JPH0414382A - Laser beam printer - Google Patents

Abstract

PURPOSE:To generate a copy picture with excellent reproduction in gradation and color tone by using a prescribed equation so as to convert density informa tion of a picture element of an original picture into gradation intensity of a picture element on a relevant copy picture. CONSTITUTION:A density information Dn of original picture is converted into picture information Xn in relation to a luminous quantity corresponding to each picture element value Dn by utilizing a density characteristic curve specify ing the relation between a density information D of an original picture of the recording medium with an original picture and the picture information value X in relation to a luminous quantity mode incident in a recording medium from the original picture. Moreover, the picture information Xn is converted into gradation information Y according to gradation conversion equation Y=YN +a(1-10<->KX)(YS-YH)/a-b, where X=Xn-XNn, XNn is a basic luminous quantity subtracting picture information XHn of a brightest part from density information DHn of a brightest part H on an original picture, Yn is a gradation intensity of a darket part S on an original picture, (a) is a surface reflectance of copy picture recording paper, (b) is a numeral decided by b=10<->C, K=C/XSn-XHn, XSn is picture information of the part S and C is an optional coefficient.

Description

[Detailed Description of the Invention] [Objective of the Invention 1 (Field of Industrial Application) The present invention converts an image information signal obtained from an original image using a new gradation conversion method, thereby achieving excellent gradation reproducibility. The present invention relates to a laser beam printer capable of forming reproduced images.

Specifically, the present invention is capable of handling various original images (in the present invention, all objects to be reproduced on recording paper are original images. In the present invention, points to be kept in mind are as follows:
An original image is an original image in the usual sense, for example, when creating a duplicate image from a monochrome or color photographic image or a video signal (TV) image, these images themselves become original images, and furthermore, In some cases, the original subject such as a landscape, still life, or person, or the imaged object itself, that is, the original image, is sometimes referred to as a manuscript image.

), the true image information value is obtained from the original image, and this is converted using a gradation adjustment mechanism using a new gradation conversion formula. This invention relates to a laser beam printer that can form a reproduced image with excellent gradation and color tone reproducibility on recording paper based on the output signal (X).

More specifically, the present invention provides image information values to various image information input media (e.g., photosensitive material, two-dimensional CCD, photomultiply, photoprinter, etc.) when producing a duplicate image from an original image using a laser beam printer. Photoelectric conversion elements such as diodes and CCDs are used.)
(In the present invention, the images on these input media are collectively referred to as media images in comparison with the original images. Note that the original images are not recorded or stored in manual media. (This also applies to cases in which the sheep is processed to obtain image information values without media images), density information values obtained from media images (this should be interpreted in the broadest sense as described below) ), instead of using image information values correlated to the amount of light input to the input medium to form a medium image from a document image, such image information values are converted into a new gradation conversion formula. It is an object of the present invention to provide a laser beam printer having a gradation adjustment mechanism that performs conversion processing.

(Prior art) When duplicating an image from an original image with continuous gradation such as a photograph, photosensitive paper is used as a recording sheet, which corresponds to the original (subject) by analog processing (exposure) of the original (subject). An image with continuous gradation is formed (silver halide photographic recording). On the other hand, laser beam printers that digitally record images on plain paper rather than photosensitive paper do not form images using the analog processing described above, so 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, many efforts are being made to improve the reproducibility of gradations and color tones in laser beam printers. Forming a duplicate image using a laser beam printer is similar to the method of converting continuous gradation to halftone gradation in photolithography in printing, in which the original image with continuous gradation such as a photograph is obtained by photoelectric scanning. The purpose of this method is to process the density information values and use the signals to form on recording paper an image consisting of a pixel distribution having gradation and color tone corresponding to the original image.

However, current laser beam printers are unscientific in their gradation adjustment methods for processing the density information values obtained from the original image so that the density gradation is correctly reproduced in the reproduced image. (Currently, the reproducibility of density gradation and the color tone closely related thereto cannot be achieved.

As is well known, the density gradation of a duplicate image depends on the pixel density display method. There are two ways to display such pixel density gradations: one is to change the pixel coverage rate by changing the size of the dot (size modulation method, variable area dots), and the other is to change the pixel coverage by changing the size of the dot (size modulation method, variable area dot method), and by changing the pixel coverage rate by changing the dot size (size modulation method, variable area dot method). There is a method of changing the pixel coverage (density modulation method, constant dot method).

However, as described above, when attempting to reproduce a document image using a conventional laser beam printer, for the density information value of a predetermined sample point (pixel) on the document image,
The pixel coverage rate (ratio of recording to the number of unit pixels constituting a pixel block), that is, the pixel coverage rate, is determined by the diameter and density of the dots on the corresponding replicated image. 1m (
Hereinafter, this will be referred to as the gradation intensity value of the pixel or simply the gradation intensity value. ) and how to obtain the tone intensity value of such a pixel.
The current situation is that no scientific study has been conducted.

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 at present, equipment manufacturers have no choice but to rely on what has been determined in advance based on experience, intuition, or an unparalleled 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). However, it has not been possible to develop a laser beam printer that is flexible enough to make changes (changes and corrections in color tones).

This is how conventional laser beam printers use the density information value of a predetermined pixel on the original image, which is an extremely important image information value when producing a duplicate image, to the gradation intensity value of the corresponding pixel on the duplicate image. It means that it is impossible to scientifically and rationally transform something into something.

(Problem to be Solved by the Invention) The cause of the above-mentioned problems in conventional laser beam printers 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 established a rational image gradation conversion technology in order to ultimately streamline the image forming process and produce reproduction images of excellent quality. Based on the basic understanding that we must do this, we conducted extensive research.

