced, and (ii) the desired y _H , Y _S , α
Value, for example, y _H = 0%, y used when the printed image was produced
_S = 95%, α = 1.00. <Gradation conversion formula> is operated under the condition of (1) to set the color separation curve for C plate (gradation conversion curve). Next, in the color separation curve for C plate (gradation conversion curve) determined as described above, y _n = 50%
The light quantity value (x value) that satisfies That is, the above condition may be substituted into <gradation conversion formula> to solve the following formula. In this case, a light quantity value of x = 0.40 is obtained. 50 = 0 + [(1-10 ^-0.45x ) (95-0) / (1-
10 ^-0.45 )] (Note) In the operation of <Gradation conversion formula>, x _S −
x _H = 1.000. Generally, the dynamic range (x _S of the light amount value obtained from the color original image (medium image) is calculated.
Although −x _H ) is not 1.00, here, a value obtained by normalizing the dynamic range to 1.00 is used.
Needless to say, even if the dynamic range is normalized to 1.00, the image quality contents are changed relative to each other, so that there is no problem in image processing.

(3) Method of Determining γ Value for Determining Color Separation Curve for Each Color Plate (C / M / Y / BL) As described above, the color separation curve for C plate (gradation conversion curve)
The γ value for setting is determined as γ = 0.45. For other color plates, the γ value for setting the color separation curve must be obtained according to the content of the color tone adjustment conditions. For example, in the case of the M plate, at the color tone management point (M ₁ ) (this x value is x = 0.40), the gradation intensity value (y _n value) of the M plate is 20%, and under the initial conditions. The gradation intensity value (0%) of a certain y _H portion and the gradation intensity value (68%) of a y _S portion are substituted into the <gradation conversion formula> to obtain the γ value for the M plate. That is, γ = 0.20 is obtained from the following formula. 20 = 0 + [(1-10- ^{γ (0.40)} ) (68-0) /
(1-10 ^−γ )] In the image forming apparatus of the present invention, the light intensity value at the color tone management point (M ₁ ) and the γ value for each color plate are automatically calculated, and a desired color separation curve is prepared. The above software may be installed in the gradation conversion unit.

[0068]

The image forming apparatus of the present invention will be described in more detail with reference to the drawings. FIG. 3 is a block diagram of the image forming apparatus according to the first embodiment of the present invention. As shown in FIG. 3, in the image forming apparatus of the present invention, the transmitted light or the reflected light of the color original image is converted into R (red), G (green), and B (green).
A detection unit (1) for spectrally reading (blue) and output signals of the detection unit (1) are C (cyan), M (magenta), and Y.
(Yellow), K (Black) (hereinafter BL as a symbol
Use K instead of. ), A color separation unit (2) for converting the color separation signal into a color separation signal, and a gradation adjustment for processing the color separation signal using the <gradation conversion formula> of the present invention so that an appropriate gradation image is produced. It is formed on the photoreceptor by four blocks, namely, a section (3) and an output section (4) which exposes the electrophotographic photoreceptor with laser light based on the output signal of the gradation adjusting section (3). The latent image is developed in the developing unit to form a toner image, which is transferred to the recording sheet and fixed in the fixing unit. In order to form a color image, an independent photoconductor and a developing unit are provided for each component color so that the toner images formed are transferred sequentially to a recording sheet, or the latent image of the component color is formed on one photoconductor. An image is formed and developed into a toner image, then transferred to a recording sheet, and this process is repeated for each color component.

In the present invention, among the four blocks,
The detection unit (1), the color separation unit (2), and the output unit (4)
The mechanism and configuration generally adopted in the conventional image forming apparatus are used as they are. In other words, the gradation adjusting unit (3) is the object of the improvement of the present invention. Strictly speaking, the gradation conversion unit based on the <gradation conversion formula> which integrates the gradation and color tone adjustment of the present invention to perform color separation is a color separation unit. It is also related to the function improvement of (2). Therefore, the image forming apparatus of the present invention is configured by using the color separation unit (2) of the existing image forming apparatus and changing the configuration of the conventional gradation converting unit to the gradation converting unit of the present invention. It can be said that

The structure of the image forming apparatus of the present invention will be specifically described below. The detection unit (1) detects the transmitted light or the reflected light of each part of the color original image (5) by a photoelectric conversion element such as a photomultiplier, and detects R, G, B, and USM signals as current values. Is output, and this signal is converted into a voltage signal in the A / V converter (6). The color separation unit (2) logarithmically calculates the respective voltage signals of R, G, B, and USM of the detection unit (1) in the log amplifier (7) to convert the signals into concentrations, and basic masking (BM)
In (8), the C / M / Y color components (basic color components) are separated and the black (K) component is separated. That is, in the image forming apparatus of the present invention, a document image (5) which is an object to be reproduced (color print or color print).
First, the image information for each color (R, G, B) is first detected by the image information reading mechanism configured by a photomultiplier or a solid-state image sensor (CCD) in the detection unit (1) by a conventional method, and the color separation unit In (2), the density information value (D _n ) for obtaining the color reproduction image by color separation is obtained. This is obtained for each color (C, M, Y) component (basic color component) as described above.

The density information value (D _n ) is a characteristic curve of the recording medium system, for example, a photoelectric conversion characteristic curve of the CCD which is the recording medium, and is used as an image information value (x _n ) correlated with the light amount.
Further, it goes without saying that it is converted into the basic light amount value (x). In addition, in order to obtain the image information correlated with the above-described light amount, it may be performed by software or hardware (not shown). In the present invention, the image information value (x _n ) correlated with the amount of light from the density information value (D _n ) described above.
The function of obtaining the basic light amount value (x) may be incorporated in the gradation adjusting unit (3) described below. This is because the gradation adjustment unit (3) operates an algorithm of <gradation conversion formula>, and the image information of the light quantity value correlation is also obtained by a predetermined algorithm, so that the calculation functions are integrated. It is based on the idea. Needless to say, the present invention is not limited to this method.

FIG. 3 shows a color correction (CC) section (9) as a structure of the color separation section (2). Here, for each original color of R, G, B and C, M, Y, C
Components, M component, and Y component are controlled, and the K component of the original is further controlled by the UCR (under co
lor removal) or UCA (uncer color additio)
In n), the ratio represented by three types of inks of C, M, and Y and the ratio represented by K (black ink) are determined.

In this way, the C, M, Y and K components converted into the image information value correlated with the light quantity are converted into the gradation conversion unit (1
In 1), conversion from C, M, Y, K into pixel density values (gradation intensity values) in pixel blocks of each color component, that is, ce ', me', ye ', ke' indicating the effective area ratio of each color component. I do. The gradation conversion unit (11) uses an characteristic curve of a recording medium on which a color original image is recorded, and obtains a light amount value (x _n ) value from a density value (D _n ) and a gradation conversion formula. > Has a calculation algorithm. And for each of C, M, Y, K
Gradation conversion formula> is applied, and ce ', me', ye ', ke
Ask for ´.

The gradation conversion unit (11) has an algorithm of <gradation conversion formula> as software and
/ D, D / A general-purpose computer having I / F (interface), general-purpose I using algorithm as logic
Various forms such as an electric circuit embodied by C, an electric circuit including a ROM holding the operation result of the algorithm, a PAL embodying the algorithm as an internal logic, a gate array, a custom IC, and the like can be taken.

The effective area ratio corresponding to the pixel density value of each color component obtained by the gradation conversion unit (11) is input to the color channel selector (CHS) (12) and the color channel selector (CHS) (12). Is ce ', me
′, Ye ′, and ke ′ are sequentially output at the time of selection. This output is A / D converted by the A / D converter (13) and input to the output unit 4. That is, each color is input to the dot control (D / C) unit (14). The dot control (D / C) section (14) controls the output value of the laser beam generator (15).

<Basic Experiment> Next, in the above-described image forming apparatus of the first embodiment of the present invention, the core gradation conversion unit (11) integrally adjusts the gradation and the color tone of the color reproduction image. I confirmed whether I had the ability to do it. In particular, a basic experiment was conducted in the following manner in order to confirm whether the color tone could be adjusted rationally while maintaining the gradation. Since this is a basic experiment, only the color plate (C / M / Y plate) was tested, and the BL (K) plate was not used. (1) Color original image A standard quality brown pottery jar (transparent original) was used as the color original image. (2) Design material for each color plate Table 3 shows the design material for each color plate for the management and adjustment of color tone as a basic experiment. (Note 1) In the experiment A, the tone intensity value (y _S ) of the S portion was designated first, and then the tone intensity value of the M ₁ point (color tone control point) was obtained by the following equation (1) and the experiment was conducted. It is a thing. In addition,
The standard values of the following formula (1) are shown in Table 2. Dot% values of M ₁ point = (standard value of M ₁ point) × (tone intensity value specified in the S portion) / (standard value of the S portion) ......... (1) (Note 2) Experiment B is , M ₁ was adopted as the gradation intensity value of Experiment _{1, and} the standard value (Table 2) was adopted as the gradation intensity value of the S portion. (Note 3) Since the catch light portion is selected as the H portion of the color original image (pot), the halftone dot% value of the H portion of all color plate images is "0".

[0077]

[Table 3]

The four experimental results of the basic experiment were all as expected in the light of experience. This means
The color tone management method using the <gradation conversion formula> of the present invention is rational. The contents of the four color reproduction images obtained from the basic experiment are as follows. (1) At all four points, the gradation (density gradation) is well reproduced in the entire dynamic range of the H to S parts, and the halftone volume feeling is also suitable for human vision. (2) The color tone of the vase is blue in Experiment A (No. 1 to No. 2), blue in the halftone area in Experiment B (No. 1 to No. 2), and the original image is in S part. It was a brownish street. It should be noted that these color tones are exactly the same as in practice.

Incidentally, the γ value for setting the color separation curve for each color plate of Experiment A (No. 1 to No. 2) and the halftone dot value (calculated value) at M ₁ point are as follows. (1) Experiment A (No. 1) C version γ = 0.45,% dot value of M ₁ point = 50.0000% M plate γ = −0.20,% dot value of M ₁ point = 30.9878% Y version γ = -0.18, M ₁ dot half value = 35.8678% (2) Experiment B (No. 2) C version γ = 0.45, M ₁ dot half value = 50.0000 % M version γ = -0.18, M ₁ point halftone dot% value = 26.9006% Y version γ = -0.20, M ₁ point halftone dot% value = 30.9878% Note that the BL version γ value is γ = -0.25.

The outline of the basic experiment and the experiment A (N
Fig. 4 shows the color separation curve (gradation conversion curve) for each color plate used in o. 1) and execution B (No. 1). (A) in the figure
Is a combination of color separation curves that has been adopted as a standard in the industry for maintaining gray balance. The design materials are given in Table 2. (A) in the figure is a combination of color separation curves (gradation conversion curves) of each color plate of Experiment A (No. 1), and (B) is Experiment B (No. 1).
The combination of color separation curves (gradation conversion curves) of each color plate is shown.

<Application Experiment> In this experiment, a color separation experiment is performed by a method closer to the daily color separation work, and the color tone management method using the <tone conversion formula> of the present invention determines the color tone of the color print image. The purpose is to check whether or not it has a function for reasonably adjusting and managing. In this experiment, the tone control value (M ₁ ) was set so that the tone intensity value of the C plate image was 50%.
It became the point that becomes. In addition, the details of the adjustment of the color tone at the color tone management point (M ₁ ) (specific details of the correction and change of the color tone requested by the user, etc.) are defined by the halftone dot% of each color of C / M / Y of each color plate image. "DIC GRA" manufactured by Dainippon Ink and Chemicals, Inc. is used as the basic scale specified by the value.
FG Color Chart "(March 1991, second edition)
It was adopted. In this experiment, the halftone dot value of the color chart was read as the gradation intensity value (%) and adopted. In this experiment, six colors were selected from the color chart. In Table 4, the above-mentioned "DIC GRAF-G
6 types of colors selected from the "color chart" and designated gradation intensity values for color tone adjustment are shown.

