JPH0440165A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain a copied picture arbitrarily correcting or changing a picture characteristic by outputting a picture information value by utilizing the photoelectric conversion characteristic curve of a sensor, and converting the value to a gradation strength value for gradation adjustment according to a gradation conversion formula. CONSTITUTION:By using an adjusting part 11 instead of a gradation control part and an inverse log conversion part, T, M C and K components converted to the picture information values in correlation to the quantity of light are converted from T, M, C and K to ye', me', ce' and ke' in this part 11. The adjusting part 11 has the algorithm of the gradation conversion formula in the inside and applies the gradation conversion formula for the respective Y, M, C and K so as to calculate the ye', me', ce' and ke'. The area ratio (gradation strength value) obtained by the control part 11 is inputted to a color channel selector 12, and the color channel selector 12 successively and selectively outputs the ye', me', ce' and ke'. This output is inputted to an output part 4 after A/D conversion in an A/D conversion part 13. In the output part 4, a laser beam is controlled by a dot control part 14 based on the output of a gradation control part 3.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention converts image information signals obtained from original images using a new gradation conversion method, thereby achieving excellent gradation reproducibility. The present invention relates to an image forming apparatus capable of forming duplicate images.

Specifically, the present invention provides various original images C.
The meaning of the original image should be interpreted in the broadest sense, and includes everything that is to be reproduced using various image expression media such as recording paper, CRT, and liquid crystal. Therefore, copying,
It must be kept in mind that the concept of a manuscript is broader than the concept commonly used in copying, and it also covers subjects such as still life and people, as well as photographic objects. Obtain the true image information value, convert it using a gradation adjustment mechanism using a specific gradation conversion formula, and express the image on recording paper etc. based on the gradation-converted output signal. An image forming device that can form a reproduced image with excellent gradation and color reproducibility on a medium (in the present invention, the meaning of “image forming device” should be interpreted in the broadest sense, and includes copying equipment, printer equipment, etc.) , prepress equipment 1, image transmission equipment, TV image carrier equipment, electronic camera equipment, etc., all of which have the function of forming duplicate images are subject to this invention.

More specifically, the present invention provides an image information input sensor (
As is well known, this is composed of photoelectric conversion elements such as photomultipliers, CCDs, two-dimensional CCDs, and photodiodes. ), but in the present invention, as in the past, image information values correlated to the density after being processed by the sensor system (as described later, this term is It should be interpreted in the broadest sense, and may also be referred to simply as a density information value. The present invention relates to a completely new image forming apparatus that has a gradation adjustment mechanism that converts image information values based on a specific gradation conversion formula.

(Prior art) When copying an image from a continuous tone original image such as a photograph onto a recording sheet using an image forming device such as a copying machine, analog processing of the original is required when photosensitive paper is used as the recording sheet. By (exposure), an image having continuous gradations corresponding to the original image is formed (silver halide photographic recording). On the other hand, various printers, copying machines, etc. that digitally record images on photosensitive paper or plain paper.

Since images are not formed using the analog processing described above, it is difficult to reproduce density gradations.
Particularly in the case of duplicating a color image, it is not easy to adjust the tone (color balance) as well as the density gradation described above.

For this reason, efforts are being made to improve the reproducibility of gradations and color tones in various image forming apparatuses.The formation of duplicate images in image forming apparatuses has changed from the continuous gradation of photolithography in printing to halftone dots. Similar to the method of converting to gradation, density information values obtained by photoelectric scanning of an original image with continuous gradation, such as a photograph, are processed, and the gradation and color tones corresponding to the original image are converted using the signal. The idea is to form an image consisting of a distribution of pixels on an image representation medium.

However, current image forming apparatuses use unscientific gradation adjustment methods that process density information values obtained from original images to reproduce density gradations.
At present, it is not possible to obtain satisfactory density gradation and the reproducibility of color tone closely related thereto.

As is well known, the density gradation of a duplicate image depends on the pixel density display method. A method for displaying such pixel density gradations is a method that changes the pixel coverage rate depending on the size of the dot (size modulation method, variable area dot method. This method is used in monochrome and color scanners for producing printed images. , piezoelectric inkjet, etc.), a method of changing the pixel coverage by a specified number of dots (of the same size) (density modulation method, constant dot; this method is seen in thermal melt transfer, etc.), and a method of changing the density of the prescribed (same size) dot itself (11 degree modulation method, variable density dot. This method is seen in thermal dye sublimation transfer. Also, CRT, crystal, etc. that form an image by adjusting the brightness of pixels Also included in this category are TV picture tubes constructed from the above.

).

However, as described above, when attempting to reproduce a document image using various conventional image forming apparatuses, for example, a duplicate image corresponding to the density information value of a predetermined sample point (pixel) on the document image is In the upper pixel, the dot diameter and density determine the pixel coverage rate (the ratio of recording to the number of unit pixels that make up a pixel block), that is, the density gradation of the pixel. (hereinafter referred to as the gradation intensity value or simply the gradation intensity value of a pixel).

This term is commonly used in the various pixel density gradation display methods described above. ), and how to obtain the gradation intensity value of such a pixel has not been scientifically studied.

That is, for the density information value of a predetermined pixel on the original image,
Regarding what kind of pixel gradation intensity value should be correlated with the pixel on the duplicate image corresponding to the pixel,
No scientific correlation formula has been developed, and currently these equipment manufacturers have no choice but to rely on correlation formulas determined in advance based on experience, intuition, or a limited number of fixed conditions.

As a result, it is possible to produce original images with a quality that was not expected by the equipment manufacturer, such as non-standard (overexposed and bright originals).
In the case of color film originals (such as underexposed and dark originals, high-key or low-key originals, or originals with color fog or fading), it is extremely difficult to obtain a desired reproduced image with excellent gradation and color tone. Therefore, it is possible to obtain duplicate images of the desired quality not only from original images with standard image quality but also from non-standard original images mentioned above, and to arbitrarily change or modify the image quality of the original image (gradation level). or color tone changes or corrections)
It has not been possible to develop an image forming apparatus with the flexibility to perform

This is how conventional image forming apparatuses convert the density information value of a predetermined pixel on a document image, which is an extremely important image information value when producing a duplicate image, into the gradation intensity value of the corresponding pixel on the duplicate image. This means that it is not possible to convert it scientifically and rationally.

(Problems to be Solved by the Invention) The cause of the above-mentioned problems in conventional image forming apparatuses is that when forming a duplicate image based on the final pixel distribution from an original image such as a continuous tone image, It is recognized that this is due to the concept of the image density gradation conversion process, which is the first stage and plays an important role.

In other words, when converting the density information value of a predetermined pixel on the original image into the gradation intensity value of the corresponding pixel on the duplicate image, the conventional image gradation conversion technology has become a scientifically rational conversion technology. It can be recognized that this was not based on anything but relied solely on experience and intuition.

Under these circumstances, the present inventors believe that in order to ultimately streamline the image forming process and produce reproduction images of excellent quality, it is necessary to establish a rational image gradation conversion technology. We conducted extensive research based on the basic understanding that

As a result, the original image is input as the image information value to be used when converting the density gradation in various original images to be copied by the image forming apparatus, and the image information value for forming the duplicate image is input. The density information value of the original image obtained from the mechanism that detects (reads) the image information (hereinafter referred to as the image information input sensor section or simply called the image information input sensor) (this may be a physical quantity correlated to the density as described later). However, instead of using the density information value of the original image (detected by the sensor unit) of each image information input sensor, A characteristic curve that defines the relationship between the image information value correlated to the light amount of the original image input to the image information input sensor (hereinafter, in the present invention, the image information input sensor system is composed of some kind of photoelectric conversion element). Therefore, the above-mentioned characteristic curves of each image information input sensor system are collectively referred to as photoelectric conversion characteristic curves. When converting image information values using a specific gradation conversion formula to obtain gradation intensity values for gradation modification, it is important to not only maintain image characteristics that are faithful to the original image, but also to arbitrarily modify or change the image characteristics. It has been found that duplicate images can be obtained.