As a result, when producing a duplicate image using a laser beam printer, the image information detection (reading) mechanism of the printer, more specifically, a recording medium such as a CCD, uses the image information value as essential for image reproduction. Instead of the conventional method of using image information values obtained from recorded media images, the image/image information value of the object (original image) that is the real object of reproduction is obtained, and this method It has been discovered that when the image information values obtained in this manner are processed using a specific gradation conversion formula to obtain gradation intensity values, a reproduced image with extremely excellent density gradation reproducibility can be produced.

As mentioned above, in the present invention, importance is placed on what kind of image information value to use as essential for image reproduction, and image information values different from those in the past are adopted. ing.

In order to clarify this from the perspective of the image to be reproduced, in the present invention, the boundary between before and after the reproduction target is recorded or stored in the recording medium system that constitutes the laser beam printer image information acquisition mechanism, The object that is the true target of file reproduction is called the original image or real image that forms the source of the media image (usually called the original image, but also called the real image to emphasize the features of the present invention. (In some cases, the original image is regarded as the subject or imaged object, so it is also referred to as the object.), The object recorded or accumulated on the recording medium system is
It is called a media image.

That is, in the present invention, the image information value of the original image to be used when converting the density gradation is the density information value obtained from the medium image (this can be any physical quantity correlated to density as described later). ), but rather defines the relationship between the density information value of each recording medium and the image information value correlated to the amount of light from the original image incident on the recording medium. (hereinafter, in the present invention, regardless of the recording medium system, the above-mentioned characteristic curve of each recording medium system is collectively referred to as the density characteristic curve). It is a value. According to the present invention, when converting the image information values correlated with the light amount using a specific gradation conversion formula to obtain gradation intensity values for gradation conversion, It is possible to obtain a duplicate image in which not only the image characteristics but also the image characteristics are arbitrarily modified or changed.

In the present invention, as described above, the original image (substantive image)
It must be noted that """ refers to the literal original image that is the true object of reproduction, and is distinct from media images recorded or stored on various recording media.

The present invention improves the conventional reproduction image production technology that emphasizes density information values obtained from media images recorded on various recording media, and improves the original image that should be the true object of reproduction (substantive image). This technology incorporates a completely new reproduction image production technology that emphasizes the image information value of the original image, that is, the image information value that correlates with the amount of light that enters the recording medium system from the original image, and in particular, incorporates the image gradation conversion technology that is the core technology. The aim is to provide a laser beam printer with a high degree of complexity.

C Structure of the Invention] (Means for Solving the Problems) To summarize the present invention, the present invention provides a method for obtaining density information values of each pixel of a document image from a medium image in which the document image is recorded on a predetermined recording medium. and a laser beam printer for processing the density information value with a gradation adjustment mechanism and forming a duplicate image having one color or multicolor halftones on recording paper based on the processed signal, The adjustment mechanism transfers the density information value (Do value) of each pixel of the fil original image to the recording medium from the density information value (D value) unique to the recording medium on which the original image is recorded and the original image. The density information value (D
The image information value (X, value) is correlated to the light amount corresponding to the n value)
(□,) Furthermore, the image information value (Xn value) correlated to the light amount is converted into a gradation intensity value (cy value) for gradation adjustment using the following <gradation conversion formula (1)>. This invention relates to a laser beam printer characterized by:

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

First, the theoretical background 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 problem of gradation conversion during the production of printed images, which is a particularly typical field of technology for producing reproduced images. Much will be explained in relation to production techniques using scanners (monochrome and color scanners). However, this is for convenience of explanation, and since there are similar problems in tone conversion in laser beam printers, the value of the tone conversion theory of the present invention explained here is limited to these problems. Nothing diminishes its value when built into a laser beam printer.

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.
ion control and color correction (correction) technology (c
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. Regarding the (original image), the density characteristics from the brightest part to the darkest part are not pushed rationally, and the density characteristics that are essential for converting the density characteristics of the original image into a reproduced image with 1:1 fidelity. The basic understanding is that the determination of the correlation between images (original image and duplicate image) (one-tone conversion formula) 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. Pat. 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 due to the fact that, as mentioned above, the true target of a duplicated image should be the original image (substantive image); In order to obtain image information values for reproduction from a manuscript image (substantive image), the manuscript image is first recorded on a predetermined recording medium of a device for producing a reproduction image (i.e., it is not used as a medium image), This means that tone conversion of the image is performed using the density information value obtained from this as a clue. This depends on the photosensitive characteristics and photoelectric conversion characteristics of the recording medium, and does not mean that the image information value of the original image (substantive image) itself is used.

This will be explained using an example in which a color print image is produced as a duplicate image.

A color film original is a medium image referred to in the present invention, in which an image of a still life, a person, etc. is photographed on a recording medium called a photographic light-sensitive material. Therefore, when density information is detected from a color film original (medium image) and used for image gradation conversion, it is no longer based on the image information value of the subject (substantive image). That is, in the conventional printing image production technology using a color film original (media image),
When light qt enters the photographic light-sensitive material (photosensitive emulsion layer), which is a recording medium, from the subject under predetermined exposure conditions (as is well-known, when the conditions are the intensity I of the incident light and the incident time, the exposure HE is Color separation work (color separation work includes both the above-mentioned color correction and gradation control) is performed based on the density information value of the photographic image recorded in E=It.