In the above-mentioned color chart, the above-mentioned 6 kinds of colors have a gradation intensity value of C / M of 12 between 0 and 100.
It is displayed in stages, and Y / BL (having a constant gradation intensity value, for example, a gradation intensity value of 10% or 50% as shown in Table 4) is shown as a color overprinted thereon. Has been done. Therefore, the specified gradation strength value for color tone adjustment can be easily specified in the same chart, and Table 4 shows the specified gradation strength value. Needless to say, it is possible to examine whether or not the color specified by the above gradation intensity value is faithfully reproduced on the color plate image without causing deterioration of gradation. , The purpose of this experiment.

[0083]

[Table 4]

Table 5 below shows each color plate design material for this experiment prepared based on the material of Table 4 above. (Note 1) In this experiment, it is needless to say that the gradation intensity value at M ₁ point is the specified gradation intensity value for color tone adjustment in Table 4. (Note 2) In the experiment A of this experiment, the gradation intensity value for the M / C plate of the S part was obtained by the following equation (2). For C plate, the value in Table 2 (standard value for maintaining gray balance) (95%)
It was adopted. The standard values of (2) below are shown in Table 2. When the calculation result by the following formula (2) exceeds the standard halftone dot% value, the standard halftone dot% value is adopted. S portion of the dot% value = (standard value of the S portion) × (tone intensity value specified in the M ₁₎ / (standard value of M ₁₎ ......... (2) (3) color original image (pot Since the catch light portion is selected as the H portion of), the halftone dot% value of the H portion of all color plate images is “0” (zero). (Note 4) The BL version (black) version is a skeleton type, that is, the starting point (SP) of black ink is M
_One point was set, and the end point (EP) was set as the S section. In addition, the maximum halftone dot% value of the BL plate put in the S part is 8 in Experiment A.
0% and 70% in Experiment B.

[0085]

[Table 5]

The results of the applied experiments were all as expected, as in the basic experiments. The color tone at the color tone management point (M ₁ ) obtained in the color reproduction image is completely in agreement with the color tone on the color chart as the basic scale, and the gradation is not limited to the entire dynamic range of the H part to the S part. The color tone was also natural to human eyes. That is, based on the results of the above-mentioned applied experiments, the color separation technique using the <tone conversion formula> of the present invention as a tool further integrates the tone adjustment and the tone adjustment when performing the tone adjustment management. Above, it was confirmed to have rationality.

FIG. 5 is a block diagram of an image forming apparatus according to the second embodiment of the present invention. The image forming apparatus of the second embodiment uses the conventional inverse log transformation unit (16) as it is,
Therefore, in the gradation conversion unit (11), ye is expressed in logarithmic form.
′, Me ′, ce ′, ke ′ are output. As a result, the <gradation conversion formula> can be applied only by converting one component in the conventional device, and the existing system can be applied to the image forming apparatus of the present invention with fewer changes than the first embodiment. Can be modified.

FIG. 6 shows an image forming apparatus according to the third embodiment of the present invention. In the image forming apparatus of the third embodiment, the conventional gradation control (IMC) unit (17) is left as it is, and the connection between the inverse log conversion unit (16) and this gradation control unit (17) is cut off. Then, as in the second embodiment, a gradation conversion unit (11) that outputs ye ', me', ce ', ke' in logarithmic form is adopted. The gradation conversion unit (11) starts from the previous stage of the gradation control unit (17) in Y, M,
The signals of C and K are taken and the converted value is output to the inverse log converter (16).

FIG. 7 shows an image forming apparatus according to the fourth embodiment of the present invention. In the image forming apparatus of the fourth embodiment, the inverse log converter (16) and the color channel selector (12) are left as they are, and the connection between them is cut off. That is, the gradation conversion unit (11) receives Y, M, C, and K signals from the previous stage of the gradation control unit (17) and directly connects them to the color channel selector (12), ye ', me'. , Ce ', ke' are not restricted by the conventional system, and are processed in the same manner as in the gradation conversion unit of the first embodiment, ie ', me', ce.
It is possible to obtain ', ke'. Then, as in the third embodiment, the image forming apparatus of the present invention is embodied with a slight improvement over the conventional system.

FIG. 8 shows an image forming apparatus according to the fifth embodiment of the present invention. In the image forming apparatus according to the fifth embodiment, the entire conventional gradation conversion unit is newly configured as the gradation conversion unit (11) of the present invention, and the gradation conversion unit (11) has a <gradation conversion formula>. I am trying to apply it.

In the embodiment shown in FIGS. 3 and 5 to 8, the image forming section is of an electrophotographic type in which an electrostatic latent image is formed on a photoconductive photoconductor by scanning with a laser beam. As a method of forming an image by the distribution of pixels,
Other techniques such as electrostatic recording and magnetic recording can be adopted.

FIG. 9 shows a method of forming a duplicate image by the electrostatic recording method. As shown in the figure, a voltage is applied to each electrode of a recording head in which a large number of electrodes are arranged in a direction perpendicular to the moving direction of a recording body made of a moving sheet-like dielectric. To form an electrostatic latent image. The process after the step of adding toner to the latent image and developing is the same as in the case of the electrophotographic system. An output unit (4) is provided for the recording head as an assembly of electrodes.
An output value (voltage value) corresponding to the image to be recorded is applied from the dot control section (14).

In the magnetic recording system (not shown), a drum body whose surface is uniformly covered with a magnetic body is used as a recording body, and an image information signal is transmitted to the magnetic recording head in contact with the surface. The magnetic recording head and the recording confronting surface are moved relative to each other while a voltage is applied to form a magnetic latent image on the recording confronting surface. Toner for the magnetic material is used for developing this latent image, but other image duplication processes are the same as those for the electrophotographic method.
By modifying the gradation adjustment unit of the conventional image forming apparatus as described above, it is possible to combine <gradation conversion formula> with other processing, and speed up and downsize by optimizing the system. And the cost performance around the system can be improved.

[0094]

The image forming apparatus of the present invention can perform color separation by integrating the gradation and the color tone by using a specific <gradation conversion formula> in the gradation conversion unit, which is the core component of the image forming apparatus. It is a thing. It was difficult in the prior art to integrate the adjustment of gradation and color tone quantitatively and rationally, which is a breakthrough point of the present invention. In the prior art, when trying to answer the needs of the color tone adjustment (color tone correction, change) of specific parts, specific portions, and even the entire image that have high market needs (high demand), the color tone adjustment is quantitative. In addition, it is impossible to produce a high-quality color duplicate image because the color tone of the part concerned and other parts are unbalanced and the tone of image combination (gradation and color tone) is distorted. It is the current situation.

On the other hand, the color separation (gradation conversion) technique incorporated in the heart of the image forming apparatus of the present invention has a specific
By adopting and operating the gradation conversion formula>, gradation adjustment and color tone adjustment can be quantified completely, color document images can be color-separated for the purpose, and gradation reproduction is reproducible. It is possible to efficiently produce a high-quality color reproduction image in which the color tone is adjusted as well as the color tone.

That is, the image forming apparatus of the present invention has the following excellent effects. (1) It is possible to rationally meet the needs for the quality of color reproduction images in the sophisticated, complicated and diversified market. (2) Production of color reproduction images, especially color separation work is quantitative,
Since it is practiced rationally, it has a remarkable effect on productivity improvement, work time reduction, efficient use of equipment, saving of consumables, and reduction. (3) In the production of color reproduction images, it is possible to pave the way to make the most of sensitivity and artistry. As a result, high added value of the image forming apparatus is realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a density characteristic curve of a color film (manufactured by Company F).

FIG. 2 is a diagram illustrating a gradation expression method.

FIG. 3 is a block diagram of an image forming apparatus according to a first embodiment of the present invention.

FIG. 4 is a diagram illustrating an outline of a basic experiment of the present invention and a color separation curve (gradation conversion curve).

FIG. 5 is a block diagram of an image forming apparatus according to a second embodiment of the present invention.

FIG. 6 is a block diagram of an image forming apparatus according to a third embodiment of the present invention.

FIG. 7 is a block diagram of an image forming apparatus according to a fourth embodiment of the present invention.

FIG. 8 is a block diagram of an image forming apparatus according to a fifth embodiment of the present invention.

FIG. 9 is an explanatory diagram of an image forming unit using an electrostatic recording method.

[Explanation of symbols]

 1 Detecting unit 2 ............ Color separation unit 3 ………… Gradation adjusting unit 4 ………… Gradation converting unit 5 ………… Color original image

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] July 23, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction contents]

[Document Name] Statement

[Title of the Invention] Image forming apparatus

[Claims]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention converts halftone (hereinafter referred to as halftone or halftone dot gradation) by gradation conversion of image information obtained by photoelectrically scanning a continuous gradation color original image. ), An image forming apparatus for producing a color reproduction image.

In particular, the present invention relates to an image forming apparatus in which a gradation converting section, which is a core component of the image forming apparatus, has a new function. More specifically, the gradation conversion unit of the image forming apparatus of the present invention does not first use the conventional density information value as the image information of the color original image, but rather of the recording medium recording the color original image. The characteristic is that the light quantity value is used to exclude the influence of the image information by the characteristic curve (the characteristic curve defined by the light quantity value incident on the recording medium and the density value formed on the recording medium). Secondly, when converting the light amount value of the color original image into gradation,
It is characterized in that it uses a specific gradation conversion formula and also has the function of adjusting the color tone during operation of the gradation conversion formula. That is, the image forming apparatus of the present invention can quantitatively and rationally control not only the gradation (also called density gradation or gradation) but also the color tone (color tone). Provided is a high value-added image forming apparatus that integrates tone and color tone adjustments.

The present invention relates to an image forming apparatus incorporating a new gradation conversion technique in which gradation (color gradation) and color tone (color tone) controls are integrated as described above. Note that the following description of the present invention is in the sense that rationalization and quantification of color tone adjustment at the time of gradation conversion, which has been difficult in the prior art, is performed.
The emphasis is placed on the fact that the gradation conversion unit of the image forming apparatus of the present invention has a new color tone management adjustment function.

[0004]

2. Description of the Related Art As is well known, a print image, a copy image (copy image), a printer output image, a TV (video) image, and the like are printed from a color original image recorded on various recording media by various color reproduction techniques. Various color reproduction images have been produced. In the production of these color duplicate images, first, the density gradation (gradation) and color tone (color tone) of the color original image are Hi-Fi color (High-Fidelity, high fidelity color) on the color duplicate image. It is a very important task to reproduce the image in the second step, and secondly, to adjust the tone having a desired tone (including both the tone and the color tone).

However, in the conventional technology, it is the current situation that the above-mentioned problems cannot be reasonably carried out with work regularity. This is a technique for faithfully reproducing the tone (gradation and color tone) of the color original image on the color reproduction image, and further for adjusting (correcting or changing) the tone of the color original image to a desired tone. , A non-linear conversion processing technique for converting image information of a color original image which is the basis thereof, particularly image information in a density region into half tone gradation (hereinafter referred to as image gradation conversion technology or image gradation conversion method). .)
This is because it does not support rational theory, and performs image gradation conversion irrationally and irrationally, relying largely on human experience and intuition.

The above-mentioned points will be described below with reference to a technique for producing a color print image which is related to the present invention and which is always required to have high quality. In the prior art, when a color print image that is a duplicate image is produced from a color film original (about 90% of the color original is a transmissive type or a transmissive type), the brightest part of the color film original ( H
Part) to the darkest part (S part) without any intention to reasonably understand the density characteristics, and the correlation between a continuous tone color film original image and a halftone dot color print image which is a duplicate image. It can be said that the setting of the "color separation curve (also called the color separation work characteristic curve, halftone dot gradation characteristic curve, etc.)" that determines is completely dependent on human experience and intuition.