As described above, the present invention improves the reproduction image production technology that emphasizes the density information value of the original image detected by the image information input sensor of the conventional image forming apparatus, and improves the original image that should be the true target of reproduction. This is a completely new reproduction image production technology that emphasizes the image information value that the document image has, that is, the image information value that correlates with the amount of light that enters the image information input sensor system of each image forming device from the original image. The present invention aims to provide an image forming apparatus incorporating tone conversion technology.

[Structure 1 of the Invention (Means for Solving the Problems) To summarize the present invention, the present invention provides an image forming apparatus for forming a duplicate image from an original image. The sensor unit is connected to a photoelectric sensor of the sensor that defines the relationship between an image information value (Xn) correlated to the amount of light input from the original image to the sensor and an image information value (Dn) correlated to the density output from the sensor. The conversion characteristic curve is used to output an image information value (Xn) correlated to the amount of light input from the original image to the sensor; The image information value (x
7) into a gradation intensity value (y value) for gradation adjustment using the following gradation conversion formula (1)〉. The present invention relates to an image forming apparatus for forming reproduced images with excellent quality.

Gradation conversion formula (1) Hereinafter, the configuration of the present invention will be explained in detail.

First, the theoretical background of the image gradation conversion method employed in the image forming apparatus of the present invention will be mentioned to clarify the positioning of the present invention.

The theory of image gradation conversion of the present invention was developed to solve the problems of gradation conversion during the production of printed images, which is a particularly typical field of technology for producing duplicate images. , much of which will be explained in relation to techniques for producing printed images by means of scanners (monochrome and color scanners). However, this is for the convenience of explanation, as there are similar problems with gradation conversion in various image forming devices such as printers, copiers, and DTP (desktop publishing) related equipment. When the value of the tone conversion theory of the present invention is built into these image forming apparatuses, its value is not diminished in the slightest.

The present inventors have provided rational theoretical support for image gradation conversion technology, and have achieved reproducibility of tone (including both density gradation and color tone) even from the various original images described above. In order to go even further and rationally produce a duplicate image with a desired tone, two core elemental technologies are needed in the production of duplicate images: gradation conversion technology fgradat.
ion control and color correction (correction) technology fc
color correction) - color correction (
(Correction) Prior to improving technology, we believe that technology that can rationally convert the density gradation of each pixel of an image must be given primary importance.

The points mentioned above are related to color correction (correction), which is relatively easy to scientifically analyze (analysis using masking equations or Neugebauer equations) in the production of reproduced images, as typically seen in the production of color printed images. This is a great opportunity to reflect on the conventional technology, which places more emphasis on color matching technology than image density gradation conversion technology.

The present inventors have also discovered that the current image density gradation conversion technology used when creating a duplicate image from an original image is applicable to a color film original when creating an original image, for example, a printed image that is a duplicate image. (original image), the density characteristics from the brightest part to the darkest part are not reasonably understood, and the density characteristics that are essential for converting the density characteristics of the original image into a reproduced image with 1:1 fidelity. There is a basic understanding that the determination of the correlation (gradation conversion formula) between both images (original image and duplicate image) has no rational theoretical support and remains solely dependent on human experience and intuition.

Based on this basic recognition, the present inventors previously proposed a specific gradation conversion formula in order to make the image gradation conversion technology scientific and rational (Unexamined Japanese Patent Publication No. Showa 64-7770
Publication, Japanese Patent Application No. 63114599, Japanese Patent Application No. 1983-20
7326, U.S. Patent No. 4.811.108)
.

However, in subsequent research by the present inventors, it was discovered that there are certain limitations to the image gradation conversion technique performed under the above-mentioned specific gradation conversion formula.

This limitation is that, as mentioned above, the true target of a duplicate image is the original image, and when duplicating, the true image information value of the original image should be used.
In conventional image gradation conversion techniques, including the previous proposal by the present inventors, image information values detected by the image information input sensor of an image forming apparatus, especially the density related to the density and brightness of the original image, are used. This means that image gradation conversion is performed using information values as clues. This depends on the photoelectric conversion characteristics of the image information input sensor system, and does not mean that the image information of the original image itself is used.

This will be explained by taking as an example the case where a color print image is produced as the above-mentioned duplicate image.

As is well known, when producing a color print image, a color film original (in the present invention, in order to distinguish it from the above-mentioned original image, (This is also called a media image) is the starting point for the work. Then, the color film original (media image) is sent to a color scanner (color separation device).
Using this, the image information input sensor system of the scanner separates each color and detects the image information value, and this is used to produce a color print image.

According to the definition of the present invention, (i) from the perspective of the image information input sensor system of a color scanner, a color film original is referred to as an original image. (ii) If a subject such as a still life or a person is viewed as a document image, a color film document can be viewed as a medium image for detecting image information of the document image. In other words, the color film original can be said to have the function of an image information input sensor for detecting image information correlated to density.

In the present invention, from the viewpoint of accurately reproducing the gradation of an original image (the above-mentioned subject such as a still life or a person), the following description will be made assuming that the character of a color film original has the above-mentioned (11).

In addition, in the present invention, even if the character of the color film original is interpreted as the above (it), it goes without saying that a color printed image with superior gradation reproducibility compared to the conventional one can be obtained. There is no such thing.

As mentioned above, in the production of color printed images, conventionally, the light incident from the subject (original image) to the photographic light-sensitive material (photosensitive emulsion layer), which is the recording medium, is controlled under predetermined exposure conditions (as is well known). , when the intensity of the incident light is I and the incident time is t, the exposure amount E is expressed as E=It. , which includes both the color correction and gradation control described above.

The photographic light-sensitive material on which the subject (original image) has been photographed has a photographic density (photogra-phic) by development.
The curve representing the correlation between the photographic density (degree of blackening) and the exposure amount E of the photographic light-sensitive material is the photographic density characteristic 11iI. (photogra
phic characteristic curve
It is l. This represents the photographic density (il (D =
LogIO/I), and the horizontal axis shows the logarithm of the exposure amount E (logE
) is displayed. In addition, for film and dry 11ii (transparent originals), the ratio of the intensity of transmitted light I to the intensity of incident light Io, and for photographic paper (reflective originals), the ratio of the intensity of reflected light ■ and the intensity of completely reflected light It goes without saying that the ratio with IO is used.

A typical photographic density characteristic curve is a fairly complex curve that has a downwardly convex foot, a substantially straight line, and an upwardly convex shoulder (this point can be explained in Figure 1 below). It is well known that

In other words, the color separation technology used to produce conventional color printed images is a color separation technology assembled from the standpoint of the vertical axis (density value) of the photographic density characteristic curve, and The amount of exposure incident on a photographic light-sensitive material (hereinafter, in the present invention, since the absolute value of the amount of exposure or the relative value may be used as described later, "image information value correlated with the amount of light") ), that is, the horizontal axis of the photographic density characteristic curve (not a color separation technology constructed from the standpoint of image information (1) correlated to the amount of light), and the color separation technology based on color film originals, which is the basis of color separation work in the prior art. As is clear from the shape of the photographic density characteristic curve, the density information value is different from the image information value that correlates with the light amount of the object (original image); in other words, the image information of the object is not linearly provided.) However, due to changes in conditions such as exposure conditions and development conditions, the appearance of the 3' IEMs of both types will vary widely.

In other words, since it is affected by the photosensitive characteristics of the photographic photosensitive backing material that is the recording medium, the photographic density, which is the density information value of the color film original that is the medium image, and the image information value that correlates with the light amount of the subject (original image) is a linear relationship (1: 45° of l
(linear relationship).