As is well known, photographic materials on which subjects have been photographed have a photographic density of iphotographic dens through development.
ityl is formed and this is what becomes the media image. The curve representing the correlation between the photographic density (degree of blackening) and the exposure amount E of the photographic light-sensitive material described above is the photographic density characteristic curve iph.
otographic characteristic
It is a curve. This is the photographic density fDl on the vertical axis.
(D=log IO/I), and is displayed with the logarithm value (logE) of the exposure amount E taken on the horizontal axis. In addition, for film and dry plates (transparent originals), the ratio between the intensity of transmitted light ■ and the intensity of incident light ■ 0, 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). ) is well known.

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 is based on the photographic material from the subject. (Hereinafter, in the present invention, the absolute value of the exposure amount may be used or the relative value may be used as described later, so the amount of exposure incident on the amount of light is hereinafter referred to as "image information value correlated to the amount of light" in a broad sense.) ), that is, it is not a color separation technique assembled from the standpoint of the horizontal axis (image information value correlated to the amount of light) of the photographic density characteristic curve. The density information value of a color original image, which is the basis of the color separation work in the prior art, is different from the image information value that correlates with the light amount of the subject (substantive image), as is clear from the shape of the photographic density characteristic curve. For example, the image information of the subject is not provided linearly. ), the appearance of separation between the two may vary widely depending on changes in given conditions such as exposure conditions and development conditions.

In other words, since it is affected by the photosensitive characteristics of the photosensitive flower material used as a 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 (substantive image). is a linear relationship (for example, 1:1 of 4
5° linear relationship).

On the other hand, it is well known that human vision has a logarithmic discrimination characteristic for brightness and darkness, and it is well known that humans distinguish between brightness and darkness based on the above-mentioned discrimination characteristic of the amount of light that enters the visual system from an object (substantive image). is being evaluated. Here, the gradient of concentration change? We perceive things that are linear as being natural.

Therefore, in producing a color printed image, the density value (D=log ■0 of the medium image recorded on the photographic light-sensitive material)
/I) If you proceed with the work based on the clue, you will be using the density information value after being influenced by the photosensitive characteristics of the photosensitive flower material for photography, and you will be using the density information value that has been influenced by the photosensitive characteristics of the photosensitive flower material for photography. This does not mean that image information values that are correlated to the amount of light are used.

Based on the above-mentioned situation, the present inventors used various image recording media (photosensitive flower materials, two-dimensional CCD, photomultiply, photodiode, etc.) to produce duplicate images.
The original image (which is the true object of reproduction) can be reproduced without using the density information value of the medium image, which has already been affected by the photosensitive characteristics and photoelectric conversion characteristics of the photoelectric conversion element (such as a CCD).
first-order (raw, primordial) from a real image, subject)
We conducted extensive research on methods for producing various types of duplicate images based on image information values that correlate with light intensity.

As a result, in the production of printed images, (1) using the photographic density characteristic curve, the vertical axis (Dlog
Find the value of the horizontal axis (logEl) from the value of IO/I
Hereinafter, the vertical axis will also be referred to as the D axis, and the horizontal axis will also be referred to as the X axis. ), in other words, the density information value (D value) on the D axis of the color film original (medium image) from the brightest part to the darkest part defined on the photographic density characteristic curve is projected onto the X axis. Find the image information value (X value) on the X axis, (2) More specifically, calculate the density value (Dn value) of any pixel on the medium image on the D axis via Image information value (X, value) of the corresponding pixel projected on the axis (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 light amount."

), and then (3) X obtained as described above. Based on the x0 value and using the specific gradation conversion formula previously proposed by the present inventors, the gradation intensity value indicating the halftone area % value is calculated from the x0 value. We have discovered that when the size is controlled, it is possible to obtain printed images with excellent halftone gradation and image characteristics that are faithful to the subject (substantive image).

In the image gradation conversion of the present invention, when converting the density information value of an arbitrary pixel on the original image (substantive image) into the gradation intensity value of the corresponding pixel of the reproduced image, as described above, various recording media can be used. Density information values obtained from recorded or stored media images are not used as they are. In other words, the image information value of the original image (substantive image, real scene) that is the true target of duplication, which is not affected by the photosensitive characteristics and photoelectric conversion characteristics of the recording medium system, is calculated based on the density information value (the image information value that is incident on various recording media from the subject). The point is that this is a completely new gradation conversion in which the image information value (correlated to the amount of light) is calculated, and this is processed using the gradation conversion formula (l) described above to convert it into a gradation intensity value. It has great characteristics.

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

In a duplicate image formed by a laser beam printer, the basic components that make up the duplicate image are the gradation intensity value at a predetermined pixel and the image forming material (toner).
This is because human vision has the ability to easily identify, for example, a 1% difference in the size of halftone dots in a printed image as a density difference. Thus, as an image forming means, 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. For example, if we focus on a dot set at a certain pixel and examine the effects that changes in the amount of ink applied to the dot and changes in the size of the dot have on the density gradation, we find that the latter How to set the gradation intensity value is an extremely important issue in the production of reproduced images with excellent gradation reproducibility.
Replicated images with excellent density gradation reproducibility also have excellent color tone reproducibility, and this can be confirmed in many cases.

In addition, in connection with the above, when attempting to produce a duplicate image using a laser beam printer, 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 complicated and unstable factors be built into the laser beam printer.

For this reason, when producing a duplicate image with halftones using a laser beam printer from an original image such as a 5-continuous-tone image, it is necessary to The gradation intensity value (y8) of the pixel in the darkest part (S) can be arbitrarily selected, and the density gradation of the image from the brightest part (H) to the darkest part (S) can be rationally and easily selected. It is absolutely necessary to have a means of coordinating and managing the situation.

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.