Generally, a color print image is produced by using a color film original image (hereinafter, simply referred to as a color original image) with a color scanner.
color separation by r), and multicolor platemaking (generally C
The four editions of edition, M edition, Y edition, and BL edition are considered as one set. )
Then, the halftone dot color print image is reproduced. As is well known, the C plate (cyan), the M plate (magenta), and the Y plate (yellow) are color-reduced corresponding to R (red), G (green), and B (blue) of the additive method. It has a complementary color relationship according to the law, and the BL plate is called black or black plate.

Although the above-described color scanner is a mechatronics-type extremely expensive device, one of the major problems in the industry is that its operating rate is extremely low at about 30% on average. . The main reason why expensive color scanners and the like are in the low operation rate is the setup time (sc) for operating the color scanner.
For example, the length of the anner setup time is long, and the quality of the product obtained by the color separation work is unstable and insufficient, so that the rescan (remake) is often performed.

Considering this from a slightly technical point of view, as described above, as a tool for color separation work, although a color scanner or the like which is highly sophisticated and expensive at first glance is used, Multiple elemental technologies for disassembly work, such as color reproduction, color correction, and color correction (Color R
Evolution, Color Correc
and the conversion technology of density gradation (gradation) are not systematized consistently, and this can be said to be the main cause of the low operating rate of the color scanner.

As is well known, the masking equation (M
It has been pursued scientifically by applying the asking equation and the Neugebauer equation. However, the latter image density gradation conversion technology (this is due to the problem of what size halftone dots should be set for all pixels in a color original image) is rational. It has been left unsupported without supporting such theory, and this part is largely dependent on human experience and intuition.

Since various devices for color separation have been developed under such a condition, from the viewpoint of practicing color separation under the unified adjustment of color tone and gradation, the device itself In addition to being inexperienced in the basic design technology of, the operator's guess work and the experience and intuition of the operator are eliminated while using an expensive electronic color separation device (color scanner) that is expensive in actual work. Can't do (with
out operator evaluation, wi
out operator's guess wo
rk), it is not always possible to produce stable high-quality color printed images.

In particular, when the color original image is not a standard original produced under appropriate shooting and exposure conditions and appropriate development conditions, for example, an overexposed overbright original, an underexposed overexposed original, a high key or a low key ( hig
For non-standard originals such as h key or low key originals, or those with color casts or faded originals, color separation work should be performed reasonably and efficiently. I can't. That is, the color separation work cannot be rationally performed on these non-standard color original images, and the low operation rate of the color scanner, the instability of the product quality, the increase in the rescan rate, etc. I have a problem.

[0013]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The inventors of the present invention faithfully reproduce the image quality of a color original image (quality evaluated by both gradation and tone) (faithfu).
In order to rationally produce a color reproduction image of half tone gradation having a desired tone (gradation and color tone) from various color original images described above, in order to rationally reproduce color reproduction Color correction (correction)
Prior to improving the technology, we have a basic understanding that the technology for converting the density gradation of each pixel of a color original image must be rationalized.

Based on the basic recognition by the present inventors, the present inventors previously proposed a method for rationally converting the gradation of a color original image based on a novel gradation conversion formula. And achieved some success (eg USP 4,924,323; US
P5,313,310; USP5,057,931; U
See SP 5,134,494, etc.).

The novel gradation conversion method previously proposed by the present inventors has a deep relationship with the gradation conversion method applied to the image forming apparatus of the present invention. Therefore, the outline of the novel gradation conversion method previously proposed by the present inventors will be described here. The gradation conversion method applied to the present invention is a further improvement on the basis of the gradation conversion method, and such an improvement is an essential technical constitutional requirement of the present invention.

In the prior art, color separation of a color original image is performed by literally separating the original image (subject, entity image, act).
ual scene, for example, if the subject is an apple, the apple itself. ) To a “recording medium” called a photographic light-sensitive material (photographic light-sensitive emulsion), and the exposure amount E is E = I depending on a predetermined exposure condition (as is well known, the intensity I of the incident light and the incident time t). It is represented by xt.)
Based on the color photographic image (color original image) recorded in step 1, the color separation work is based on the density information (the color separation work includes both the reproduction of the gradation and the reproduction of the color tone as described above). Are doing.
As is well known, a photographic density of a photographic light-sensitive material on which an object such as a still life or a person is photographed is reduced by development.
Hic density) is formed, and this becomes a medium image. The curve showing the correlation between the above-mentioned photographic density (blackening degree) and the exposure amount E of the photographic light-sensitive material is a photographic density characteristic curve (photographic density).
ty characteristic curve). This is because the vertical axis shows the photographic density (D) (D = logIo
/ I) and the horizontal axis is the logarithmic value (logE) of the exposure amount E and is displayed. In the above photographic density (D), the intensity of transmitted light I on a film or a dry plate (transparent original)
The ratio of the incident light intensity Io to the photographic paper (reflection original)
Then, the ratio of the intensity I of reflected light and the intensity Io of completely reflected light is
Needless to say, it is used.

The above-mentioned photographic density characteristic curve (hereinafter, simply referred to as "density characteristic curve") is typically a downwardly convex foot portion, a substantially straight linear portion (linear intermediate portion), and an upward convex shape. Is a complex curve with shoulders (see FIG. 1 below for this point). In the prior art, the color separation work is performed based on the density information value of each pixel of the color original image. In other words, the conventional color separation technology is constructed from the standpoint of the vertical axis (density value) of the density characteristic curve. However, the image information value (density information value) of the color original image (medium image), which is the basis of the color separation work in the related art, is not proportional to the image information value of the original image (entity image, subject, actual scene). , And is greatly influenced by the light-sensitive characteristics (density characteristic curve) of the photographic light-sensitive material (photographic light-sensitive emulsion) which is a recording medium. That is, the photographic density of the color original image which is a medium image is linearly related (the linear relationship of 45 ° of 1: 1) to the exposure amount (logarithmic value) which is the image information value from the subject (substantial image, real scene). Not what I did. It is well known that the discrimination characteristic of light and darkness in human vision is logarithmic, and humans can determine the amount of light incident on the visual system from a subject (substantial image) based on the discrimination characteristic described above. I am evaluating. Here, I feel that the gradient of the change in density is linear (natural).

As is clear from the above description, in the production of a color print image, when the color separation work is carried out by using the density value (D = logIo / I) of the medium image recorded on the photographic light-sensitive material as a clue, it becomes Since the density information value after being affected by the photosensitivity of the photosensitivity material is used, the image information value (light intensity value) obtained from the subject (real image, real scene) that is the true target of duplication is used. It's not what you're doing. Based on the above situation, the present inventors have
The image information value of the medium image which is non-linearly changed (affected) by the photosensitive characteristic (density characteristic curve) of the recording medium (photosensitive material), that is, the density, as image information when producing a color print image. Produces a printed image based on the image information value related to the light amount such as the primary (raw, primitive) exposure amount obtained from the subject (substantial image, real scene) rather than the approach using the information value The method was earnestly studied.

As a result, in the conversion of the density gradation which is primarily important in the color separation work, (1) the density characteristic curve (photographic density characteristic curve) of the photographic light-sensitive material on which the color original image is photographed and recorded. The value on the horizontal axis (logE = logI × t)) is obtained from the concentration value on the vertical axis (D = logIo / I) (hereinafter, the vertical axis is also referred to as the D axis, and the horizontal axis is also referred to as the X axis). For example, the light amount value on the X axis is obtained from the density value on the D axis of the color original image (medium image), and more specifically, from (2), on the D axis of any pixel point (n point) on the color original image. the density information value (D _n) and through the characteristic curves projected on the X-axis, corresponding image information values for exposure of the pixel (x _n)
And then (3) x _n obtained as described above
The gradation conversion formula based on the value (light intensity value) and previously proposed by the present inventors (this is exactly the same as the gradation conversion formula adopted in the present invention described later. The invention is completely different in terms of use and application of the gradation conversion formula.) When gradation conversion of an image is performed under the conditions, it has image characteristics that are faithful to a subject (real image, actual image). It has been found that a color printed image of excellent quality is produced.

The gradation conversion technique previously proposed by the inventors of the present invention is, as is apparent from the above, the first meaning in producing a color print image of halftone dots. It is applied for the gradation conversion, which is important in particular. That is, the gradation conversion technology proposed by the present inventors has a fidelity of 1: 1 for the density gradation of various original images including color original images, and the human vision It is used to produce color reproduction images with natural gradation. The gradation conversion technology described above is not limited to standard color original images, but also non-standard originals (overexposed or underexposed, high-key or low-key originals, color fog or fading). However, it is useful for reproducing the density gradation that the subject (substantial image) is recognized to have (or originally recognized to have). In addition, it was confirmed that the tone conversion technology described above can reproduce a rich tone of color (color tone) based on faithful reproduction of density gradation.

However, as described above, the gradation conversion technology previously proposed by the inventors of the present invention is as follows. Firstly, the gradation conversion is emphasized in the color separation work. Emphasizing realization of density gradation Hi-Fi conversion (conversion of gradation with a high fidelity of 1: 1 between a continuous gradation original image and a halftone dot reproduction image) It was confirmed that the gradation conversion technology can perform the gradation conversion with high fidelity and rationally, and that the tone can be reproduced richly along with the gradation conversion.

By the way, the market needs for the quality of the color print image are not limited to the need to reproduce the color print image having the tone (gradation and color tone) according to the color original image, and become more sophisticated, complicated and diversified. It is coming. For example, a specific part (person, ceramics,
Clothes, furniture, wood products, paintings, etc.) or specific parts (areas) such as colors (colors and color tones) should be emphasized and reproduced, or the overall color tone should be blue, dark green, or light. There is a need to change to green, pink, sepia, etc. as desired. When responding to these needs, for example, when using the conventional color correction technology, the tone of the entire image is distorted even if the color tone of a specific portion or a specific portion (region) can be reproduced as required. The problem is that the image quality is severely deteriorated and the above-mentioned needs cannot be satisfied. Needless to say, in order to meet the above needs, gradation and color tone conversion technology that makes both the tone of a specific portion or a specific portion (region) and the tone of the entire image look natural to human vision. It is important to establish

In order to meet the above-mentioned sophistication and complexity of market needs, it means that in the color separation technology, the gradation conversion technology and the color tone adjustment technology must be unified (integrated). It is a thing. In that case, the point to be noted is, for example, in the case of a color print image, the halftone dots forming the color print image (basic elements for image representation).
Always has a direct relation to both gradation and color tone or density and color. This is natural because the image quality is determined by the size of the halftone dot (defines the density gradation) and the colored ink applied on the halftone dot (defines the color tone). . Then, the present inventors have established means for reasonably adjusting and managing the size of halftone dots (halftone dot% value) in the previously proposed gradation conversion technique. Therefore, the inventors of the present invention are keenly aware that the integration of the gradation adjustment technology and the color adjustment technology described above is an extension of the gradation conversion technology previously proposed by the inventors. Considered.

As a result, the inventors of the present invention have adopted the tone conversion formula, which is the core of the previously proposed tone conversion technique, and combined this with the idea of color tone adjustment. We have found that both gradations can be adjusted and managed rationally. The present invention has been completed based on the above knowledge, and with the technical similarities found between a color scanner and an image forming apparatus for producing a color printed image in mind. INDUSTRIAL APPLICABILITY According to the present invention, it is possible to adjust a color tone to a desired one within the rich gradation reproducibility which is difficult to achieve by the color separation technique, particularly the conventional technique, which adjusts and manages both the color tone and the gradation reasonably. There is provided an image forming apparatus incorporating the color tone management adjustment technology.