On the other hand, it is well known that human vision has a logarithmic discrimination characteristic for brightness and darkness, and one person can see the subject (
The brightness and darkness of the amount of light incident on the visual system (original image) is evaluated based on the above-mentioned discrimination characteristics. Here, we perceive a linear gradient of concentration change as natural.

Therefore, in the production of color printed images, if we proceed with the work based on the density value (D=log''/I) of the color film original (medium image) recorded on the photographic light-sensitive material, it is the density value of the color film original (media image) recorded on the photographic light-sensitive material. This means that the density information value after being influenced by the photosensitive characteristics is used, and it does not mean that the image information value that correlates with the light amount of the object (original image) that is the true object of duplication is used.

In view of the above-mentioned situation, the present inventors have developed a method for producing a duplicate image by using a recording medium (such as a photographic light-sensitive material) or a photomultiply, a photosensitive material constituting an image information input sensor system of an image forming apparatus. The original image (substantive image) that is the true target of reproduction without using the density information value of the original image that is affected by the photosensitive characteristics and photoelectric conversion characteristics of photoelectric conversion elements such as diodes, CCDs, and two-dimensional CCDs.
We conducted extensive research on methods for producing various types of replicated images based on image information values that correlate with the primary (raw, primitive) amount of light.

As a result, in the production of color printed images, the vertical axis (D=log 10/
The value of the horizontal axis (1, gE) is calculated from the value of 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). The density information value (D
value) on the X axis to obtain the image information value (X value) on the X axis.
(2) More specifically, the density value (Dn value) of any pixel on the medium image on the D axis is projected onto the X axis via the photographic density characteristic curve to obtain the image of the corresponding pixel. Information value (Xn value) (X
In the photographic density characteristic curve, the axis indicates the logarithmic value of the exposure amount, but in the present invention, the absolute value or D
It is equally effective to use a relative value read with the same scaling as the axis, so as mentioned above, this can be used as an image information value correlated to the amount of light incident on the recording medium from the subject.
, or simply "image information value correlated with the amount of light."

), and then (3) Based on the value x obtained as above,
In addition, by applying the specific gradation conversion formula previously proposed by Hondaimei et al., the gradation intensity value indicating the halftone area % value was obtained from the skin value, and the size of the halftone dot was controlled by this. It has been discovered that when the image is processed, a printed image with excellent halftone gradation and image characteristics faithful to the subject (original image) can be obtained.

The image gradation conversion method employed in the image forming apparatus of the present invention has been explained using the production of color printed images as an example.
This is similarly effective in forming other duplicate images. In particular, the present invention converts the density information value of an arbitrary pixel on an original image into a gradation intensity value of a corresponding pixel in a duplicate image, as described above (on various recording media (photographs)). The density information value of the original image obtained through the image information input sensor of the image forming apparatus is not used as is. These various recording media The image information value (correlated with the amount of light incident on the image information input sensor system) is obtained, and this is processed using the above-mentioned gradation conversion formula (1) to convert it into a gradation intensity value. It has a major feature in the way it is carried out.

Next, the derivation method and characteristics of the gradation conversion formula (1) of the present invention will be explained.

In a duplicate image formed by an image forming device, the basic components that make up the duplicate image are the gradation intensity value at a predetermined pixel and the image forming material (ink, toner, etc.)
The surface reflection density (brightness value for TV images, etc.) and the ability of human vision to easily identify, for example, a 1% difference in the size of halftone dots in a printed image as a density difference. As can be seen from the fact that 0 is set for a certain predetermined pixel, the gradation intensity value of the pixel, which has the same relationship as the size of the halftone dot area, plays an extremely important role as an image forming means. Focusing on dots, we investigated the effects of changes in the amount of ink applied on the dots and changes in the size of the dots on the density gradation, and found that the latter was much larger, and the reproducibility of the gradation was significantly lower. How to set tone intensity values is an extremely important issue in producing reproduced images with excellent quality. Reproduced images with excellent density gradation reproducibility also have excellent color tone reproducibility.
This can be confirmed in many cases.

In addition, in connection with the above, when attempting to produce a duplicate image using an image forming device, the quality of the original image varies widely, and the image forming process also has various characteristics. Furthermore, there is a background that image quality evaluation standards are not uniform, and it is strongly desired that a mechanism to overcome these complex and unstable factors be built into the image forming device. .

For this reason, when producing a duplicate image with halftones using an image forming apparatus from an original image such as a continuous tone image, the gradation intensity value (yh) of the pixel in the brightest part (H) on the duplicate image is and the gradation intensity value (y, ) of the pixel in the darkest part (S)
It is absolutely necessary to provide a method that allows the user to arbitrarily select and manage the density gradation of an image from the brightest part (H) to the darkest part (S) in a rational and simple manner. It is.

Based on this idea, the gradation adjustment method of the present invention was devised, specifically, the gradation adjustment method using the above-mentioned <gradation conversion formula (1)>.

The present inventors have discovered that when producing a halftone printed image from a continuous tone color film original, the tone conversion (
A gradation conversion formula similar to the gradation conversion formula (1) of the present invention, which is used to convert continuous gradation to halftone gradation), was previously proposed (in Japanese Patent Application Laid-open No. 64-7770 and Japanese Patent Application No. 63-114599), the operating conditions thereof are completely different from those of the present invention.

<Gradation conversion formula> to calculate the number M (y) of the halftone area percentage used when producing a printed image with the halftone gradation proposed above (As mentioned above, the basic framework is Although it is similar to the gradation conversion formula (1) of the invention, all of its operating conditions (which are different) can be derived from generally accepted density formulas (photographic density, optical density). That is, it can be derived by applying D=10g1o/I=log'/T.

When this general formula regarding density is applied to plate making and printing, it becomes as follows.

Ru.

<Tone conversion formula (2)> In this density formula (D') related to platemaking and printing, it is possible to arbitrarily set halftone dots of desired size in the H and 3 parts of the printed image, and , the basic density value (x) at an arbitrary sample point on the continuous tone image (original image) and the halftone area percentage of the halftone dot at the sample point on the corresponding halftone image (printed image). Incorporating the requirement to rationally relate the numerical value (y) and guiding the theoretical value and the measured value to closely match, the result obtained is the following formula (gradation conversion formula (2)). ), and when applying the above gradation conversion formula (2)) to the gradation conversion of an image when producing a printed image, α
.

y□13'! 1 While arbitrarily selecting the γ value, calculate the value of the halftone dot area percentage (y
). This not only makes it possible to faithfully reproduce the density gradation of the original image (continuous gradation image) on the printed image (halftone gradation image), but also achieves the desired image quality (desired density gradation). It is possible to produce printed images with various colors and tones).

In addition, multicolor plate making (generally cyan (C), magenta (M),
It is thought that one set consists of four versions: yellow (Y) and black (BL). ), the working standard characteristic curve of the standard plate (in the case of multicolor plate making, the cyan plate (C) is the standard plate as is well known), that is, the density information value of the original image, is used as the halftone dot of the printed image. The halftone gradation characteristic curve (a curve obtained by graphing the y value and y value described above, which serves as the standard for converting continuous gradation to halftone gradation) Once the halftone characteristic curves for other color plates are determined, the y value of the standard plate is multiplied by the appropriate adjustment value based on the gray balance ratio of each printing ink color. By doing so, it can always be determined rationally.The halftone gradation characteristic curves of each color plate determined in this way are not only reasonable characteristic curves, but also The gradation and tonal interrelationships between the curves are also reasonable and appropriate.