The above-mentioned previously proposed halftone dot area percentage value (y) used when producing a printed image is calculated using the gradation conversion formula (as mentioned above, the basic framework is based on the present invention). (This is similar to gradation conversion formula (1), but its operating conditions are completely different.) can be derived from generally accepted density formulas (photographic density, optical density). That is, it can be induced by applying the following.

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

Ten halftone dots surface dot × ink surface reverse N sheep It is possible to arbitrarily set halftone dots of desired size on the H and 8 parts of the printed image using this density formula (D') related to plate making and printing. Then, the basic density value (x) at an arbitrary sample point on the continuous tone image (original image) and the corresponding halftone dot at the sample point on the halftone image (printed image). Incorporating the requirement to rationally relate the numerical value (y) of the point area percentage, the theoretical value and the measured value are derived to closely match, and the obtained value is expressed by the following formula. Formula (2)>.

<Tone Conversion Formula (2)> When applying the above <Tone Conversion Formula (2)> to tone conversion of an image when producing a printed image, α.

While arbitrarily selecting the 3/H, 3/It, and γ values, calculate the value of the halftone dot area percentage (7tons) at the corresponding pixel on the printed image from the basic density value (x) of any pixel on the original image ( It is operated to find 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 standard plate C is used as 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 halftone gradation characteristic curve (obtained by graphing the y values and y values described above), which is the work standard for converting the density information value of the original image into the halftone area value of the printed image. (This is the standard curve for converting continuous gradation to halftone gradation.) Once the halftone gradation characteristic curve of other color plates is determined, It can always be determined rationally by multiplying the value by an appropriate adjustment value based on the gray balance ratio of each color of printing ink. It goes without saying that the halftone gradation characteristic curves for each color plate determined in this way are each reasonable characteristic curves, and furthermore, the mutual relationship between the characteristic curves in terms of gradation and color tone is also correct. be 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. It is also possible to rationally adjust the color tones in this relationship. 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 the theory behind the gradation conversion work using the above-mentioned gradation conversion formula (2) is based on the laser Needless to say, this method can also be used to produce duplicate images using a beam printer.

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

On the other hand, in the gradation conversion of an image suitable for producing a duplicate image using the laser beam printer of the present invention, in order to achieve better density gradation conversion, the original image ( Instead of using the conventional density information value as the image information value of the real image), the image information value correlated to the amount of light of the subject is used. In order to perform the gradation conversion of the present invention, which is different from the conventional one described above, the operational conditions of ``gradation conversion formula (2)'' are summarized as ``gradation conversion formula (1)''.
)> Needless to say.

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

In the operation of the above <gradation conversion formula (1)> of the present invention, the basic light amount value (x) must be determined from the medium image in which the original image (substantive image) is recorded on a predetermined recording medium. As described above, the basic light amount value (x) is determined by the density information value (fl) of a predetermined pixel on the original image via the density characteristic curve of the predetermined recording medium on which the original image is recorded or stored.

value).

In the present invention, the density information value may be any value that reflects the physical quantity related to the density of each pixel of the medium 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 02 to 270 on the vertical axis.
The value on the horizontal axis corresponding to this is adopted. ), also yH[
gradation intensity value set for the brightest (H) pixel] and ys
If a percentage value (for example, 5% or 95% pixel coverage) is used for the gradation intensity value set for the pixel in the darkest part (S) of C, the y value [corresponding to any pixel on the original image] The gradation intensity value set for the pixel on the duplicated image] is calculated as a percentage value.

In the operation of the above <gradation conversion formula (1)> 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.

kX y:yH+IE (110N ys yo) 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 set to 1.0 if the zero point adjustment of the density measuring mechanism is performed using the recording paper as a reference.

Further, according to the modification (α=1.0), it is possible to set yH in the brightest part H and y3 in the darkest part S on the reproduced image by the laser beam printer as planned.

This means that in the brightest part H on the duplicated image, x=O, and in the darkest part S, X=[Xs,, -X14
This is clear from the fact that -kX=-γ.

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 β=io'' as described above) take various values.In the present invention, by appropriately selecting these numerical values, the original image Regardless of the quality characteristics of the image, the gradation conversion process of the image can be performed rationally.

That is, the image gradation conversion processing method based on the above-mentioned gradation conversion formula (1) 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 above-mentioned gradation conversion formula (1) of the present invention also has the following features: a, β, This is extremely useful for rationally changing or correcting the characteristics of an original image by appropriately selecting the γ value, and furthermore, the ys and Xs values. Of the parameters in tone 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) This is easy to understand if you put it into practice.

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, i.e., color Colors such as reflected light from the original are blue (B).
), green (G), and red (R) to obtain a signal correlated to the density information value (β value) for each color, and convert this into an image information value (y value) correlated to the amount of light. Furthermore, processing is performed by a gradation adjustment mechanism using the above-mentioned <gradation conversion formula (1)>,
The recording section of the laser beam printer may be adjusted based on this processing information value (y value) to form an image. At that time, by calculating the y value for the standard color plate (for example, 6th plate), that is, the gradation characteristic curve (y value) of the standard color plate, and plotting the y value against the y value, the above-mentioned printing A gradation characteristic curve similar to the halftone gradation characteristic curve in the technology can be obtained.), and the gradation characteristic curves of the other color plates (M plate, Y plate) are determined based on the y value of the standard color plate. , the gray color of each ink.
Since it can be determined rationally based on the balance ratio (multiplying by an appropriate adjustment value), 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 (])〉, so it is not only a reasonable characteristic curve, but also a gradation between those characteristic curves. The interrelationships regarding tone and color tone are also reasonable and appropriate.