[0025]

The present invention will be summarized as follows.
The present invention relates to an image forming apparatus for producing a halftone (halftone) color duplicate image by performing gradation conversion on image information of a continuous gradation color original image by a gradation conversion unit of the image forming apparatus. The conversion unit is (1). A gradation conversion mechanism for converting continuous gradation to halftone (halftone), wherein the gradation conversion mechanism comprises:
(1) -1. Characteristic curve of a recording medium on which a color original image is recorded [The relationship between the light amount value (x value) incident on the recording medium and the density value (D value) formed on the recording medium is expressed by a Dx orthogonal coordinate system. The characteristic curve defined by
Function to obtain the light intensity value (x value) from (value), and (1)-
2. The light amount value (x value) is gradation-converted using the following <gradation conversion formula> to obtain a gradation intensity value (y _n value), and further, (2). A color tone adjusting mechanism for adjusting a color tone at the time of the gradation conversion, wherein the color tone adjusting mechanism is (2) -1. A color tone management point (M ₁ ) for managing the color tone of the color reproduction image is set at a desired portion between the H portion (the brightest portion) and the S portion (the darkest portion) of the color original image, and (2)- 2. At the color tone management point (M ₁ ), the color tone adjustment condition is a tone intensity value of a desired color plate (C plate, M plate, Y plate, and BL plate) used for producing a color reproduction image. Is set, and (2) -3. When the gradation intensity values set in advance in the H part and the S part of the color plate are set, (2)-
4. Light intensity value in the color tone control point (M _1), tone intensity value of each color plate for reflecting the color tone of the adjustment condition of the color tone control point (M _1), and presetting the H section and the S section of each color plate the desired The gradation intensity value of the above is substituted into the following <gradation conversion formula> to determine the γ value, and the light intensity value of the pixels from the H portion to the S portion of each of the color plates is converted into the gradation intensity value (y _n value). A function of preparing a <gradation conversion formula> for gradation conversion, and (2) -5. A function of operating the <gradation conversion formula> for each color plate for which the γ value is determined, performing gradation conversion of the light amount value of each pixel for each color plate received from the color original image, and managing and adjusting the color tone. An image forming apparatus having both the gradation converting mechanism and the color tone adjusting mechanism, characterized in that <Gradation conversion formula> y _n = y _H + [α (1-10 ^−kx ) (y _S −y _H ) / (α−β)] In the above <Gradation conversion formula>, the meaning of each symbol is as follows. is as follows; _x: shows the _(x n -x _H). That is, the color similarly obtained from the light quantity value (x _n ) corresponding to the density information value (D _n ) at an arbitrary pixel point (n point) of the color original image obtained by using the characteristic curve of the recording medium. The basic light quantity value obtained by subtracting the light quantity value (x _H ) corresponding to the density information value ( _DH ) of the H portion of the original image is shown. y _n : gradation intensity value set to a pixel on the color reproduction image corresponding to an arbitrary pixel point (n point) on the color original image. y _H : Gradation intensity value preset in the H portion of the color reproduction image corresponding to the H portion of the color original image. y _S : Gradation intensity value preset for the S portion on the color reproduction image corresponding to the S portion on the color original image. α: Surface reflectance of an image representation medium for recording a color reproduction image. β: Numerical value determined by β = 10 ^−γ . k: Numerical value determined by k = γ / (x _S −x _H ). However, x _S represents a light amount value (x _S ) corresponding to the density information value (D _S ) of the S portion of the color original image obtained by using the characteristic curve of the recording medium. γ: arbitrary coefficient.

The technical constitution and embodiments of the image forming apparatus of the present invention will be described in detail below. The present invention provides an image forming apparatus equipped with a color separation technique that integrates both gradation and color tone as described above. However, in the following description, in view of the current situation that the prior art cannot reasonably and quantitatively adjust and manage color tones, in particular, gradation conversion, which is a core component of the image forming apparatus, is performed. Emphasis is placed on the color tone management and adjustment mechanism. First, for convenience of description, the image information and the document image will be described here. In the image forming apparatus of the present invention, as image information used for producing a color print image from a color reproduction image, image information correlated with light intensity is not adopted as image information used in the prior art. There is a major feature in adopting. Further, in the present invention, the color original image is one recorded or accumulated in a predetermined recording medium, and is also called a medium image. On the other hand, an image before being recorded or accumulated in the recording medium, that is, an object that is a true target of duplication is called a substantial image (subject, actual object, real scene). The color tone management method applied to the image forming apparatus of the present invention will be described below with reference to an example of producing a color print image.

In order to gain an understanding of the present invention, a specific color tone adjusting method will be described later in detail, and a gradation conversion technique using the <gradation conversion formula> will be schematically described. As described above, at present, a color scanner (color separation device) is very commonly used in the duplication work of a color print image, and the color separation work by the color separation device is performed by a color original image (transmission of a medium image). This is performed based on the density information value obtained from the original and the reflection original. More specifically, it is common practice to produce a color print image, and generally R, G, B from a color original image (medium image) is produced.
C based on the density information value obtained through each filter of
Plate (cyan), M plate (magenta), Y plate (yellow),
We are making a BL version (black). However, for example, when a color film (transmissive type) original image (medium image) recorded on a recording medium called a photographic photosensitive material is used as a color original image, a method of utilizing the density information value taken from the image is It has the above-mentioned limitations (defects).

On the other hand, according to the present invention, as described above,
The true target of the copy is not the image recorded on the recording medium (medium image) but the literal color original image that is the source of the medium image, that is, the subject (entity image) itself, and the image to be used at the time of duplication. The information value is based on the idea that the information value should be based on the image information value correlated with the amount of light incident on the recording medium from the subject. The above points are the basic differences between the gradation conversion technique of the present invention and the conventional technique.

This will be described below from another angle. In the color separation technique, it is necessary to convert a continuous tone color original image (for example, a transmissive color film original document) into a halftone dot color original image. A color separation curve (gradation conversion curve) defines the correlation between halftone dot images. The conventional color separation curve is formed on the D axis (density axis) of the photosensitive characteristic curve (photographic density characteristic curve defined by the D axis-x axis orthogonal coordinate system) of the photographic light-sensitive material as the recording medium. It is set based on the density information value. On the other hand, the color separation curve of the present invention is set on the basis of the image information value correlated with the light quantity of the X object (substantial image) of the photographic density characteristic curve as described above. That is, it can be said that the D-axis color separation curve is used in the conventional color separation technology, whereas the present invention uses the X-axis color separation curve.
The two are basically different.

Next, a method of obtaining the image information value of each pixel of the color original image, that is, the light amount value in the image gradation conversion method using the <gradation conversion formula> of the present invention will be described.
First, from a characteristic curve of a photographic light-sensitive material as a recording medium used for photographing a color film original image (medium image), specifically, a photographic density value (D = logIo / I) and a subject (substantial image, real scene). A density characteristic curve showing the relationship between the image information value correlated with the amount of light incident on the photographic light-sensitive material as the recording medium, that is, the logarithmic value of the exposure amount (E = It) is prepared. Next, an arbitrary pixel (n
To determine light intensity values density value from (D _n) via the characteristic curves of the point) the (x _n), it is a function of the characteristic curves. For this purpose, for example, a density characteristic curve corresponding to the recording medium provided as a technical material by a photographic light-sensitive material manufacturer may be made into a function. If it can be reasonably functionalized, D
The D _n value on the axis can be easily converted to the x _n value on the x axis. Figure 1 shows the concentration characteristic curve (F company, Fujichrome)
Is shown. Further, Table 1 shows the result of formulating the concentration characteristic curve of FIG. In addition, as shown in Table 1, in order to formulate the concentration characteristic curve as accurately as possible, the formulating section is set to 8 sections, and the formulating is attempted in each section. It goes without saying that the more functional divisions, the more accurate the functional formula can be obtained.

[0031]

[Table 1]

In the mathematical expression of the density characteristic curve, an image information value correlated with the scale of the D axis indicating the density value of the color original image (medium image) and the light amount indicated by logE of the subject (substantial image). Assuming that the scales on the X-axis indicating the are the same, a function that defines the correlation between D and x was obtained. This is a kind of imitation made from the following viewpoints, and the present inventors consider that it is rational.
In this sense, the term canonical value is used on the X axis of FIG. That is, originally, in the photographic density characteristic curve, the logarithmic value of the exposure amount E on the X axis logE = logI ×
t) is located, which corresponds to the fact that the discriminative property for light and darkness of the visual sense is logarithmic as well as the perception of the density (visual sense) of the D axis, and thus the imitation on the above scale is reasonable. I think that is. It is needless to say that the above-mentioned grading in the present invention is a kind of simple method and is not limited to this.

In the present invention, the density value (D) of the color original image (medium image) formed by photographing and recording the subject (substantial image) on the recording medium (photosensitive material) as described above.
_n value) rather than based on, is to subject (entity image) correlated image information value to the amount represented by the X axis to be incident on the recording medium from the (x _n values) based. As described above, as the concentration characteristic curve is shown in Table 1, the D _n value and the x _n value are correlated by the functional formula of x = f (D). Therefore, it is easy to change the D _n value from the x _n value. You can ask.

Next, the gradation conversion technique of the present invention uses the light quantity value (x _n value) obtained as described above and the <gradation conversion formula> to perform a color separation curve (gradation conversion curve). That is, it suffices to obtain an x-axis color separation curve that replaces the conventional D-axis color separation curve and perform tone conversion of the image. That is,
In the case of producing a color print image, an image information value (x that correlates from the density value (D _n ) at an arbitrary pixel (n point) on the original image to the light amount of the corresponding pixel under a predetermined density characteristic curve. _n ) is obtained and the (x _n ) value is substituted into the <gradation conversion formula> to calculate the gradation intensity value (y _n ), that is, the halftone dot area% value (y _n ). Then, the gradation intensity value (y _n ) (halftone dot (area)% value) may be input to the output unit (halftone dot generator, dot generator) of the color scanner to produce a color print image.

The above-described <gradation conversion formula> derivation process of the present invention will be briefly described here. Halftone dot% value (y _n ) used when producing a color print image having the above-mentioned halftone dot gradation
<Gradation conversion formula> is a generally accepted density formula (photographic density, optical density), that is, D = logIo / I = logI / T Io = incident light amount I = reflected light amount or transmitted light amount T = I / Io = It is derived from the reflectance or the amount of transmitted light. The general formula for the density D described above is applied to plate making / printing as follows. Density (D ') in plate making / printing = log (Io /
I) = log unit area × paper reflectance / [(unit area−
Halftone dot area × paper reflectance) + halftone dot area × ink surface reflectance] = log αA / [α {A- (d1 + d2 + ...
dn)} + β (d1 + d2 + ... dn)] where: A: unit area dn: area of each halftone dot within the unit area α: reflectance of printing paper β: surface reflectance of printing ink.

The present invention is based on the density formula (D ') relating to plate making and printing, and a basic density value (x) at an arbitrary sample point (pixel) (n point) on a continuous tone color original image, In order to associate the theoretical value with the actually measured value in association with the halftone dot% value (y _n ) of the halftone dot in the sample points on the color print image of the halftone dot corresponding to this, the above <gradation conversion formula> Is derived.

[0037] In operation of the <tonal conversion formula> of the present invention, in general, 5% _{y H} in C plate, 95% _{y S,} 3 percent _{y H} in M plate and Y plate, a _{y S} 90 Halftone dot%
The value is used. In the operation of the <gradation conversion formula>, if a densitometer measurement value is used for the density value and the above-mentioned percentage numerical values (% values) are used for y _H and y _S , the y _n value also becomes a percentage numerical value ( % Value).

In the operation of the <gradation conversion formula> of the present invention, it is possible to use it by modifying it as follows as well as using it by arbitrarily processing, deforming or guiding it. y _n = y _H + E (1-10 ^−kx ) · (y _S −y _H ), where E = 1 / (1−β) = 1 / (1−10 ^−γ ), α = It is one. This is one in which the surface reflectance of the printing paper (base material) used for expressing a color printing image is 100%. The value of α may be any value, but may be 1.0 in practice. This also applies to intensity images such as video images.