That is, when creating a halftone print image from a continuous tone original image, the tone conversion of the image is performed using the above-mentioned tone conversion formula (2).
)>, it is possible to break away from the conventional image gradation conversion method that relies on experience and intuition, and perform image gradation conversion arbitrarily and rationally. Color tones that are inseparable can also be rationally adjusted. As a result, it is possible to obtain a printed image having a density gradient and color tone that are natural to the human visual sense.

The above explanation has centered on the case of producing a printed image with halftone gradation as a reproduced image, but there are various theories that support the gradation conversion work using the above-mentioned gradation conversion formula (2)〉. Needless to say, the present invention can also be applied to the production of duplicate images using image forming apparatuses such as printers and copying machines.

However, when producing a duplicate image using the above-mentioned gradation conversion formula (2), density information values are used for density gradation conversion.

On the other hand, in the image gradation conversion of the present invention, in order to achieve better density gradation conversion as described above,
As the image information value of the original image to be adopted during gradation conversion,
Instead of using conventional density information values, image information values that are correlated to the amount of light are used. In order to perform the gradation conversion of the present invention, which is different from the conventional method described above, the gradation conversion formula (2
)>, it goes without saying that the operating conditions for gradation conversion formula (1) can be summarized as follows.

Next, the meaning of each term of the <gradation conversion formula (1)> of the present invention, the operational characteristics, etc. will be explained.

In the operation of the <gradation conversion formula (1)> of the present invention, the basic light amount value (x) of each pixel on the original image must be determined. As described above, the basic light amount value (x) is the density information value (Dn value) of a predetermined pixel on a document image obtained by the image information input sensor of each image forming apparatus, specifically, a predetermined photoelectric conversion element. Using this as a clue, the photoelectric conversion characteristic curve of the photoelectric conversion element, that is, the image information value (Xn) correlated to the amount of light input from the original image to the sensor system, and the image information correlated to the density output from the sensor Value (Dn
) may be determined from the characteristic curve that defines the relationship between As mentioned above, when producing a color printed image, the characteristics of the color film original (media image) must be determined. ! As mentioned above, the (photographic density characteristic curve) may be used.

In the present invention, the density information value may be any value as long as it reflects the physical quantity related to the density of each pixel of the original image, and should be interpreted in the broadest sense. Synonyms include reflection density, transmission density, brightness, current/voltage value, etc. These density information values may be extracted as density information signals by photoelectrically scanning the original image. In addition, in the above <gradation conversion formula (1)> of the present invention, the basic light amount value (x) is determined from the image information value correlated to the light amount on the horizontal axis scaled by the same scaling as the vertical axis of the density characteristic curve,
(For example, some portraits on positive color film have a density value of 0.2 to 2.70 on the vertical axis, and the corresponding value on the horizontal axis is adopted.)
n [gradation intensity value set for the brightest (H) pixel] and y
s [gradation intensity value set for the pixel in the darkest part (S)]
If you use a percentage value (for example, 5% or 95% pixel coverage), the γ value [gradation intensity value set for a pixel on the duplicate image that corresponds to an arbitrary pixel on the original image]
is calculated as a percentage.

In the operation of the above <gradation conversion formula (l)> of the present invention,
You are free to use it by transforming it in the following ways, as well as by processing it, transforming it, guiding it, etc.

X y"yH+E (1-10Hys -yH) In the above modification, a=1.

This is based on the assumption that the surface reflectance of the recording paper (substrate) on which the duplicate image is recorded is 100%. In practice, the value of α may be lO if the zero point adjustment of the density measuring mechanism is performed using the recording paper as a reference. Further, in the case of a luminance image such as a TV image, α may be set to 1.

Further, according to the modified example (α=1.0), y
3 can be set as planned. This is clear from the fact that in the brightest part H on the duplicated image, X=O, and in the darkest part S, x=[χIn XHn], that is, -kX=-γ. be.

In the operation of the above gradation conversion formula (1) of the present invention,
The numerical values of α, β, and γ (the β value is defined by B=IO−7 as described above) take various values. In the present invention, by appropriately selecting these numerical values, the original Image gradation conversion processing can be performed rationally regardless of the quality characteristics of the image.

That is, the image gradation conversion processing method based on the above-mentioned gradation conversion formula (l) of the present invention reproduces the density gradation and color tone of the original image, that is, it reproduces the tone of the original image into a duplicate image. :1, but its usefulness is not limited to this. In addition to faithfully reproducing the characteristics of the original image, the gradation conversion formula (l) of the present invention has the following advantages: α, β, By appropriately selecting the γ value and furthermore the 3'H+y3 value, it is extremely useful for rationally changing or correcting the characteristics of the original image. Of the parameters in gradation conversion formula (1), the γ value in particular plays a major role in adjusting (including correction or change) the characteristics of the original image. 1)
It is easy to understand if you try to use it.

When forming a multicolor image using the above-mentioned gradation, conversion formula (1), for example, when producing a duplicate image using a color film original, color separation techniques well known in fields such as printing are used, namely: Reduces reflected light from color originals with blue (
B), green (G), and red (R) to obtain a signal correlated to the density information value (D value) for each color, and convert this into an image information value (X value) correlated to the amount of light. , further processed by a gradation adjustment mechanism using the above-mentioned gradation conversion formula (1), and based on this processing information value (y value), the recording unit of the image forming apparatus is adjusted to form an image. good. At that time, calculate the y value for the standard color plate (for example, 0 plate), that is, the gradation characteristic curve (y value) of the standard color plate, and calculate the y value for the X value.
By plotting the values, a gradation characteristic curve similar to the halftone gradation characteristic curve in the printing technique described above is obtained. ), and the gradation characteristic curves for other color versions (M version, Y version) are determined by multiplying the y value of the reference color version by the appropriate adjustment value (based on the gray balance ratio of each ink). Since these can be determined rationally, images can be formed using these gradation characteristic curves.

The gradation characteristic curve for each color plate set as described above is defined by the gradation conversion formula (1), so it is of course a reasonable characteristic curve, and the gradation between those characteristic curves is The interrelationships regarding tone and color tone are also reasonable and appropriate.

Next, a method for obtaining image information (1 (X value)) correlated to the amount of light of the corresponding pixel incident on each recording medium from the density information value (D value) of an arbitrary pixel on the original image will be described.

In the present invention, first, an image information value correlated to density for gradation conversion is obtained from an original image from an image information input sensor of each image forming apparatus, basically a photoelectric conversion element such as a photodiode or CCD. Next, the density information value (
D value) of each photoelectric conversion element (defines the relationship between the density information value of the original image obtained from the photoelectric conversion element and the image information value correlated with the amount of light of the original image incident on the photoelectric conversion element) The image information value (X value) correlated to the light amount of the corresponding pixel may be determined via the characteristic curve (characteristic curve). For this purpose, the characteristic curve of the photoelectric conversion element constituting the image information human power sensor of each image forming apparatus must be accurately or approximately converted into a function (mathematical expression). Note that when using a color film original (medium image) and trying to produce a color printed image that is faithful to the subject that is the source of the color film original, as described above, the recording medium color film (photosensitive material ) may be used to obtain the image information value (X value) correlated to the amount of light.

Here, a case in which a color print image is produced using the above-mentioned color film original (medium image) will be explained as an example. for that.

A method of formulating a photographic density characteristic curve of a photographic light-sensitive material, which is a recording medium for an original image (subject), will be explained. In the present invention, when the image information input sensor of the image forming apparatus is composed of various photoelectric conversion elements, the photoelectric conversion characteristic curves of these photoelectric conversion elements may be expressed in a similar manner.

As a photographic density characteristic curve, a color film (Fujichrome, manufactured by Fuji Photo Film Co., Ltd.) shown in FIG. 1 was used. In addition, in the following mathematical formula, it is assumed that the gradation characteristic curve for the C plate, which is the standard among multicolor plate making, is set. , IQ (photographic density characteristic curve) are shown. Therefore, for other color versions (M version, Y version), G
It goes without saying that the sensitivity characteristic curves (photographic density characteristic curves) of the , B emulsion layers can also be utilized.