Next, using the density characteristic curve of each recording medium, an image information value (y value) correlated to the amount of light incident on each recording medium is obtained from the density information value (β value) of an arbitrary pixel on the original image. We will explain how to find it.

In the present invention, in order to obtain image information values, especially density information values, for gradation conversion from an original image (substantive image), the original image is recorded on various recording media, such as a photographic light-sensitive material, a two-dimensional CCD, a photosensitive material, etc. circle, photodiode, C
A medium image is recorded on a recording medium referred to in the present invention, such as a photoelectric conversion element such as a CD. Then, from the density information value (D value) at each pixel of the original image, the density characteristic curve unique to each recording medium (the density information value read by the recording medium system of the original image and the original image incident on each recording medium) is calculated. The image information value correlated to the light amount of the corresponding pixel (characteristic curve that defines the relationship between the image information value correlated to the light amount from
X value) must be found. For this purpose, the density characteristic curve of each recording medium must be accurately or approximately converted into a function (mathematical expression).

Here, we will explain how to formulate a photographic density characteristic curve using color as an example using a color film original (medium image) whose recording medium is a photographic light-sensitive material. The expression can be expressed in the same way. It should be noted that when using a color film original (media image), the true object of reproduction (original image) is the object (substantive image) such as a still life or person photographed in the color film original. That's exactly what I did.

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 formula, it is assumed that the gradation characteristic curve for the 0th plate, which is the standard among multicolor plate making, is set, so the sensitivity characteristic curve of the R emulsion layer of the color film is shown in Figure 1. (Photographic density characteristic curve) is shown. Therefore, for other color versions (M version, M version), G, B
It goes without saying that the sensitivity characteristic curve (photographic density characteristic curve) of the emulsion layer can also be used.

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

For example, vertical axis = D ==logIO/I, horizontal axis =
X (however, the scale of the X-axis is made to match the D-axis), and if a, b, c, de, and f are constants, then (A region where the D value is small in a convex shape) D: a, bc (X+d) 10+f (A region where the D value is an intermediate value in a substantially straight line CIl) D=a- x 10 b or D = a - X2 + b
() Dcl 7 + d, etc. may be used.

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.

(Table 1) Numerical formula for photographic 1 degree characteristic curve - table In the present invention, as shown in FIG. 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 logE of the image (image) 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 shows the logarithm of the exposure amount E (Hog E == log I xt)
is positioned, and this corresponds to the fact that the visual discrimination characteristic of brightness and darkness is evaluated logarithmically and is linear (linearity, linear).From the above points, the scaling of the D axis and the X axis described above. I think that the relativization (simulation) of making them 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 is not based on the density information value (Dn value) expressed by the D value of each pixel of the object (substantive image), but rather on the image information value (Dn value) correlated to the amount of light expressed on the X axis. Xn value). The photographic density characteristic curves are shown in Table 1. Value and X.

Since the value is correlated by the formula between X = f (D), it is easy to understand. The X0 value can be determined from the value.

As described above, the image information value (Xn value) correlated to the amount of light incident on the photosensitive emulsion layer from the subject (substantive image)
can be easily obtained.

Next, the Xn value at each pixel of the document image (medium image) reasonably determined in this way is calculated using the above-mentioned 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
The Xn value and the corresponding y are displayed in the orthogonal coordinate system of the vertical axis
As mentioned above, when the values are plotted, a gradation characteristic curve can be obtained. In order to distinguish the present invention from the prior art, the gradation characteristic curve will be referred to as an
A curve that emphasizes the density information value on the axis is called a D-axis combination/decomposition curve.

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

(gradation conversion formula (1)) of the present invention under certain conditions, that is, Q
, yH,3's, and γ values are respectively operated as constant,
Using multiple original images that have different image quality (that is, each original has different density ranges and density information values), create an X-axis combination and decomposition curve (gradation characteristic curve) for each original image.
When calculating, each X-axis combination/decomposition curve (gradation characteristic curve) obtained is a relative representation of all the arrangement states of y values from the H section to the S section of the final product (reproduction image C, for example, a printed image). It has the characteristic of having the same relationship. This is a very important feature of the invention. In other words, as shown in the examples described later, even if the range of image information values (y values) correlated to the light intensity on the X axis of each original image is different (this is due to the image quality of the original image). (This reflects the difference and is natural if the density range is different.) When adjusted to the same predetermined X-axis range, the X-axis combination/decomposition curve (gradation characteristic curve) obtained by the present invention It means converging on (the only thing).

Therefore, from each X-axis angular resolution curve (c gradation characteristic curve), for example, the arrangement state of halftone dots (when the y value corresponds to the halftone dot area % value), what kind of image quality will the final replicated image have? However, it is possible to accurately evaluate in advance without making proofs.

On the other hand, D! In the color separation curve, curves corresponding to each original image are obtained, but even if adjusted to the same D-axis range on the D-axis as described above, these curves are -
It is something that cannot be contained in a book (the only thing). In other words, each D-axis angular resolution curve merely indicates options for gradation conversion, and unless the proof is printed according to each D-axis angular resolution curve, the specified gradation conversion will be performed and a duplicate image of the desired image quality will 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 <gradation conversion formula (1)> of the present invention, it is possible to rationally In other words, the operator who manages the gradation conversion work can change the shape of the gradation characteristic curve to
〉, the gradation of the reproduced image can be adjusted (corrected, changed) as desired, in other words, the
The gradation conversion work can be managed rationally based on the alignment/decomposition curve.