Further, according to the modification (alpha = 1.0), a _{y H} in the brightest part (H portion) of the color print image, as was expected a _{y S} to darkest part (S unit) It can be set, which is a great feature of the present invention. By the definition, the above-mentioned point is that x = 0 in the H portion on the color print image, and x = x _S in the S portion.
It is clear from the fact that −x _H is obtained, that is, −k · x = γ · (x _S −x _H ) / (x _S −x _H ) = − γ. Thus, the present invention <
By using the gradation conversion formula> (a modification of a = 1), it is possible to always set the y _H value and the y _S value as scheduled in the H portion and the S portion on the color print image. This point
This is a very important point for users to evaluate and consider the work results. That is, y _H and y _S in the color print image
Set the desired value to and change the γ value (however,
= 1.0), various x-axis color separation curves (gradation conversion curves) can be obtained. Then, the image quality content of the color print image produced under these x-axis color separation curves can be easily evaluated in relation to the γ value.

X of each color plate for multicolor plate making (generally, four plates of C plate / M plate / Y plate / BL plate are used) utilizing the <gradation conversion formula> of the present invention. To set the axis color separation curve (gradation conversion curve), the following may be done.
In the industry, it is common practice to first set a reference C color separation curve (gradation conversion curve), and then set the other color plates so that the gray balance and color balance are maintained. Is. The maintenance of the gray balance described above is a condition for reproducing a neutral density (gray) by three color plates (C / M / Y plates) and is a main requirement. In the industry, standard values shown in Table 2 below are generally adopted in order to maintain the gray balance. In Table 2, M ₁ is a gray balance management point (hereinafter, also referred to as an intermediate point) set in the intermediate portion of the dynamic range (density area) of the H portion to the S portion. In the art, the M ₁ point is usually set at a dot% value of C plate of 50% as shown in Table 2.
The main reason for setting the M ₁ point to the halftone dot 50% value of the C plate is that it is widely recognized that the halftone dot% value region is a reproduction region with rich gradation. From Table 2, in the industry, in the M ₁ point (halftone), the halftone dot value of the C plate is set to 50%, and the halftone dot value of the other color plates (M / Y plate) is 40%. It is understood that the gray balance (neutral density) is maintained by setting to. Needless to say, it goes without saying that the standard value can be changed depending on the characteristics of the ink used.

[0041]

[Table 2]

As described above, the gradation conversion technique of the present invention is
In producing a color print image, the density information value (D _n ) obtained from a color original image (medium image) is not used, but is incident on a recording medium for forming a medium image from a subject (substantial image). It is premised that the image information value (x _n ) correlated with the amount of light to be used is used and that the <gradation conversion formula> is used, and the color has gradation characteristics that are faithful to the subject (substantial image). It is possible to produce a print image, and further, a color print image in which gradation characteristics are changed to a desired one, with work regularity, universality and elasticity.

Next, the core technical constitution of the present invention, that is, incorporating the tone adjustment technique into the above-mentioned tone conversion technique, in other words, integrating the tone conversion technique and the tone management adjustment technique Will be described. The occasion for the integration of the gradation and the color tone described above was as follows. (1) The <gradation conversion formula> proposed by the present inventors and used also in the present invention is, as described above, the halftone dots of all pixels from the H portion to the S portion of the color print image. The dot value (dot size) of (dots) faithfully reproduces the gradation characteristics of the color original image, and the gradation is natural to human vision. It is an important tool for adjusting to the characteristics. (2) The halftone dot value set for each pixel always has a direct relationship and influence on both gradation and color tone (or density and color). (3) Market needs include not only 1: 1 reproduction of color original images (Hi-Fi reproduction), but also enhancement, change, or correction of the color tone (color tone) of a specific portion or a specific portion (area) of the image. The number of cases of demand (demand) is increasing. In addition, in the above request, customers and designers have color charts owned by them.
Hart, which will be described later in detail. ), The content of the request is presented and specified by the halftone dot value. (4) When the above needs are met by a conventional color separation technique, in particular, a conventional color correction (color correction), even if the color tone of a specific portion is approximated to the requested content, the tone (gradation) of the entire image is The color tone is distorted, and the value as a product is often lost.

The color chart (color cha)
rt) is a basic scale (reference table) for color reproduction in which all colors are expressed by halftone density gradations using the printing process 4 primary color inks. For example, “DIC GRAF-G” issued by Dainippon Ink and Chemicals, Inc.
"Color chart" (March 1991). In the color chart, there are various combinations as shown below as combinations of each color plate for color reproduction. 1. Basic combination: C (cyan) and M (magenta)
There is a chart based on the combination of. For example, (C) is printed on the vertical axis and (M) is printed on the horizontal axis in 12 gradations with halftone dot% values of 0 to 100% to form a basic pattern. There is a structure in which Y (yellow) and BL (sumi) having a% value are printed and overlapped. As Y or BL of the constant halftone dot% value, Y = 10
%, BL = 10%, Y = 10%, BL = 30
%, Y = 50%, BL = 10%,
and so on. 2. Other combinations: (1) A combination of (Y) on the vertical axis and (M) on the horizontal axis,
(2) A combination of (C) on the vertical axis and (Y) on the horizontal axis,
(3) A combination of (BL) on the vertical axis and (Y) on the horizontal axis, (4) A combination of (BL) on the vertical axis and (M) on the horizontal axis, (5) Vertical axis (C), a combination of (BL) on the horizontal axis.

As described above, the color tone on the color chart is specified by the halftone dot% value of each color plate (C / M / Y / BL). Therefore, in response to a color tone change request from a customer or a graphic designer based on the color chart, a technology for quantitatively and rationally managing and adjusting all halftone dot% values of each pixel is used as a color separation technology. It goes without saying that we must secure it.

From the background described above, the present inventors have
The gradation conversion formula> has the ability to completely quantitatively and reasonably manage and adjust the halftone dot value of all pixels from the H point to the S point, and is therefore effective for adjusting the color tone. I thought it would be a powerful tool. This is an opportunity to develop a color separation technique that integrates gradation and color tone using the <gradation conversion formula> as a main tool.

As described above, the image forming apparatus of the present invention incorporates the color separation technology in which the gradation adjustment and the color adjustment are integrated into the gradation conversion unit which is the core component thereof. It has characteristics. In particular, in the present invention, the color separation technique incorporating the color tone management adjustment is significantly different from the conventional technique, and this point will be described below.

1. First, a color tone management point (M ₁ ) for managing the color tone of the color reproduction image is set at a desired portion between the H portion and the S portion of the color original. In the present invention, the same symbol (M ₁ ) as the halftone point (M ₁ ) for maintaining the gray balance in Table 2 is used as the symbol of the color tone management point (M ₁ ). This reflects that the tone reproduction in the halftone region is an important point in the color separation technique, and thus is also important in the tone reproduction. It is needless to say that the color tone management point (M ₁ ) is not limited to the halftone point for maintaining the gray balance described above, and may be a desired point between the H portion and the S portion. .
The color tone management point (M ₁ ) displays a vertical axis (y-axis: halftone dot% value) and a horizontal axis (x-axis: light amount value), as will be described later in an example and in FIG. .) Cartesian coordinates are displayed as light amount values on the horizontal axis (X axis). In addition,
Since the light quantity value correlates with the density value of the color original image, it may be displayed as the density value.

2. Next, at the color tone management point (M ₁ ) designated as described above, the color tone adjustment condition is determined by the halftone dot% value of the desired color plate (C plate, M plate, Y plate, and BL plate). To do. The specific content of the adjustment (change) condition of the color tone is as described in the description of the color chart.

3. The next step is to use each of the color plates (C plate, M plate, Y plate, BL
Preparation of the color separation curve (gradation conversion curve) used for producing the color separation image of (version), more specifically, the <gradation conversion formula> for setting the color separation curve for each color plate. Preparation. By the steps (1 to 2), the light quantity value of the color tone management point (M ₁ ), for example, M ₁
= 0.400, · Color tone adjustment conditions, for example, in the color tone management point (M ₁ ), C plate halftone dot% value (50%), M plate halftone dot% value (20%), Y plate halftone dot% A value (10%) and a halftone dot value for BL (10%) are set. The halftone dot% values (y _H , y _S ) set in the H and S parts of each color plate are set to values given in advance or desired values. The y _H value and the y _S value given as the above-mentioned conditions are, for example, 5% for the C plate, respectively, as described in the description regarding the operation of the <gradation conversion formula> of the present invention. And 95%, M version and Y
For plates this means standard values of 3% and 90% respectively (see Table 2). Under the above conditions, the operating condition of the <gradation conversion formula> used to set the color separation curve for each color plate, that is, the γ value of the <gradation conversion formula> is determined. For example, the γ value of the <gradation conversion formula> for setting the color separation curve for C plate is determined as follows. In the above <gradation conversion formula>, x _H = 0.00, x _S = 1.00, x _n = M ₁ = 0.4
0, α = 1.00, y _H = 0 (%), y _S = 95
By substituting (%), y _n = 50% and solving, a value of γ = 0.45 is obtained. As a result, <gradation conversion formula> for setting the color separation curve for C plate is prepared. The same applies to other color plates.

4. The next step is the γ value (γ =
0.45), using the <gradation conversion formula>,
This is a step of gradation-converting the light quantity values (x _n ) of all pixel points (n points) reaching the H part and obtaining a color separation curve (gradation conversion curve) for the C plate. In other words, the color separation work is performed using the <gradation conversion formula> for the C plate in order to produce the C plate color plate image. The same applies to other color plates.

With respect to the image forming apparatus of the present invention, particularly the characteristics of the gradation converting section which is the central mechanism (main component), the gradation converting section of the color scanner for producing a color print image is taken as an example. Explained. However,
The image forming apparatus of the present invention is not limited to a color scanner for producing a color print image for the following reason. As is well known, various methods are known as a method of expressing a halftone (halftone) gradation pixel. For example, a method of changing the pixel coverage by the size of a dot (also called a size modulation method. This method is found in monochrome and color scanners for producing printed images, piezoelectric ink jets, etc.) or a regulation. A method of changing the pixel coverage by the number of dots of the same size (also called a density modulation method. This method is found in thermal fusion transfer). A method of changing the density (also called a direct density modulation method. This method is found in thermal sublimation transfer. In addition, a TRT composed of a CRT or liquid crystal that forms a pixel by adjusting the brightness of the pixel.
V receivers are also included in this category. ).

The above-described gradation conversion method of the present invention is applied to an image forming apparatus that employs the above-described various pixel expression methods. That is, the image forming apparatus of the present invention includes devices that adopt the above-described various pixel expression methods. In other words, the image forming apparatus of the present invention should be construed in the broadest sense, and can reproduce color reproduction images such as copying machines, printer machines, plate making machines, image transmission machines, TV imaging machines, and electronic camera machines. Everything with manufacturable functions is targeted.

In each of the various image forming apparatuses described above, y obtained by the arithmetic processing of the <gradation conversion formula> of the present invention.
_{If the n-} value (gradation intensity value) is made to correspond to the gradation display method (variable dot method, constant dot method, variable density dot) or luminance display method suitable for each image forming apparatus, a color reproduction image can be produced. Needless to say, it is a good thing. For example, as shown in FIG. 2, in the case of the column of FIG. 2A, the distribution of pixels recorded in a given pixel block is mutually dispersed in the pixel block as the number of pixels recorded increases. It takes a positional relationship. In addition, for example, it may be considered that the pixel blocks are sequentially expanded outward from the central portion in a spiral shape, and in that case, the dot approximates to the halftone dot adopted in the photolithography. The row in FIG. 2B is the same as that in FIG.
Halftone dots having an area corresponding to the number of pixels in the column (a) are shown. Although the pixel block has been described as a 4 × 4 matrix type here, 17 gradations are expressed by this. In general, an n × n matrix type pixel block expresses n ² +1 steps of gradation (0 to 100%). A method of expressing the gradation of a continuous gradation original image by the distribution of pixels formed by the matrix type pixel block is generally called a dither matrix method and is well known in the art. .