The photographic density characteristic curve may be expressed mathematically by any appropriate method, and is not subject to any restrictions.

For example, vertical axis=p=l□glo/I, horizontal axis=X(
However, the scale of the X axis was made to match the D axis. ), and if a + b, c, d + e, and f are constants, then (a) The leg part of the photographic density characteristic curve (the region with a downwardly convex shape and a small D value) D: a, bC・(X+d L”e+f (b) Approximately linear part (area where the D value is an intermediate value in an approximately straight line) D-a-X+b or D=a-x2+bx+c (c) Shoulder part (upwards convex shape) (where the D value is large) D = a ・log (b + (X+c) )
It can be expressed mathematically using +d etc.

Table 1 shows a mathematical expression of the photographic density characteristic curve shown in FIG. In Table 1, in order to mathematically express the photographic density characteristic curve as accurately as possible, there are a plurality of mathematical expression categories.

(Leaving space below) Table 1> Functional formula of photographic density characteristic curve - list of crystals
11 Characteristics In the present invention, as shown in FIG. 1, there is a D-axis scale indicating the density value of a color film original (medium image), and a density value incident on the color film (recording medium) from the original image (subject). The correlation between D and X was expressed as a function on the assumption that the scale of the X axis indicating the image information value indicated by 1 ogE is the same.

This is a kind of relativization (fiction) performed from the following viewpoint, and the inventors believe it to be reasonable.

That is, originally, in a photographic density characteristic curve, the X axis represents the logarithm of the exposure amount E (log, E = log I
) is positioned, and this corresponds to the fact that the discrimination characteristic of visual brightness and darkness is evaluated logarithmically and is linear (linearity, linear).From the above points, the above-mentioned D axis and I think that the relativization (fiction) of making the scaling the same is reasonable.

As shown in the examples below, this relativization (fiction)
Excellent results can be obtained in tone conversion of images. Incidentally, in the present invention, the above-mentioned graduation is a kind of simple method, and it goes without saying that the present invention is not limited to this.

As described above, the present invention provides D
The image information value (x
o value). The photographic density characteristic curves are shown in Table 1. value and x, value is x
=f(Dl is correlated by a mathematical formula, so the value of x, can be easily determined from the value of Dl.

In the manner described above, it is possible to easily obtain an image information value (xo value) that correlates with the amount of light incident on the photosensitive emulsion layer from the original image (subject).

Next, X at each pixel of the original image (subject) reasonably determined in this way. The gradation conversion formula (1
)> can be used to find the y value corresponding to each pixel.

In the present invention, the X axis (horizontal axis) that displays the x0 value, the y
As described above, when the skin values and the corresponding y values are plotted on the orthogonal coordinate system of the vertical axis in which the values are displayed, the gradation characteristic curve is obtained. To distinguish the present invention from the prior art:
The gradation characteristic curve is called an X-axis combination/decomposition curve, and the conventional one that emphasizes the density information value on the D-axis is called a D-axis combination/decomposition curve.

The characteristics of the X-axis decomposition curve obtained by the present invention and the conventional D-axis decomposition curve will be explained.

The gradation conversion formula (1) of the present invention is set under certain conditions, that is, α
, : IH, ys and γ values are respectively operated as constant,
In addition, by using multiple originals with different image qualities as color film originals (that is, each original has different density ranges and density information values), we calculated the X-axis combination and separation curves (gradation characteristics - When calculating, each of the obtained X-axis combination and decomposition curves (gradation characteristic curves) has a relatively same arrangement of y values from part H to part 8 of the final product (for example, a printed image). This is an extremely important feature of the present invention.In other words, as will be shown in the examples described later, image information correlated to the amount of light on the X-axis of each color film original Even if the value (y value) range is different (this reflects the difference in image quality of the color film original and is natural if the density range is different), the same predetermined X-axis When adjusted to
It means converging on a book (the only thing).

Therefore, from each X-axis combination/decomposition curve (gradation characteristic curve), for example, what kind of image quality will the final duplicate image have as seen from the arrangement of halftone dots (when the y value corresponds to the halftone dot area % value)? It is possible to accurately evaluate in advance whether the product will be obtained or not without the need for proof printing.

On the other hand, in the D-axis combination/separation curve, although a curve corresponding to each color film original is obtained, even if the same D-axis angle is adjusted on the D-axis as described above,
These are things that cannot be contained in a book (the only thing). In other words, each D-axis combination/separation curve merely indicates options for gradation conversion, and unless the proof is printed according to each D-axis combination/separation curve, the specified gradation conversion will be performed and a duplicate image of the desired image quality will not be produced. The relationship is such that it is not possible to accurately judge whether or not it will be done.

In relation to the above point, due to the nature of the gradation conversion formula (1) of the present invention, by arbitrarily changing Q + 'J H + 3'' + γ value (particularly by changing γ value), The shape of the gradation characteristic curve can be changed rationally, that is, the operator who manages the gradation conversion work can change the gradation of the reproduced image based on the gradation conversion formula (1). that it can be adjusted (modified, changed) as desired;
In other words, the gradation conversion work can be managed rationally based on the X-axis combination/separation curve.

The above describes how to obtain the image information value (y value) that correlates to the light intensity of a given pixel on the original image (subject) using the photographic density characteristic curve of the photographic light-sensitive material that is the recording medium of the color film original (media image). This is explained using an example of using .

In addition to the above-mentioned example (this is via a medium image), the image forming apparatus of the present invention can of course also process original images (subjects, objects to be imaged, printed matter in the usual sense of copying, etc.). It includes a device that directly detects the image information of the original (original) with the image information input sensor of the image forming apparatus and copies the image based on the detected image information. In such cases, the image information input sensor is a photomultiple, photodiode,
It is composed of a photoelectric conversion element such as a CCD or a two-dimensional CCD, and an image is formed (imaged) here to obtain image information correlated to the density required for forming a duplicate image. Therefore, in such an image forming apparatus, in order to detect true image information for reproduction from an original image, the photoelectric conversion characteristic curves of these photoelectric conversion elements (detection under a predetermined photoelectric conversion element) are used. Using a characteristic curve that defines the correlation between the image information value correlated to the density of the original image and the image information value correlated to the amount of light input to the charge conversion element from the original striped image, Find the basic light amount value (X),
Next, gradation conversion may be performed using <gradation conversion formula (1)>.

Note that when producing a duplicate image according to the present invention, the image information input sensor of the image forming apparatus described above, specifically, the TV
For various photoelectric conversion elements such as photoelectric conversion elements constituting camera image pickup tubes and two-dimensional CCDs used in electronic still cameras, etc., if their photoelectric conversion characteristic curves can be defined, existing performance ones will be sufficient. This means that a duplicate image with excellent gradation (density gradation and color tone) can be produced. In other words, efforts have been made to improve the characteristics (photosensitive characteristics and photoelectric conversion characteristics) of various photoelectric conversion elements and recording media (photosensitive materials) in an effort to produce high-quality reproduced images. When producing a duplicate image according to the invention, it is not necessarily required that various photoelectric conversion elements and recording media be sophisticated or have high performance, and the existing performance (characteristics) are sufficient, and this is adopted by the present invention. This is due to the characteristics of the gradation conversion method.

As explained above, when a duplicate image is formed by the image forming apparatus of the present invention, the gradation adjustment mechanism section has the above-mentioned
By incorporating hardware or software that performs gradation conversion based on gradation conversion formula (1), you can create reproduced images with excellent density gradation and color tone reproduction, or arbitrarily modify or change the image quality of original images. A duplicate image can be obtained.