Above, the features and characteristics that should be possessed by the image gradation adjustment mechanism, which is the central mechanism in the laser beam printer of the present invention, have been explained mainly using the production of printed images as an example.
There is no real difference in the way a scanner (monochrome or color) produces a printed image and the way a laser beam printer produces a reproduced image.

However, with laser beam printers, it is rare for original images to be recorded on photographic light-sensitive materials (especially negative types), and printed matter containing photographic images, color or monochrome photographs (positive), etc. These are the real objects of reproduction (substantive images), and these are recorded or accumulated in the density information reading mechanism of the printer system (recording medium system such as CCD) to form a medium image. It goes without saying that it may be anything. ),
A duplicate image is produced based on the density information values obtained from this.

As a recording medium, that is, in order to obtain density information values from an original image (substantive image), various types of devices such as CCD (two-dimensional CCD), photomultiplier, photodiode, and CCD are used.
These recording media, like photosensitive materials, form images (capture images) from original images using image information values that correlate with the amount of light incident on these recording media systems. It is. These recording media have unique density characteristic curves (photoelectric conversion characteristic curves) referred to in the present invention, so when producing a duplicate image from the medium image recorded on these recording media, the color film original Similarly, the basic light intensity value (X) is obtained using the density characteristic curve (photoelectric conversion characteristic curve), and then the gradation conversion formula (1
)> may be used to perform gradation conversion.

On the other hand, in the laser beam printer of the present invention, reproduction (
A color film original (negative type) recorded on a photographic light-sensitive material (recording medium in the present invention) can be used as an object for copying. In such a case, when determining the image information value that has a 1-correlation with the light amount from the density information value obtained from the density measurement mechanism (for example, CCD configuration) of the laser beam printer, do you use the photoelectric conversion characteristic curve of the CCD? The question is whether to use a photographic density characteristic curve, but it is sufficient to use either method to obtain image information values that are correlated with the amount of light. However, in the case of monochrome or color film originals, if we are trying to get closer to the true object of reproduction (copying), we must approach the original object of the medium image recorded on the recording medium of photographic light-sensitive material ( If you are trying to produce a copy that is closer to a real image, it is better to use a photographic density characteristic curve. This also applies when a laser beam printer is used to produce a duplicate image of an imaged object from an electronic still camera image or a TV image recorded on a recording medium (for example, one with a CCD configuration). It is better to use the characteristic curve of the recording medium on which the data is recorded.

In addition, when producing a duplicate image according to the present invention, it is possible to define the unique density characteristic curve (photoelectric conversion characteristic curve) of the recording medium such as a photodiode or CCD constituting the recording medium system described above. , an existing recording medium is sufficient, and thus a reproduced image with excellent gradation (density gradation and color tone) can be produced. That is, efforts have been made to improve the characteristics (photosensitive characteristics and photoelectric conversion characteristics) of various recording media in an attempt to produce high quality reproduction images, but when producing reproduction images according to the present invention, it is not always possible to There is no need for sophisticated or high performance of various recording media, and existing performance (characteristics) are sufficient. This is due to the gradation conversion method incorporated in the laser beam printer of the present invention, and is another feature of the present invention.

As explained above, when a duplicate image is formed by the laser beam printer of the present invention, the gradation adjustment mechanism is equipped with hardware or software that performs gradation conversion based on the above-mentioned <gradation conversion formula (1)>. By incorporating this, it is possible to obtain a duplicate image with excellent reproduction of tone as well as density gradation, or a duplicate image in which the image quality of the original image is arbitrarily corrected or changed.

In this case, it goes without saying that the y value (gradation intensity value) obtained by the calculation process of <gradation conversion formula (1)> should be made compatible with the density display method (variable dot method, constant dot method). There is no such thing.

(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 using a laser beam printer, is performed based on 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/separation curve of the present invention and the conventional D-ame color separation curve will be clarified. Next, a description will be given of a laser beam printer having a gradation adjustment mechanism section incorporating software or a method for performing gradation conversion based on <gradation conversion formula (1)> of the present invention.

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. Fujichrome)
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=loglxt) 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 manuscript image The image quality of the color film manuscript (medium image) can be either standard (appropriate exposure) or non-standard (over/under exposure) depending on the exposure conditions at the time of photography. There are a wide variety of such things. In order to verify whether the present invention can be rationally applied to these diverse color film originals, we investigated the density range (Dens) of color film originals.
Experiments were conducted on samples with different ity Range=DR) (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 D0 value on the D axis of various color film originals is expressed as x on the X axis.
Converted to n value. Then, the X. The value is 〈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=Xn-XHll yH=5%, ys=95%.

y=1.00. β =10-'Y =0.1.
(2 = 1.00 = γ/X, .-X Hn+ (In the case of Table 2 ■ below, X H, = 0.4781X
s n = 2, 2300. In other cases, the second
See table. ) 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 (large originals)
, respectively.

(Left below) (Table 2) Data for setting the X-axis angular resolution curve for pale color originals (Part 1) <Table 2> Data for setting the X-axis angular resolution curve for color originals with close to proper exposure (Part 2) ) <Table 2> Data for setting the X-axis angular resolution curve for dark color originals (part 3) 4. The data of the X-axis angular resolution curve Table 2 are shown in FIGS. 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, a numerical value (2.5000 in this example) was used that was adjusted as a range regarding the same light amount and density in order to create a comparison toilet room. The values after this adjustment are shown in Table 2 as (Dn-) D,' , (X,-)
Denoted as X'. Adjustment to D, -IDn' is only necessary in the case of Table 2 (■). Similarly X. -Xn' can be calculated as follows.