The image forming apparatus of the present invention has the greatest feature in the color separation technique incorporating the gradation (gradation) conversion and the color tone (color tone) adjustment function in the gradation converter. Here, other features will be described below.
The image forming apparatus of the present invention uses various color original images, that is, various color original images obtained by recording, photographing, or image-converting a subject (substantial image) on a desired recording medium using information transmission media such as light and electromagnetic waves. Images (medium images) can be used. Examples of the recording medium for the color original image include a transmission type color film (photosensitive emulsion), a photoelectric conversion element such as a two-dimensional CCD or a photodiode, an optical disk or a porcelain disk. It goes without saying that a reflection original such as a painting or a color print can be used as the color original image.

In order to obtain the light amount value from the density information value in the various recording media described above, a characteristic curve of the recording medium, such as a photographic density characteristic curve or a photoelectric conversion characteristic curve, may be used. For reflection originals such as paintings and color prints, the characteristic curve corresponds linearly with the density information value and the light amount value of 1: 1 (corresponding to a linear relationship of 45 °). Needless to say, that is all right.

As will be shown in the embodiments described later, the present invention is applicable to various recording media such as photodiodes and CCDs that constitute the above-mentioned recording media system and has a characteristic density characteristic curve (or photoelectric characteristic) of these recording media. By defining the conversion characteristic curve), it is possible to provide a high value-added image forming apparatus based on the performance of the existing recording medium. In other words, using these existing recording media, it is possible to produce a color reproduction image having a tone (density gradation or color tone) that is far superior to the conventional one. That is, in the industry, in order to produce a high quality color reproduction image,
Although efforts are being made to improve the characteristics (photosensitive characteristics and photoelectric conversion characteristics) of various recording media (for example, to increase the dynamic range and to ensure the linearity of characteristic curves), the present invention produces a color reproduction image. In this case, it is not always necessary for the various recording media to have high quality and high performance, and existing performances (characteristics) are sufficient. This is due to the gradation conversion technology incorporated in the image forming apparatus of the present invention, and constitutes another major feature of the present invention.

Next, in the image forming apparatus of the present invention, the gradation for performing color separation by integrating the above-mentioned gradation (gradation) and the adjustment of color tone (color tone), which are the main constituent elements (mechanism) thereof, The configuration of the conversion unit will be described. 1. In the present invention, the gradation conversion unit can be configured as follows, for example. (1) An image in which a density information value obtained from a color original image recorded on a predetermined recording medium (sensor) and a light amount value incident on the recording medium (sensor) from an object (real image, real scene) are correlated An image information value and / or an image information electric signal value (even in analog) relating to the density of a color original image (including a hard original and a soft original) based on a characteristic curve that defines a correlation between the information value and A mechanism (software compatible) for obtaining an image information value correlated with the amount of light corresponding to either digital or digital), and (2)
A mechanism (software compatible) for operating the <gradation conversion formula> is provided.

2. Further, the configuration of the output unit is such that the current value and voltage value of the recording unit (recording head) of the device are associated with the calculated value by the <gradation conversion formula>, that is, the y _n value (gradation intensity value),
Alternatively, by controlling the application time, etc., the size of dots and the array density of dots are changed (the size modulation method or the density modulation method is adopted), and the half tone (halftone dot level) in which the gradation and color tone are adjusted as desired. It is sufficient to configure so that a color duplicate image of (tone) is output. The y _n value of the present invention is a dot% in the context of the technology of color printing image reproduction technology.
Although it is also called a value, it is generally called a gradation intensity value as described above. The y _n value of the present invention should be construed in its broadest sense regardless of its nominal law.

For example, in the case of producing an original plate of a color print image which is a halftone image, that is, an original plate for printing (color plate image), an existing system well known in the art may be used, and a commercially available electronic The gradation conversion mechanism of the present invention may be incorporated in the color separation mechanism section of a color separation device (color scanner, total scanner). The image forming apparatus of the present invention can be configured using various existing image forming systems including the color separation apparatus (color scanner, total scanner) described above. More specifically, the image forming apparatus of the present invention irradiates a color film original image (transmissive medium image) with a small spot light and converts the transmitted light (image information signal) into a photoelectric conversion unit (photomultiplier). Or CCD) to convert the intensity of light into the intensity of voltage, and the resulting image information electrical signal (voltage value) is digitized in the gradation conversion unit, and the necessary gradation and processing is performed by a computer to perform gradation. A well-known existing system that creates a color duplicate image by converting and operating the output unit based on the gradation intensity value output from the computer and ejecting ink onto recording paper in synchronization with the input system. In, the gradation conversion unit is replaced by the gradation conversion unit of the present invention.

In the case of a color separation device (color scanner), a computer processing unit (gradation conversion unit) for rearranging and processing an electric signal which is image information of a color original image (medium image) is reconfigured. Then, the image information value correlated with the light amount is obtained from the density information value of the color original image (medium image) recorded on the color film (recording medium) through the density characteristic curve of the color film (recording medium), and It is only necessary to incorporate software for outputting the halftone dot% value (y _n value) in which the gradation conversion and the color tone are adjusted by using the <gradation conversion formula>.

As can be seen from the above description, in the existing system, the color original image (medium image photographed and recorded on a recording medium called a photographic light-sensitive material) is recorded by the image information acquisition mechanism (detection unit) of the image forming apparatus. Specifically, an image information value correlated with the density is obtained by being processed by a photoelectric conversion unit (photomul or CCD). Strictly speaking, since the photoelectric conversion unit has its own characteristic curve (photoelectric conversion characteristic curve), in the photoelectric conversion unit, the image information of the color original image is equivalent to that of the photoelectric conversion unit. It will be affected (altered or deteriorated) by the photoelectric conversion characteristic curve. Therefore, it is preferable to eliminate the influence of the photoelectric conversion characteristic curve, but this may be ignored.

As the software applied to the above-mentioned gradation converting unit, the image information which correlates the density information value (D _n ) which correlates with the density of the color original image with the corresponding light quantity under a predetermined density characteristic curve is used. A general-purpose computer that converts into a value (x _n ) and has the algorithm of <gradation conversion formula> as software and has an A / D (analog-digital conversion) and a D / A I / F (interface), An electrical circuit that embodies a general-purpose IC with the algorithm as logic, and an RO that holds the algorithm operation result
Various forms such as an electric circuit including M, a PAL in which an algorithm is embodied as an internal logic, a gate array, a custom IC, and the like can be taken. Particularly in recent years, modularization has been developed, and an arithmetic mechanism capable of performing gradation conversion of an image based on the above <gradation conversion formula> of the present invention is a dedicated IC, LSI, microprocessor, or microprocessor. It can be easily manufactured as a module such as a computer.

Next, the related matters for exhibiting the color tone adjusting function in the gradation converting section of the image forming apparatus of the present invention will be specifically described. In the case of an image forming apparatus, each color plate (C / C
(M / Y / BL) is not manufactured individually and is not overprinted, but each color is continuously superimposed under sequence control. However, for convenience of description, in the following description, it is called a color plate image that statically captures each color image, and in relation to this, a C plate image (color plate image), a C plate separation curve (gradation conversion curve), etc. Is used.

(1) Determination of Color Tone Management Point (M ₁ ) The color tone management point (M ₁ ) may be any point between the H section and the S section. However,
For monochrome print images or color print images,
In order to reproduce rich gradation, a halftone, more specifically, a point where the halftone dot value of a C plate image (color plate image) is 50% is widely adopted as a management point. Therefore, also in the image forming apparatus of the present invention, as the management point (M ₁ ) of the color tone, the region of the gradation intensity value (y _n value) = 50% in the C plate color separation curve (gradation conversion curve) is selected. Is preferred. The above-mentioned color tone management point (M ₁ ) is coded as a standard condition (see Table 2) for maintaining the gray balance during the production of a color print image. In the present invention, as described above, the color tone management point (M ₁ ) is
It goes without saying that the gradation intensity value (y _n value) is not limited to 50%.

(2) Light intensity value (x value) of color tone management point (M ₁ ) The light intensity value (x value) of color tone management point (M ₁ ) may be determined as follows. In each color plate of the image forming apparatus, it is preferable to set a reference color separation curve (gradation conversion curve) and set the other color plates so that gray balance and color balance are maintained in relation to this. This idea is the same as the production of a color print image. Therefore, as in the color printing technique, the reference color plate is the C plate, and (i) a desired γ value, for example, γ = 0.45 used when a color print image is produced, (ii) a desired y _H ，
y _S , α value, for example, y _H = used when the printed image is produced
0%, y _S = 95%, α = 1.00. Under the condition of <
Gradation conversion formula> is operated to set the color separation curve for C plate (gradation conversion curve). Next, in the color separation curve for C plate (gradation conversion curve) set as described above, y _n
The light quantity value (x value) at which = 50% is obtained. That is,
The above equation may be solved by substituting the above conditions into <gradation conversion equation>. In this case, a light quantity value of x = 0.40 is obtained. 50 = 0 + [( ^1-10-0.45x ) (95-0) /
(1-10 ^−0.45 )] (Note) In the operation of <gradation conversion formula>, x _S −x _H =
It was set to 1.000. In general, dynamic range of light intensity values obtained from a color original image (medium _image) (x S _-x H) is not a 1.00, here using a value obtained by normalizing the dynamic range 1.00 There is. Needless to say, even if the dynamic range is normalized to 1.00, the image quality contents change relative to each other, so there is no problem in image processing.

(3) Method for Determining γ Value for Determining Color Separation Curve for Each Color Plate (C / M / Y / BL) As described above, the color separation curve for C plate (gradation conversion curve)
The γ value for setting γ = 0. It is set as 45. For other color plates, γ for setting each color separation curve according to the content of the color tone adjustment conditions.
You have to ask for a value. For example, in the case of the M plate, the tone intensity value (y _n value) of the M plate is 20 at the color tone management point (M ₁ ) (the light amount value at the color tone management point is x = 0.40). %, And the gradation intensity value as an initial condition is 0% to 68% (the gradation intensity value of the y _H part (0
%), When the gradation intensity values of y _S portion (68%)), the substituted into <gradation conversion formula> Request γ value for M plate. That is, γ = 0.20 is obtained from the following formula. 20 = 0 + [(1-10- ^{γ (0.40)} ) (68-
0) / (1-10 ^−γ )] In the image forming apparatus of the present invention, the light intensity value at the color tone management point (M ₁ ) and the γ value for each color plate are automatically calculated, and desired color separation is performed. Software for preparing a curve may be installed in the gradation conversion unit.

[0068]

The image forming apparatus of the present invention will be described in more detail with reference to the drawings. FIG. 3 is a block diagram of the image forming apparatus according to the first embodiment of the present invention. As shown in FIG. 3, in the image forming apparatus of the present invention, the transmitted light or the reflected light of the color original image is converted into R (red), G (green), and B (green).
A detection unit (1) for spectrally reading (blue) and output signals of the detection unit (1) are C (cyan), M (magenta), and Y.
(Yellow), K (Black) (hereinafter BL as a symbol
Use K instead of. Color separation signal (2) for converting into a color separation signal and gradation adjustment for processing the color separation signal so that an appropriate gradation image is produced by using the above-mentioned <gradation conversion formula> of the present invention. The unit (3) and the output unit (4) for exposing the electrophotographic photosensitive member with a laser beam based on the output signal of the gradation adjusting unit (3). In addition, as shown in the figure, the laser beam output from the output unit (4) is a high-speed rotating polygon mirror (a polygon mirror).
A latent image is formed on the photoconductor (b) by being polarized by (a), the latent image is developed in the developing section (c), and further, a transfer drum (a transfer cylinder) (d).
The image is transferred to a recording sheet supplied by and is fixed by the fixing unit. In order to form a color image, an independent photoconductor and a developing unit are provided for each of the component colors, and the toner images formed are sequentially transferred to a recording sheet, or the components of one photoconductor are provided. A process of forming a latent image of color, developing it into a toner image, and then transferring it to a recording sheet is repeated for each color component.