At that time, the y value (gradation intensity value) obtained by the calculation process of <gradation conversion formula (1)> is determined by the density display method (variable dot method, constant dot method, variable density dot method) suitable for each image forming apparatus. It goes without saying that it is sufficient to adapt the display to a brightness display method.

For example, as shown in Figure 4, in the case of column (a) in Figure 4, the distribution of pixels recorded in a given pixel block becomes more dispersed within the pixel block as the number of recorded pixels increases. In addition to the positional relationship, it is also possible to make the dots gradually spread outward from the center of the pixel block in a spiral manner, in which case the dots will be similar to halftone dots in photolithography. Also, in the column of Fig. 4(b), (
A halftone dot with an area corresponding to the number of pixels in column a) is shown.

Although the pixel block has been described here as a 4×4 matrix type, 17 levels of gradation can be expressed by this.

- morphistically nXn matrix-type pixel block
+1 step of gradation (0 to 100%) is expressed.

This method of expressing the density gradation of an original image, such as a continuous tone image, by the distribution of pixels formed in matrix-type pixel blocks is a well-known method called the dither-matrix method. (For example, JP-A-58-
No. 85434.

No. 58-114569, No. 59-52969, No. 6
No. 0-141585, No. 62-186663, etc. ).

Note that the field of application of the image forming apparatus of the present invention will be explained here. Although the present invention has been described specifically in relation to the production of printed images, its application is not limited to equipment related to the production of printed images.

The image gradation conversion method, which is the most distinctive feature of the image forming apparatus of the present invention, has been described above particularly in relation to the production of printed images. However, the image forming apparatus incorporating the gradation conversion method is not limited to printing image production equipment. Representative examples of the image forming apparatus of the present invention will be described below, but the present invention is not limited thereto.

(il letterpress, lithography, halftone gravure, which has already been explained in detail,
Attempts to express the gradation and color tone of a reproduced image by modulating the size of the halftone dots (dots) found in printed images such as silk screens, piezoelectric inkjet, and thermal transfer images. This is also called area gradation method.) Image forming device.

(iii) Pigments and dyes such as printing inks that are deposited per pixel of a certain area (for example, per dot), which are also found in sublimation transfer type thermal transfer images, thermal development transfer images (using silver salt), conventional gravure images, etc. ), etc. (this is also called the density gradation method).

(iii) Digital copying machine (color copy, etc.)
, printers (ink jet type, bubble jet type, etc.), facsimiles, etc. Try to express gradation by changing the recording density per fixed area, such as the number of dots or ink particles (this is , said (
This method is similar to the area gradation method of il, and is also called the density modulation method. ) Image forming device.

[Equipment that adjusts the intensity of brightness per unit area to form CRT images, LCD TV images, etc. from electric signals related to image information such as IVL video signals, television signals, and high-definition signals, or that will be used for printed matter with gradation or hardware. Equipment that forms copies, etc.

(VlTV imaging equipment, electronic still camera.

Equipment related to image input (accumulation, storage) and transmission, such as facsimiles.

(In the original image and the reproduced image, it is not only possible to convert images in the equivalent density (luminance, @degree) range, but also to convert images in the spatially, luminance, wavelength, and temporally invisible range (e.g. Image captured by a high-sensitivity camera)
An input conversion device for image information in a low-light area where the density range difference between the original image and the reproduced image is small and the contrast is extremely low (in such cases, it is necessary to convert the image contrast rather than convert the image gradation). Emphasis is placed on emphasis transformation.)

(viil

(viii) In addition, a densitometer with a density/gradation conversion mechanism that displays density and halftone area %, etc., for preliminary inspection of color separation (for example, color proof for calibration)
and printing-related equipment such as color separation educational simulators.

and so on.

(Examples) Hereinafter, the present invention will be explained in more detail based on Examples, but the present invention is not limited to these Examples.

The main feature of the present invention is that the gradation conversion of an image, which is the core of the production of a duplicate image by an image forming apparatus, is performed under the above-mentioned gradation conversion formula (1). Therefore, first, an example of setting a color separation curve (gradation characteristic curve) that determines the quality of a reproduced image, which is a final product, will be explained. Here, setting examples and differences between the X-axis combination curve of the present invention and the conventional D-axis combination curve will be clarified.

Next, an image forming apparatus having a gradation adjustment mechanism incorporating hardware or software that performs gradation conversion based on gradation conversion formula (1) of the present invention will be described.

Example 1 (Setting of X-axis combination/decomposition curve) 1. Density characteristic curve used in the experiment The photographic density characteristic curve shown in FIG. thing)
It was used. In FIG. 1, the D axis (vertical axis) indicates the density value of the color original image. On the other hand, the X-axis is the exposure amount (logE=loglX t ) in the photographic density characteristic curve.
, but here it is quantified using the same scaling as the D axis. Further, the functional formula for the special photographic density curve was shown in Table 1.

2. Experimental original image The image quality of the color film original (medium image) may be either standard (appropriate exposure) or non-standard (over/under exposure) depending on the exposure conditions of the camera. ) and so on. In order to verify whether the present invention can be rationally applied to these widely different color film originals, we investigated the density range fDens of color film originals.
Experiments were conducted on samples with different ity Range=DR1 (different density ranges on the D axis).

3. Calculation of data for setting the X-axis combination/resolution curve Using the functional formula in Table 1, which is a function of the photographic density characteristic curve in Figure 1,
The D7 value on the D axis of various color film originals is
0 converted to a value, then the Xn value (gradation conversion formula (1
)> was converted into a gradation intensity value (y value).

The operating conditions for gradation conversion formula (1) are as follows: x=XI, -XHllyn=5%, 3'm=95%.

γ=1.00. β=IO−γ=0.1. α
=1.0Ok=γ/X, , -X□.

(In the case of Table 2 ■ below, X s-= 0.4781X
,,=z−z3oo. In other cases, see Table 2.) The results are shown in Table 2.

In Table 2, ■ to ■ in Table 2 are overexposed (light originals), ■ to ■ in Table 2 are close to appropriate exposure,
■ ~ [Phase] in Table 2 are underexposed (dark originals)
, respectively.

(Leaving space below) <Table 2> Data for setting the X-axis combination/separation curve for pale color originals (Part 1) Table 2> Data for setting the X-axis combination/separation curve for color originals with close to proper exposure (Part 2) ) Original DR = 0.50 to 2.80 Table 2> Data for setting the X-axis resolution curve for dark color originals (Part 3) Original DR = 0.30 to 3.00 4. X-axis resolution curve The data in Table 2 are shown in Figures 2 and 3.

In addition, in FIGS. 2 and 3, the vertical axis indicates the y value,
It must be noted that the characteristics of the horizontal axis are different.

The horizontal axis in Fig. 2 indicates the image information value correlated to the amount of light, and the
The horizontal axis of the figure indicates the density value of the color film original. In creating the graph, for convenience of comparison, a numerical value adjusted as a range regarding the same light amount and density (2.5000 in the case of this example) was used. The values after this adjustment are shown in Table 2 as (Dn, →) D,' , (Xn→
)x'. The adjustment to Do-D,' is the second
In the case of table ■, it is good. Similarly, skin -Xn' can be calculated as follows.

FIG. 2 shows the gradation characteristic curve according to the present invention, that is, the X-axis resolution curve (as described above, the relationship between Xn' and y), and FIG. 3 shows the D-axis resolution curve (as described above, , ' and y, which can be regarded as an example of setting a conventional color separation curve.

As is clear from Figures 2 and 3, an extremely surprising fact can be discovered. That is, no matter what image quality a color film original is used, the tone conversion formula (1)
〉α, ys.