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

As is clear from FIGS. 2 and 3, an extremely surprising fact can be discovered. In other words, no matter what image quality a color film original is used, the tone conversion formula (1)
〉 inside α, 37H.

It is a surprising fact that when the four values of ys and γ values are made the same, the respective X-axis angular 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 angular 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, a worker who intends to produce a duplicate image using a laser beam printer must change the parameters in <gradation conversion formula (1)>, especially the γ value, using the X-axis angular resolution curve obtained as described above. The shape can be changed to a desired shape. That is, the gradation can be rationally managed so as to obtain the desired image quality and tone based on the above-mentioned X-axis angle resolution curve.

On the other hand, in the conventional color separation curve setting example shown in FIG. 3, although a D-axis angular 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 angle resolution curves. That is, under the conventional D-axis angle resolution curve, there is a drawback that it is impossible to know whether the image quality and tone of the final product are appropriate unless a proof is actually printed and evaluated.

This is a set-up process in which an appropriate color separation curve must be selected from among a large number of color separation curves in color separation work using a laser beam printer.
This also means that grooving of color originals is required in the pre-processing of set-up work. That is, the conventional technique for setting the D-axis position resolution curve cannot efficiently perform or manage the gradation conversion work.

Embodiment 2 (Laser Beam Printer) A laser beam printer of the present invention will be explained based on FIGS. 4 to 6. FIG.

FIG. 4(a) is a block diagram showing a schematic configuration of a laser beam printer of the present invention.

The image information detection unit (S) is a photomultiplier or a solid-state image sensor (
The image reading mechanism includes an image reading mechanism such as a CCD (CCD), where copies (printed matter, etc.) are recorded or stored, and density information values (Dn) are first obtained as image information of the object to be copied. Next, the image information detection unit (S) uses the density information value (Dn), for example, the photoelectric conversion characteristic curve of the CCD, to obtain an image information value (X,) correlated to the light amount, and further, a basic light amount value (X). Obtain =X, -Ln+. Note that the function to obtain the image information value (X, ) correlated to the light amount from the density information value (Dn) may be incorporated into the image processing unit (20), which will be described next. .

The image processing unit (20) uses the gradation conversion formula (1) of the present invention
A gradation adjustment mechanism with an algorithm is built in, and the rest is based on existing ones such as a shading correction circuit, γ
It is composed of a correction circuit, a masking processing circuit, a LICR processing circuit, a dither processing circuit, a multi-value processing circuit, etc.

If the original image is in color, Y, M, C.

For each of K, the gradation conversion formula (1) is applied to output a dot pattern as shown in FIG. 2B, which corresponds to each halftone based on the well-known dither matrix method.

That is, the image information signal obtained from the image information detection section (S) is gradation-converted by the gradation conversion formula (1) of the image processing section (20), and converted into a beam emitted from the laser tube (L). A recorded image with good gradation reproducibility is developed on recording paper through a photosensitive drum and a transfer drum using well-known electrophotographic techniques.

FIG. 5 is a block diagram of a laser beam printer according to a first embodiment of the present invention. As the image signal, one obtained by photoelectric scanning is used.

As shown in FIG. 5, the laser beam printer of the present invention converts the transmitted light or reflected light of the original image 5 (corresponding to the real image in the present invention) into R (red).
, G (Tarino), and B (Blue) and read the output signal from the detection unit 1 as Y (Yellow).

The color separation unit 2 converts into color separation signals of M (magenta), C (cyan), and K (black), and the color separation signal is converted into an appropriate color using the above-mentioned gradation conversion formula (I) of the present invention. A gradation adjustment section 3 performs processing to form a gradation image, and a laser beam modulated based on the output signal of this gradation adjustment section 3 exposes a photosensitive drum to form a latent image, which is then developed and output for fixing. It consists of four blocks: section 4.

Here, the detection unit 1 includes a photomultiplier or a solid-state image sensor (CCD).
) detects transmitted light or reflected light from each part of the original 5 to obtain an image information signal correlated to the density from the original 5. That is, R, G as current values,
B, USM signals are output, and these signals are converted to A/V converter 6.
It is converted into a voltage signal at

In the log amplifier 7, the color separation unit 2 has R,
The voltage signals of G, B, and LISM are converted into density by logarithmic operation, and the black (K) component is separated from this density in basic masking (BM) 8, and then the Y,
Separate the M and C components. At this time, for example, CCD
The density information value (D7) is converted into image information (i(X,)) correlated to the amount of light using the photoelectric conversion characteristic curve.

From now on, the image information value (X,) correlated to the amount of light will be used. Next, in the color correction (CC) section 9, the Y component 9 component and C component are controlled for each original color of R, G, B, Y, M, C, and the black component of the document is further controlled in the UCR/UCA section 1o. U CRfunde
r color removal + Mataba U C
A (in under color addition, the ratio expressed by three types of ink, Y, M, and C, and K (
Determine the ratio to be expressed using black ink). These Y
, M, C, and then Y,
ye, mece indicating the pixel density value in the pixel block of each color component from M, C, K, that is, the effective area ratio of each color component.
, ke'. Gradation N adjusted product 11 is <
It has the algorithm of gradation conversion formula (1)〉 inside, and Y,
Apply <gradation conversion formula (1)> to M, C, and obtain the above-mentioned ye, me, and ceke'.

The gradation adjustment unit 11 has the algorithm of ``gradation conversion formula (I)'' as software, and has A/D, D/
A general-purpose computer with an I/F (interface) of A, an electric circuit that embodies the algorithm as logic using a general-purpose IC, an electric circuit that includes a ROM that stores the calculation results of the algorithm, a PAL that embodies the algorithm as internal logic, and gates. It can take various forms such as an array, a custom 10, etc.