In the present invention, among the four blocks,
The detection unit (1), the color separation unit (2), and the output unit (4)
The mechanism and configuration generally adopted in the conventional image forming apparatus are used as they are. In other words, the gradation adjusting unit (3) is the object of the improvement of the present invention. Strictly speaking, the gradation (gradation) of the present invention is
n) and the gradation conversion unit based on the above <gradation conversion formula> which performs color separation by integrating adjustment of color tone (color tone) is also related to improving the function of the color separation unit (2). Is. Therefore, the image forming apparatus of the present invention is configured by using the color separation unit (2) of the existing image forming apparatus and changing the configuration of the conventional gradation converting unit to the gradation converting unit of the present invention. It can be said that

The structure of the image forming apparatus of the present invention will be specifically described below. The detection unit (1) detects the transmitted light or the reflected light of each part of the color original image (5) by a photoelectric conversion element such as a photomultiplier, and detects R, G, B, and USM signals as current values. Is output, and this signal is converted into a voltage signal in the A / V converter (6). The color separation unit (2) logarithmically calculates the respective voltage signals of R, G, B, and USM of the detection unit (1) in the log amplifier (7) to convert the signals into concentrations, and basic masking (BM)
In (8), the C / M / Y color components (basic color components) are separated and the black (K) component is separated. That is, in the image forming apparatus of the present invention, a color original image (5) which is an object to be reproduced (color print, color printed matter, etc.) is first detected by a photomultiplier or solid-state image sensor (CCD) in the detection unit (1) by a conventional method. Image information for each color (R, G, B) is detected by an image information reading mechanism configured by, and the density information value (for producing a color duplicate image by color separation in the color separation unit (2) ( D _n ) is obtained. This is obtained for each color (C, M, Y) component (basic color component) as described above.

In the present invention, the density information value (D _n )
Is a characteristic curve of the recording medium system, for example, CC which is the recording medium.
It goes without saying that the photoelectric conversion characteristic curve of D is used to convert the image information value (x _n ) correlated with the light amount, and further to the basic light amount value (x). In addition, in _order to obtain the image information value (x _n ) correlated with the above-described light amount, it may be performed by software or hardware not shown. In the present invention, the function of obtaining the image information value (x _n ) and the basic light amount value (x) correlated with the light amount from the density information value (D _n ) is incorporated in the gradation adjusting unit (3) described below. It can be done. This is because the gradation adjusting unit (3) operates an algorithm of <gradation conversion formula>, and the image information value (x _n ) correlated with the light quantity is also obtained by a predetermined algorithm, so that the calculation function It is based on the idea of putting together. Needless to say, the present invention is not limited to this method.

FIG. 3 shows a color correction (CC) section (9) as a structure of the color separation section (2). Here, for each original color of R, G, B and C, M, Y, C
Component, M component, and Y component are controlled, and the K component of the original document is added to the UCR (unde) of the UCR / UCA section (10).
r color removal), or UCA (u
ncer color addition)
The ratio represented by the three types of inks of C, M, and Y and the ratio represented by K (black ink) are determined.

In this way, the C, M, Y and K components converted into the image information value correlated with the light quantity are converted into the gradation conversion unit (1
In 1), conversion from C, M, Y, K to pixel density values (gradation intensity values) in pixel blocks of each color component, that is, ce ', me', ye ', ke' indicating the effective area ratio of each color component. Do. The gradation conversion unit (11) uses the characteristic curve of the recording medium on which the color original image is recorded, and uses the characteristic value (D _n ).
It has an algorithm for obtaining the light quantity value (x _n ) from the above, and a calculation algorithm of <gradation conversion formula>. Then, by applying the <gradation conversion formula> to each of C, M, Y, and K, the effective area ratio of each color component, ce
Find ', me', ye ', ke'.

As the gradation conversion unit (11), a general-purpose computer having an algorithm of <gradation conversion formula> as software and having an I / F (interface) of A / D and D / A, an algorithm is a logic. Can take various forms such as an electric circuit embodied by a general-purpose IC, an electric circuit including a ROM holding a calculation result of an algorithm, a PAL embodying an algorithm as internal logic, a gate array, a custom IC, and the like.

The effective area ratio corresponding to the pixel density value (gradation intensity value) of each color component obtained by the gradation conversion unit (11) is input to the color channel selector (CHS) (12), and the color channel selector (CHS) (12)
Outputs ce ', me', ye ', and ke' in sequential selection. This output is A / D converted by the A / D converter (13) and input to the output unit 4. That is, each color is input to the dot control (D / C) unit (14).
The dot control (D / C) section (14) controls the output value of the laser beam generator (15).

<Basic Experiment> Next, in the image forming apparatus of the first embodiment of the present invention described above (see FIG. 3), the core gradation conversion unit (11) is used to reproduce the gradation (gradation) of the color reproduction image. ) And tones (color tones) are integrated and adjusted. Especially,
In order to confirm whether the color tone can be adjusted rationally while maintaining the gradation, a basic experiment was conducted in the following manner. Since this is a basic experiment, only the color plate (C / M / Y plate) was tested, and the BL (K) plate was not used. (1) Color original image As a color original image, a brown ceramic jar (transparent original) which is a standard original (an original having a standard image quality) was used. (2) Design material for each color plate Table 3 shows the design material for each color plate for the management adjustment of the color tone as a basic experiment. (Note 1) In Experiment A, the tone intensity value (y _S ) of the S portion was specified first, and then the tone intensity value of M ₁ point (color tone control point) was calculated by the following formula (1) and the experiment was conducted. It is one. In addition,
The standard values of the following formula (1) are shown in Table 2. M ₁ point dot% value = (standard value of _{M 1} point) × (tone intensity value specified in the S portion) / (standard value of the S portion) ......... (1)
(Note 2) In Experiment B, the value of Experiment A was adopted as the gradation intensity value of M ₁ , and the standard value (Table 2) was adopted as the gradation intensity value of S part. (Note 3) Since the catch light portion is selected as the H portion of the color original image (pot), the halftone dot% value of the H portion of all color plate images is "0".

[0077]

[Table 3]

The four basic experiments [Experiment A (N
o. 1 to No. 2) and Experiment B (No. 1 to No.
The results of 2)] were all as expected in the light of experience. This indicates that the color tone management method using the <gradation conversion formula> of the present invention is rational. The contents of the four color reproduction images obtained from the basic experiment are as follows. (1) At all four points, the gradation (density gradation) is well reproduced in the entire dynamic range of the H to S parts, and the halftone volume feeling is also suitable for human vision. (2) The color tone of the vase is blue in Experiment A (No. 1 to No. 2), blue in the halftone region in Experiment B (No. 1 to No. 2), and the original image in S part. It was a brownish street. It should be noted that these color tones are exactly the same as in practice.

Incidentally, the γ value for setting the color separation curve for each color plate of Experiment A (No. 1 to No. 2), and M ₁
The dot% values (calculated values) at the points are as follows; The γ value of the BL plate is γ = −0.25.

Further, the outline of the basic experiment and the experiment A (N
o. FIG. 4 shows a color separation curve (gradation conversion curve) for each color plate used in 1) and Embodiment B (No. 1). In the figure, (a) is a combination of color separation curves that has been adopted as a standard in this industry for maintaining gray balance. The design materials are given in Table 2. In the figure, (A) is a combination of color separation curves (gradation conversion curves) of each color plate of experiment A (No. 1), and (B) is the color of each color plate of experiment B (No. 1). A combination of decomposition curves (gradation conversion curves) is shown.

<Applied Experiment> In this experiment, a color separation experiment is performed by a method closer to the daily color separation work, and the color tone management method using the <tone conversion formula> of the present invention determines the color tone of the color print image. The purpose is to make sure that they have the ability to reasonably coordinate and manage. In this experiment, the tone intensity value of the C plate image was set to 50% with respect to the color tone management point (M ₁ ).
It became the point that becomes. In addition, the details of the color tone adjustment (specific details of the color tone correction and change requested by the user, etc.) at the color tone management point (M ₁ ) are defined as the halftone dot% of each color of C / M / Y of each color plate image. "DIC GRA" manufactured by Dainippon Ink and Chemicals, Inc. is used as the basic scale specified by the value.
FG Color Chart "(March 1991, second edition)
It was adopted. In this experiment, the halftone dot value of the color chart was read as the gradation intensity value (%) and adopted. In this experiment, six colors were selected from the color chart. In Table 4, the above-mentioned "DIC GRAF-G
6 types of colors selected from the "color chart" and designated gradation intensity values for color tone adjustment are shown.

In the above-mentioned color chart, the above-mentioned 6 kinds of colors have a gradation intensity value of C / M of 12 between 0 and 100.
It is displayed in stages, and Y / BL (having a constant gradation intensity value, for example, a gradation intensity value of 10% or 50% as shown in Table 4) is shown as a color overprinted thereon. Has been done. Therefore, the specified gradation strength value for color tone adjustment can be easily specified in the same chart, and Table 4 shows the specified gradation strength value. Needless to say, it is possible to examine whether the color tone specified by the gradation intensity value described above can be faithfully reproduced on the color plate image without causing deterioration of gradation. , The purpose of this experiment.

[0083]

[Table 4]

Table 5 below shows each color plate design material for this experiment prepared based on the material of Table 4 above. (Note 1) In this experiment, as the gradation intensity value at the point M _1, it goes without saying that the specified gradation intensity value for color tone adjustment in Table 4 was adopted. (Note 2) In the experiment A of this experiment, the gradation intensity value for the M / C plate of the S part was obtained by the following formula (2). For the S part of C plate, the value (9
5%) was adopted. The standard values of (2) below are shown in Table 2.
Is shown in Further, when the calculation result by the following formula (2) exceeds the standard halftone dot% value, the standard halftone dot% value is adopted. S portion of the dot% value = (standard value of the S portion) × (tone intensity value specified in the _{M 1)} / (standard value of _{M 1)} ......... (2) (3) color original image (pot Since the catch light portion is selected as the H portion of), the halftone dot% value of the H portion of all color plate images is “0” (zero). (Note 4) The BL plate (black ink) plate is a skeleton type, that is, the starting point of black ink in accordance with the conventional method.
t, SP) is M ₁ point, and the end point (end point,
EP) was designated as part S. Further, the maximum halftone dot value of the BL plate put in the S part was set to 80% in the experiment A and 70% in the experiment B.

[0085]

[Table 5]

The results of the applied experiments were all as expected, as in the basic experiments. The color tone at the color tone management point (M ₁ ) obtained in the color reproduction image is completely in agreement with the color tone on the color chart as the basic scale, and the gradation is not limited to the entire dynamic range of the H part to the S part. The color tone was also natural to human eyes. That is, based on the results of the above-mentioned applied experiments, the color separation technique using the <tone conversion formula> of the present invention as a tool further integrates the tone adjustment and the tone adjustment when performing the tone adjustment management. Above, it was confirmed to have rationality.

FIG. 5 is a block diagram of an image forming apparatus according to the second embodiment of the present invention. The image forming apparatus of the second embodiment uses the conventional inverse log conversion unit (16) as it is. Therefore, ye ', me', ce ', ke' are output in logarithmic form in the gradation conversion unit (11). As a result, the existing system can be remodeled into the image forming apparatus of the present invention by making changes to the device configuration of the conventional image forming apparatus less than in the first embodiment.