It is a surprising fact that when the four values of ys and γ values are made the same, the respective X-axis separation curves converge into one identical curve as shown in Figure 2, and the color separation This is a fact that uniformly displays the tone of the color reproduction image that will be obtained later. That is, according to the technology for setting the gradation characteristic curve (X-axis position resolution curve) of the present invention, no matter what image quality a color film original is used, all y
A gradation characteristic curve is obtained with which a homogeneous duplicate image with the same value arrangement can be produced. In addition, an operator who intends to produce a duplicate image using an image forming apparatus may use the X-axis combination and decomposition curve obtained in the above manner to
The shape can be changed to a desired shape by changing the parameters, especially the γ value.

That is, the gradation can be rationally managed based on the above-mentioned X-axis combination/separation curve so as to obtain desired image quality and tone.

On the other hand, in the conventional color separation curve setting example shown in Fig. 3, although a D-axis separation curve corresponding to the image quality content of each color film original is obtained, It is not possible to accurately know in advance whether all images have the same tone from the respective D-axis integration and separation curves. That is, under the conventional D-axis combination/separation curve, it is difficult to know whether the image quality and tone of the final product are appropriate unless a proof is actually printed and evaluated.

This is due to the setup work in which an appropriate color separation curve must be selected from among a large number of color separation curves in the color separation work performed by the image forming apparatus, and the grooving work of color originals in the process before the setup work. means necessary. That is, the conventional D
Techniques for setting axial alignment and decomposition curves do not allow efficient implementation and management of gradation conversion work.

Embodiment 2 (Regarding Image Forming Apparatus) An image forming apparatus of the present invention will be described based on FIGS. 5 to 1O.

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

As shown in FIG. 5, the image forming apparatus of the present invention includes an image information input sensor unit that separates and reads transmitted light or reflected light of an original image into R (red), G (green), and B (blue). (detection unit) l and image information input sensor unit 1
The color separation unit 2 converts the output signal into color separation signals of Y (yellow), 9M (magenta), C (cyan), and K (black), and the gradation conversion formula (I) is used to determine the appropriate pixel. It has a gradation adjustment section 3 that obtains the density gradation according to the distribution of gradation, and an output section 4 that exposes the electrophotographic photoreceptor with laser light based on the output signal of the gradation adjustment section 3. The latent image is developed into a toner image in a developing section, transferred to a recording sheet, and fixed in a fixing section.

In order to form a color image, it is necessary to have separate photoreceptors and developing sections for each component color and transfer the formed toner images to a recording sheet sequentially, or to transfer latent images of the component colors onto a single photoreceptor. The procedure is to form and develop a toner image, transfer it to a recording sheet, and repeat this process for each color component.

The image information input sensor unit l detects transmitted light or reflected light from each part of the original 5 using a photoelectric conversion element such as a photomultiplier or a solid-state image sensor (CCD), and outputs R, G, B, and U as current.
Each SM signal is output, and the A/V converter 6 converts this signal into a voltage signal.

The color separation section 2 uses a log amplifier 7 to logarithmically calculate the voltage signals of R, G, B, and tJsM of the image information input sensor section 1, convert them into densities, and perform basic masking (B
M) In step 8, the black (K) component is separated from this density, and further the Y, M, and C components are separated. That is, in the image forming apparatus of the present invention, an object to be reproduced (printed matter, etc.)
is first recorded or accumulated in an image information reading mechanism composed of a photomultiplier or a CCD in the image information input sensor section 1, and density information values (shi) are obtained as image information of the object to be reproduced in the color separation section 2. be done. This is determined for each color component of Y, M, and C as described above. Next, the density information value (It,) is
Using the photoelectric conversion characteristic curve of D, the image information value (Xn) correlated to the light amount is converted into a basic light amount value (X). These may be performed using software or hardware (not shown). Further, a function of determining an image information value (Xn) correlated to the light amount from the density information value (Dn) may be incorporated into the adjustment section 11, which will be described next.

Note that FIG. 5 shows a color correction (CC) section 9 as a configuration of the color separation section 2. As shown in FIG. Here, R
, G.B. and Y.M.

The Y component 2 components and the C component are controlled for each C original color, and the black component of the original is controlled by the U CRfunder colorremova of the UCR/UCA section 10.
ll, or U CA (under color
In additionl, the ratio expressed by the three components Y, M, and C is determined. In this way, the Y, M, and C components converted into image information values correlated with the amount of light are conventionally processed by adjusting the area ratio ye occupied by the pixels of each component in the gradation control section in the gradation adjustment section (IMC).
, tae , ce , ke' and invert this
However, in this embodiment, the adjustment section 11 is used instead of the gradation control section and the inverse log conversion section, and here, from Y, M, C, K to ye, ate,
Conversion to ceke' is being performed. The adjustment unit 11 has an algorithm of <gradation conversion formula (1)> inside, and has Y, M
, C, respectively, to obtain ye, Ile, ce, and ke'.

The adjustment unit 11 is a general-purpose computer that has the algorithm of gradation conversion formula (1) as software and has an A/D and D/A I/F (interface), and a general-purpose IC that uses the algorithm as internal logic. It can take various forms, such as an embodied electrical circuit, an electrical circuit including a ROM that stores the calculation results of the algorithm, a PAL that embodies the algorithm as internal logic, a gate array, and a custom IC. In order to form an image with a laser beam corresponding to the density of the original image, the diameter and intensity of the laser beam are kept constant as described above, and the image is formed within an image block corresponding to the area of halftone dots in the case of photoengraving. The number of unit pixels and their distribution are calculated and the data is output.

The area ratio (gradation intensity value) of the pixel obtained by the adjustment unit 11 is input to the color channel selector 12, and the color channel selector 12 selects ye, me, ce.
, ke' are output selectively. This output is A/
The signal is A/D converted by the D converter 13 and input to the output section 4 . In the output section 4, a dot control section 14 controls the laser beam based on the output of the gradation adjustment section 3.

FIG. 6 shows an image forming apparatus according to a second embodiment, in which the conventional inverse log conversion section 15 is used as is, and therefore, in the adjustment section 11, ye, me, ce are converted in logarithmic form.
, ke' are output. This allows you to convert just one component in conventional equipment using the gradation conversion formula (
1)> can be applied, and an existing system can be modified to a system according to this method with fewer changes than that according to the first embodiment.

FIG. 7 shows an image forming apparatus according to a third embodiment,
The conventional gradation control (IMC) section 16 is left as is, and the connection between the inverse log conversion section 15 and this gradation control section 16 is cut off. and the adjustment part similar to the second embodiment, i.e. ye, +me in logarithmic form.
An adjustment section 11 that outputs ce and ke' is employed.

The adjustment section 11 takes the Y, M, C, signals from the stage before the gradation control section 16, and converts them to an inverse log conversion section 15.
The value after conversion is output.

FIG. 8 shows an image forming apparatus according to a fourth embodiment,
The inverse log conversion section 15 and the color channel selector 12 are left as they are, and the connection between them is cut off. That is, the adjustment section 11 has Y and M from the stage before the gradation control section 16.

C, and directly selects the color channel selector 12.
is connected to ye, lee, Ceke' without being constrained by the conventional system, ye, me,
ce and ke' can be obtained. As in the third embodiment, the system can be implemented by making slight modifications to the conventional system.

FIG. 9 shows an image forming apparatus according to a fifth embodiment,
The entire conventional gradation conversion section is configured as a new adjustment section 11, and <gradation conversion formula (1)> can be applied to this adjustment section.

In the examples shown in Figures 5 to 9, the image forming section is of an electrophotographic type that forms an electrostatic latent image on a photoconductive photoreceptor by scanning a laser beam, but a recorded image is formed by the distribution of pixels. As a method, other methods such as electrostatic recording type, magnetic recording head, etc. can be adopted.