The effective area ratio corresponding to the color density information of each color component obtained by the gradation adjustment section 11 is determined by the color channel selector 12.
and the color channel selector 12 selects ye.
, me , ce , and ke'. This output is A/D converted by an A/D converter I3 and inputted to a dot control section 4. Thereafter, modulated laser light is emitted by the laser light source 15 according to the output of the dot control section, and an electrostatic latent image is formed on the photosensitive drum. Thereafter, the images formed by the developing machines 16a and 16b for each color are developed on the recording paper 17, and then the fixing machine 1
8. Note that 19 is a charging machine for uniformly charging the photosensitive drum.

FIG. 6 is a block diagram of a laser beam printer according to a second embodiment of the present invention. The image information signal 10' obtained from the image information detection section (not shown) (this is a density information signal of the original converted into an image information signal correlated to the amount of light) is converted into a gradation conversion formula ( 1) Adjustment section II' having
The signals are input to the optical system 1a-1b for each color through the color channel selector 12'. The laser beam modulated based on the signal outputted from the laser beam forms an electrostatic latent image having a halftone corresponding to the image information signal on each photosensitive drum 2a' to 2d', and the latent image is an electrophotographic image. The image is transferred as a color image onto the recording paper on the conveyor belt 7' by printing.

[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 an original image such as a continuous tone image and the reproduced image (image recorded by pixel distribution). 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 an irrational method based on a limited number of stator data. . On the other hand, in the present invention, no matter how many cases there are, it can be determined rationally based on the gradation conversion formula (1). 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. In other words, a laser beam printer that incorporates the algorithm of <gradation conversion formula (1)> of the present invention in its gradation adjustment mechanism theoretically and rationally systematizes gradation conversion work (color separation work). 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 a laser beam printer, the laser beam printer can be rationalized and simplified, and manufacturing costs can be reduced. In addition, operations have been simplified and clarified, greatly reducing the need for rework.
The consumption of consumable materials can be greatly saved and the performance of the laser beam printer can be greatly improved. In particular, in terms of performance, laser beam printers have the great advantage of being able to form duplicate images with excellent gradations and color tones, regardless of the quality of the original image.

3) A gradation adjustment mechanism that incorporates the algorithm of ``gradation conversion formula (I)'' 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.

By adopting the gradation conversion formula (1)), the education and training of engineers, which is currently required as image creation equipment such as printers and copiers become more sophisticated, can be improved by adopting the gradation conversion formula (1).
1)> can be carried out effectively, and it is possible to save unnecessary effort in daily work and secure time for new creative development.

[Brief explanation of drawings]

FIG. 1 shows a photographic density characteristic curve of a color film. FIG. 2 shows an X-axis color separation 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 combination/decomposition curve (used in the conventional gradation conversion) set based on the density characteristic curve of FIG. 1. FIG. 4(a) is a block diagram showing a schematic configuration of a laser beam printer of the present invention, and FIG. 4(b) is an explanatory diagram of a dither matrix. FIG. 5 is a block diagram of a laser beam printer according to a first embodiment of the present invention. FIG. 6 is a block diagram of a laser beam printer according to a second embodiment. 1 diagram

Claims (1)

[Claims] 1. The density information value of each pixel of the original image is obtained from the medium image recorded on a predetermined recording medium, the density information value is processed by a gradation adjustment mechanism, and the density information value is processed based on the processed signal. In a laser beam printer for forming a reproduced image having halftones of one color or multiple colors on recording paper, the gradation adjustment mechanism (i) determines the density information value (D_n value) of each pixel of the original image; )of,
Each pixel is determined by using a density characteristic curve that defines the relationship between the density information value (D value) of the recording medium and the image information value (X value) correlated to the amount of light incident on the recording medium from the original image. Convert the density information value (D_n value) of A laser beam printer characterized by converting into a gradation intensity value (y value) for gradation adjustment according to formula (1). <Gradation conversion formula (1)> y=y_H+{α(1-10^-^k^X)}/{α-
β}(y_S−y_H) [However, the above gradation conversion formula (1
)>, X: (X_n−X_H_n) is shown. This is calculated from the image information value (X_n) correlated to the light amount of the corresponding pixel obtained from the density information value (D_n value) of an arbitrary pixel on the original image using the density 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 through the density characteristic curve from the density information value (D_H_n) of the bright 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 recording paper for forming a duplicate image. β: Numerical value determined by β=10^-^γ. K: γ/(X_S_n - X_H_n) However, X_S_n is 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 density characteristic curve. Image information value (X_
S_n). γ: arbitrary coefficient. respectively. 2. For recording pixels on a recording sheet, a latent image representing the distribution of the pixels is formed by scanning a laser beam on an image forming member having a uniformly charged photoconductive layer, and the latent image is 2. A laser beam printer according to claim 1, wherein the image is developed with toner, transferred to a recording sheet, and further fixed. 3. The laser beam printer according to claim 1, wherein the medium image is recorded on a photoelectric conversion element as a recording medium. 4. The density characteristic curve of the recording medium is a photoelectric conversion characteristic curve that defines the relationship between the density information value (D value) and the image information value (X value) correlated to the amount of light incident on the recording medium from the original image. The laser beam printer according to item 3. 5. The laser beam printer according to claim 1, wherein the medium image is recorded on a photographic material as a recording medium. 6. A claim that the density characteristic curve of the recording medium is a photographic density characteristic curve that defines the relationship between the density information value (D value) and the image information value (X value) correlated to the amount of light incident on the recording medium from the original image. The laser beam printer according to item 5.