FIG. 6 shows an image forming apparatus according to the third embodiment of the present invention. In the image forming apparatus of the third embodiment, the conventional gradation control (IMC) unit (17) is left as it is, and in addition to the channel connecting the inverse log conversion unit (16) and the gradation control unit (17), the gradation A gradation conversion unit (11) that receives Y, M, C, and K signals is arranged in the front stage of the control unit (17), and the gradation conversion unit (11) is provided with the inverse log conversion unit (16). ) Consists of a side-by-side connection channel. The gradation conversion unit (11) outputs ye ', me', ce ', ke' in logarithmic form as in the second embodiment. The image forming apparatus of the third embodiment is a gradation control unit of a conventional system, that is, a gradation control (IM
Since the C) section (17) is left, it also has a gradation adjusting function which is used in the conventional system. In addition,
The gradation conversion unit (11) according to the present invention is the same as the conventional (IM
Although C) and (17) are made unnecessary, the (IMC) (17) may be left as described above depending on customer needs.

FIG. 7 shows an image forming apparatus according to the fourth embodiment of the present invention. The image forming apparatus according to the fourth embodiment includes a gradation control (IMC) unit (1
7), an inverse log conversion unit (16) and a color channel selector (12) are connected to a channel, and a gradation conversion unit (11) of the present invention is additionally provided. That is, the gradation conversion unit (11) receives Y, M, C, K signals from the preceding stage of the gradation control unit (17),
It is directly connected to the color channel selector (12), and the same processing as in the gradation conversion unit of the first embodiment is performed without restricting ye ', me', ce 'and ke' to the conventional system. In form ye ', me', ce ',
ke ′ can be obtained. Then, as in the third embodiment, the image forming apparatus of the present invention is embodied with a slight improvement over the conventional system.

FIG. 8 shows an image forming apparatus according to the fifth embodiment of the present invention. In the image forming apparatus of the fifth embodiment, the entire conventional gradation conversion unit is newly configured as the gradation conversion unit (11) of the present invention, and in the gradation conversion unit (11), > Is operated to perform gradation conversion and gradation and color tone adjustment management.

In the embodiment of the image forming apparatus shown in FIGS. 3 and 5 to 8, the image forming section is an electrophotographic apparatus in which an electrostatic latent image is formed on a photoconductor having photoconductivity by scanning with a laser beam. It is of the formula. As a means for forming an image by the distribution of pixels, other means such as an electrostatic recording type,
It goes without saying that various types such as a magnetic recording type can be adopted.

FIG. 9 shows a method of forming a duplicate image by the electrostatic recording method. As shown in the drawing, a large number of recording electrodes (f) are formed in the direction perpendicular to the moving direction of the recording head (f), that is, the moving recording body (e) made of a sheet-like dielectric. _In the recording head (f) configured by arranging ₁ ) and the counter electrode (f ₂ ), a voltage is applied to each recording electrode (f ₁ ) to form an electrostatic latent image. The process after the step of adding toner to the latent image and developing is the same as in the case of the electrophotographic system. In the figure, (e ₁ ) of the recording material (e) represents a recording layer (dielectric material), and (e ₂ ) represents a base layer (low resistance material). An output value (voltage value) corresponding to an image to be recorded is applied from the dot control section (14) of the output section (4) to the recording head (f) as an assembly of electrodes.

In the magnetic recording system (not shown), a drum body whose surface is uniformly covered with a magnetic body is used as a recording body, and an image information signal is transmitted to the magnetic recording head in contact with the surface. The magnetic recording head and the recording confronting surface are moved relative to each other while a voltage is applied to form a magnetic latent image on the recording confronting surface. Toner for the magnetic material is used for developing this latent image, but other image duplication processes are the same as those for the electrophotographic method.
As described above, by modifying the gradation adjusting unit of the conventional image forming apparatus according to the present invention, it is possible to combine the operation of the <gradation conversion type> and other image processing, and to optimize the system. In addition to speeding up and downsizing, the cost performance around the system can be improved.

[0094]

According to the image forming apparatus of the present invention, the gradation converting section, which is a core component of the image forming apparatus, uses a specific <gradation converting expression> to generate gradation (tone) and color tone (color tone).
Both can be integrated for color separation. The quantitative and rational integration of the above-mentioned gradation and color tone adjustment was difficult in the prior art and is a breakthrough point of the present invention. In the prior art, when an attempt is made to meet the needs of a specific portion, a specific portion (area) with high market needs (high demand), and further adjustment of the color tone of the entire image (correction and change of color tone), Not only can adjustments not be performed quantitatively, but the color tones of the part concerned and other parts are unbalanced, and the tones (gradation and color tone) of image merging are distorted, producing high quality color reproduction images. The current situation is that it is not possible.

On the other hand, the color separation (gradation conversion) technique incorporated in the heart of the image forming apparatus of the present invention has a specific
By adopting and operating the gradation conversion formula>, gradation adjustment and color tone adjustment can be quantified completely, color document images can be color-separated for the purpose, and gradation reproduction is reproducible. It is possible to efficiently produce a high-quality color reproduction image in which the color tone is adjusted as well as the color tone.

That is, the image forming apparatus of the present invention has the following excellent effects. (1) It is possible to rationally meet the needs for quality of color reproduction images in advanced, complicated and diversified markets. (2) Production of color reproduction images, especially color separation work is quantitatively and reasonably practiced, so productivity is improved, work time is shortened, equipment is efficiently used, consumable materials are saved and reduced. Have a significant effect on. (3) In producing a color reproduction image, it is possible to pave the way for rationally utilizing the sensitivity and artistry of an industrial production system. As a result, high added value of the image forming apparatus is realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a density characteristic curve of a color film (manufactured by Company F).

FIG. 2 is a diagram illustrating a gradation expression method.

FIG. 3 is a block diagram of an image forming apparatus according to a first embodiment of the present invention.

FIG. 4 is a diagram illustrating an outline of a basic experiment of the present invention and a color separation curve (gradation conversion curve).

FIG. 5 is a block diagram of an image forming apparatus according to a second embodiment of the present invention.

FIG. 6 is a block diagram of an image forming apparatus according to a third embodiment of the present invention.

FIG. 7 is a block diagram of an image forming apparatus according to a fourth embodiment of the present invention.

FIG. 8 is a block diagram of an image forming apparatus according to a fifth embodiment of the present invention.

FIG. 9 is an explanatory diagram of an image forming unit using an electrostatic recording method.

[Explanation of Codes] 1 ...... Detection unit 2 ...... Color separation unit 3 ...... Grayscale adjustment unit 4 ………… Grayscale conversion unit 5 ………… Color original image

Claims (11)

[Claims] 1. A gradation conversion unit of an image forming apparatus performs gradation conversion on image information of a continuous gradation color original image to produce a halftone (halftone) color reproduction image on a desired image expression medium. In the image forming apparatus, the gradation conversion unit includes (1) a characteristic curve of a recording medium on which a color original image is recorded [a light amount value (x value) incident on the recording medium and a density formed on the recording medium. A characteristic curve that defines the relationship with the value (D value) in the Dx orthogonal coordinate system] is used to obtain the light amount value (x value) from the density value (D value). (2) The light amount value ( x value) is gradation-converted using the following <gradation conversion formula> to obtain a gradation intensity value (y _n value),
And (3) a color tone adjustment function used at the time of gradation conversion, wherein the color tone adjustment function is (3) -1. H part (lightest part) to S part (darkest part) of the color original image. A color tone management point (M ₁ ) for managing the color tone of the color reproduction image is set in a predetermined part between the two, and (3) -2. At the color tone management point (M ₁ ), the color tone adjustment condition is Desired color plate (C plate, M plate, Y plate, and B plate)
(L plate) gradation intensity value, and (3) -3. The gradation intensity value of the color plate reflecting the light intensity value at the color tone management point (M ₁ ) and the adjustment condition of the color tone, and the H part. The desired gradation intensity value set in the S section is substituted into the following <Gradation conversion formula> to determine the γ value, and the light intensity values of the pixels from the H section to the S section of the color plate are calculated as the gradation intensity value ( <Gradation conversion formula> for gradation conversion into y _n value), and (3) -4. <Gradation conversion formula> for each color plate whose γ value is determined.
And an image forming apparatus having a color tone adjusting function configured to convert the light amount value of each pixel for each color plate by gradation and manage and adjust the color tone. <Gradation conversion formula> y _n = y _H + [α (1-10 ^−kx ) (y _S −y _H ) / (α−β)] In the above <Gradation conversion formula>, the meaning of each symbol is as follows. is as follows; x: shows the (x _n -x _H). That is, a color original obtained in the same manner from the light quantity value (x _n ) corresponding to the density value (D _n ) of an arbitrary pixel point (n point) of the color original image obtained using the characteristic curve of the recording medium. The basic light amount value obtained by subtracting the light amount value (x _H ) corresponding to the density value (D _H ) of the H portion of the image is shown. y _n : Gradation intensity value set for a pixel on the color reproduction image corresponding to an arbitrary pixel point (n point) on the color original image. y _H : Gradation intensity value preset in the H portion on the color reproduction image corresponding to the H portion on the color original image. y _S : A gradation intensity value preset in the S portion of the color reproduction image corresponding to the S portion of the color original image. α: Surface reflectance of an image representation medium for recording a color reproduction image. β: Numerical value determined by β = 10 ^−γ . k: Numerical value determined by k = γ / (x _S −x _H ). However, x _S represents a light amount value (x _S ) corresponding to the density value (D _S ) of the S portion of the color original image obtained by using the characteristic curve of the recording medium. γ: arbitrary coefficient. 2. The image forming apparatus according to claim 1, wherein the color original image is recorded on a photoelectric conversion element as a recording medium. 3. The characteristic curve of the recording medium is a photoelectric conversion characteristic curve that defines the relationship between the light amount value (x value) incident on the recording medium (photoelectric conversion element) and the formed density value (D value). Item 2. The image forming apparatus according to item 2. 4. The image forming apparatus according to claim 1, wherein the color original image is recorded on a photographic light-sensitive material as a recording medium. 5. A characteristic curve of a recording medium is a photographic density characteristic curve that defines a relationship between a light amount value (x value) incident on a recording medium (photographic photosensitive material) and a formed density value (D value). Item 4. The image forming apparatus according to item 4. 6. The image forming apparatus according to claim 1, wherein the color original image is a color print (reflection type) original image. 7. The characteristic curve of a color print (reflective type) original image is defined by a relationship between a light quantity value (x value) and a density value (D value) of 1: 1. Image forming apparatus. 8. A method of producing a color reproduction image on an image representation medium is a method of producing a laser beam on an image forming body having a uniformly charged photoconductive layer for recording pixels on a recording sheet. The image forming apparatus according to claim 1, wherein a latent image representing the distribution of the pixels is formed by scanning, the latent image is developed by toner, then transferred to a recording sheet, and further fixed. 9. A series of operations of forming a latent image on an image forming body, developing with toner, transferring to a recording sheet or a part thereof is performed by using toner of a specific color, and the same operation is performed with different colors. 9. The image forming method according to claim 8, wherein a color image is formed by performing the operation with toner, repeating the same operation for a required number of colors, aligning and transferring it on the same recording sheet, and then fixing. apparatus. 10. A method of producing a color reproduction image on an image representation medium, comprising a method in which a plurality of electrostatic recording bodies moving for recording pixels on a recording sheet are arranged in a direction perpendicular to the moving direction. 2. A voltage is applied to the recording electrode of to form an electrostatic latent image on an electrostatic recording body, the latent image is developed with toner, then transferred to a recording sheet, and further fixed. The image forming apparatus described. 11. A series of operations of forming a latent image on an electrostatic recording body, a phenomenon with a toner, a transfer to a recording sheet or a part thereof is performed by using a toner of a specific color, and the same operation is performed with different colors. 11. A color image is formed by carrying out the same toner as described above, repeating the same operation for a required number of colors, aligning and transferring it on the same recording sheet, and then fixing it. The image forming apparatus described.