In electrostatic recording, as shown in Figure 10, each electrode of a recording head has a large number of electrodes arranged in close proximity to or in contact with a recording body made of a moving sheet-like dielectric material in a direction perpendicular to its moving direction. A voltage is applied to form an electrostatic latent image. The steps after the step of adding toner to this latent image and developing it are the same as in the case of electrophotography. The dot control unit 1 of the output unit 4 for the recording head as an assembly of electrodes.
4, a voltage is applied as an output signal corresponding to the image to be recorded. In addition, in the magnetic recording type, the recording medium is, for example, a drum whose surface is uniformly coated with a magnetic material, and a voltage as an image information signal is applied to the magnetic recording head in contact with the surface. A magnetic latent image is formed on the recording surface by relatively moving the recording surface and the recording surface. In order to develop this latent image, a toner made of magnetic material is used, but otherwise the process is carried out in the same manner as in the case of electrophotography.

If you modify the gradation adjustment section of conventional equipment as described above,
It is also possible to integrate the <gradation conversion formula (1)> with other processing, and by optimizing the system, speeding up and compactness can be realized, and cost performance per system can be improved.

In the above embodiment, the color separation section has the same configuration as the conventional one, but by using <gradation conversion formula (1)>, the color correction (CC) section 9 and the USR/UCA section 10 are no longer necessary. If not, a color separation unit may be used in which these are omitted.

Furthermore, descriptions of commonly used effects, such as blur masks and sharpness effects that are not directly related to the present invention, are omitted in the above embodiments regarding the image forming apparatus.

〔Effect of the invention〕

The present invention has the following excellent effects.

l) The most basic matter in producing a duplicate image is the density value of a predetermined pixel on the original image such as a continuous tone image and the reproduced image (image recorded by the pixel distribution) to be produced. In the past, determining the correlation between the gradation intensity value of the corresponding pixel was based solely on the experience and intuition of the operator, or based on a limited number of stator data (an irrational method). In contrast, in the present invention,
No matter what the conditions are, we can use this as the gradation conversion formula.
(1)> can be determined rationally. Furthermore, when converting an original image such as a continuous tone image into a duplicate image based on pixel distribution, the most important elemental technology, gradation management (gradation conversion, modification, or change), is simply a matter of image density. Since it is directly related not only to the gradation but also to the tone of the image, the density gradation and color tone can be managed rationally according to the present invention. That is, an image forming apparatus that incorporates the algorithm of the present invention's gradation conversion formula (1) in its gradation adjustment mechanism theoretically and rationally systematizes the gradation conversion work (color separation work) and performs the process. The work can be simplified and the effect is extremely large.

2) By incorporating the algorithm of <gradation conversion formula (1)> into the gradation adjustment mechanism of the image forming apparatus, the image forming apparatus can be rationalized and simplified, and manufacturing costs can be reduced.

In addition, the operation is simplified and clarified, the number of reworks is extremely reduced, the consumption of consumable materials is greatly reduced, and the performance of the image forming apparatus is greatly improved. In particular, in terms of the performance of the image forming apparatus, it has the great advantage of being able to form duplicate images with excellent gradation and color tone, regardless of the quality of the original image.

3) A gradation adjustment mechanism that incorporates the algorithm of ``gradation conversion formula (1)'' allows for the standard for evaluating the quality of recorded images based on pixel distribution to be rationally and easily separated from the image information of the original image. can do. Therefore, it is possible to rationally respond to the diversified needs of customers.

4) By adopting the gradation conversion formula (1), we can improve the education and training of engineers, which is currently required as image creation equipment such as printers and copiers become more sophisticated. ) can be carried out effectively through the operation of the system, which can save unnecessary effort in daily work and free up time for new creative development.

[Brief explanation of the drawing]

FIG. 1 shows a photographic density characteristic curve of a color film. FIG. 2 shows an X-axis position resolution curve (used in tone conversion of the present invention) set based on the photographic density characteristic curve of FIG. 1. FIG. 3 shows a D-axis position decomposition curve (used in conventional gradation conversion) set based on the density characteristic curve of FIG. 1. FIG. 4(a) shows an example of expressing the density gradation of a continuous gradation original image by the distribution of unit pixels within a pixel block, and FIG. FIG. 3 is a diagram showing a case in which density gradation is expressed by the size of halftone dots in photoengraving corresponding to the case. FIG. 5 is a block diagram of an image forming apparatus according to a first embodiment of the present invention. FIG. 6 is a block diagram of an image forming apparatus according to a second embodiment. FIG. 7 is a block diagram of an image forming apparatus according to a third embodiment. FIG. 8 is a block diagram of an image forming apparatus according to a fourth embodiment. FIG. 9 is a block diagram of an image forming apparatus according to a fifth embodiment. FIG. 10 is an explanatory diagram of an image forming section in an electrostatic recording type. ivy 1 diagram

Claims (1)

[Claims] 1. In an image forming apparatus for forming a duplicate image from an original image, (i) an image information input sensor section of the image forming apparatus is correlated to the amount of light input to the sensor from the original image; Using the photoelectric conversion characteristic curve of the sensor that defines the relationship between the image information value (X_n) and the image information value (D_n) correlated to the density output from the sensor, (ii) The gradation adjustment section of the image forming apparatus is configured to output image information value (X_n) correlated to the light amount of the original image obtained as described above; The value (X_n) is calculated using the following <gradation conversion formula (1)>
An image forming apparatus for forming a duplicate image with excellent gradation reproducibility from an original image, characterized in that the image forming apparatus is configured to convert an original image into a gradation intensity value (y value) for gradation adjustment. . <Tone conversion formula (1)> ▲There are mathematical formulas, chemical formulas, tables, etc.▼ [However, in the above <Tone conversion formula (1)>, X: (X
_n−X_H_n). This is calculated from the image information value (X_n) correlated to the light amount of the corresponding pixel, which is determined from the density information value (D_n value) of an arbitrary pixel on the original image using the characteristic curve. This is the basic light quantity value obtained by subtracting the image information value (X_H_n) correlated to the light quantity of the corresponding brightest part obtained via the characteristic curve from the density information value (D_H_n) of the part (H part). y: Gradation intensity value set to a pixel on the duplicate image corresponding to an arbitrary pixel on the original image. y_H: gradation intensity value preset for the brightest part (H part) on the original image. y_S: gradation intensity value preset for the darkest part (S part) on the original image. α: Surface reflectance of image representation medium for forming a reproduced image. β: Numerical value determined by β=10^-^γ. K: γ/(X_S_n - X_H_n) However, X_S_n is an image correlated to the light amount of the corresponding darkest part obtained from the density information value (D_S_n) of the darkest part (S part) on the original image via the characteristic curve. Indicates the information value (X_S_n). γ: arbitrary coefficient. respectively. ] 2. The image information input sensor section of the image forming apparatus is used as a record where the original image has a predetermined characteristic curve (one that defines the relationship between the image information value correlated to the density and the image information value correlated to the amount of light). When the image is recorded on a medium, the image information value (D_n) correlated to the density measured by the sensor section is inputted to the recording medium in order to form a document image using the characteristic curve of the recording medium. 2. The image forming apparatus for forming a duplicate image according to claim 1, wherein the image forming apparatus is configured to output an image information value (X_n) correlated to the amount of light generated. 3. The image forming apparatus for forming a duplicate image according to claim 1, wherein the image information input sensor is constituted by a photoelectric conversion element such as a photomultiplier, a photodiode, a CCD, or a two-dimensional CCD. 4. The image forming apparatus for forming a duplicate image according to claim 2, wherein the recording medium is a photographic light-sensitive material and the characteristic curve is a photographic density characteristic curve. 5. The image forming apparatus according to claim 1, wherein the image forming apparatus is a device having a function of forming a duplicate image from an original image, such as a plate-making device, a copying device, a printer device, an image transmission device, a TV imaging device, an electronic camera device, etc. An image forming apparatus for forming a duplicate image of.