JPH0413372A - Method and apparatus for picture processing and transmission - Google Patents

Abstract

PURPOSE:To improve the reproducibility of density and gradation by acquiring a picture information of an original picture to be copied being a true object and processing the picture information with a specific gradation conversion equation so as to obtain gradation intensity. CONSTITUTION:A sender side equipment A reads an original picture with a detector 2 by photoelectric scanning or the like and a correction processing section 3 applies required processing such as shading correction. Then a gradation adjustment section 4 decides an area ratio of a picture element recorded on a recording sheet corresponding to the density of an original picture according to (gradation conversion equation I). Moreover, a compression section 5 applies compression processing to picture information to eliminate the redundancy of the picture information in the case of sending a picture information signal obtained by the gradation adjustment section 4. Then a modulation section 6 modulates the on the other hand, into a carrier signal and the signal is sent through a line or a data network or the like. In the gradation conversion equation I, x is a basic luminous quaintly, y is a gradation intensity set to a picture element on a copied picture corresponding to an optional picture element on an original picture, yH and yS are preset gradation intensity values at brightest and darkest parts on the original picture, alpha is a surface reflectance of a copied medium, betais a numeral decided by beta=10<-gamma> and k, gamma are constants.

Description

[Detailed Description of the Invention] [Objective of the Invention 1 (Field of Industrial Application) The present invention provides a new gradation conversion method for converting image information signals obtained from original images in facsimiles and the like that process and transmit image signals. The present invention relates to a method and an apparatus for forming a duplicate image with excellent gradation reproducibility based on the gradation-converted output signal.

Specifically, the present invention covers various original images (the present invention includes all those to be reproduced on various media such as recording paper and CRT). , When trying to create a duplicate image from an original in the usual sense, such as a monochrome or color photographic image or a video signal (TV) image, not only these images themselves become the original image, but also the original scenery, When forming a duplicate image from a subject such as a still life or a person, or the object itself (in other words, the original image is sometimes referred to as an original image), it is important to obtain the true image information value from the original image. This is converted using a gradation adjustment mechanism using a new gradation conversion formula, and then sent. Based on this gradation-converted output signal, the receiving side adjusts the gradation and color reproducibility. The present invention relates to a method and apparatus for processing and transmitting images that can produce superior reproduction images.

More specifically, the present invention provides image processing, transmission, and apparatus for forming a duplicate image from an original image by inputting image information values to various image information input media (for example, a photosensitive material or a two-dimensional CCD). Photoelectric conversion elements such as photodiodes, photodiodes, and CCDs are used.

), but (in the present invention, in comparison with the original image, the images on these input media are collectively referred to as medium images. Note that the four original images are not recorded or accumulated using manual media). It also covers cases in which the image information values are simply processed to obtain the image information values without being processed), density information values obtained from the media image (this should be interpreted in the broadest sense as described below). ), instead of using image information values that are correlated to the amount of light input to these input media in order to form a media image from a document image, such image information values are converted into a new gradation transformation. It is an object of the present invention to provide image processing and transmission, and an apparatus thereof, which has a gradation adjustment mechanism that performs conversion processing based on the formula.

(Prior art) When duplicating an image from an original image with continuous gradation such as a photograph, if photosensitive paper is used as a recording sheet, analog processing (exposure) of the original will produce an image with continuous gradation corresponding to the original. is formed (silver halide photographic record). on the other hand,
Various printers that digitally record images on plain paper,
Copying equipment, etc., does not form images using the analog processing described above, so it is difficult to reproduce density gradations (gradations).Especially in the case of duplicating color images, it is difficult to reproduce tone (color balance) in addition to the density gradations described above. )
Adjustment is also not easy.

For this reason, efforts are being actively made to improve the reproducibility of gradation and color tone in image forming apparatuses for forming various types of reproduced images. The formation of a duplicate image in an image forming device, such as a copying machine, involves photoelectric scanning of an original image with continuous gradation such as a photograph, similar to the method of converting continuous gradation to halftone gradation in photolithography in printing. The density information values obtained are processed, and the signals are used to form on recording paper an image consisting of a pixel distribution having gradation and color tone corresponding to the original image.

However, current image forming apparatuses such as copying machines and printers, as well as devices for transmitting and restoring image information signals to form duplicate images, which are the object of the present invention, do not utilize density information values obtained from original images. The gradation adjustment method for reproducing the density gradation is unscientific, so it is not possible to obtain satisfactory density gradation and the reproducibility of the color tone that is closely related to it. This is the current situation.

As is well known, the density gradation of a duplicate image depends on the pixel density display method in the image forming apparatus.

Methods for displaying such pixel density gradations include changing the pixel coverage rate by changing the size of the dot (size modulation method), and changing the pixel coverage rate by changing the number of arranged dots (of the same size). There are two methods: (density modulation method), a method (density modulation method) that changes the density of the dots themselves (of the same size), and a method that changes the brightness of pixels as seen in CRT displays, liquid crystal displays, etc.

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 pixel coverage rate (ratio of dots to the number of unit pixels that make up the pixel block), that is, the density gradation of the pixel, is determined by the diameter and density of the dots. The value below the specified value C is called the gradation intensity value of the pixel or simply the gradation intensity value.

This term is commonly used in the various pixel density gradation display methods described above. ), and how to obtain such a gradation intensity value for 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 image quality that the equipment manufacturer did not expect, such as non-standard originals (over-bright originals with N light overflow).
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 a duplicate image is finally formed based on the 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, when forming a duplicate image using various image forming apparatuses such as copying machines, as well as image forming apparatuses that involve the transmission and restoration of image information signals, which is the object of the present invention, it is necessary to A conventional method uses an image information detection (reading) mechanism of the image forming apparatus, more specifically, an image information value obtained from a medium image recorded or stored on a recording medium such as a CCD, as the image information value. Instead, the image information values of the object (original image) that is the true object of reproduction are obtained, and the image information values obtained in this way are processed with a specific tone conversion formula to change the tone. It has been found that when determining intensity values, reproduced images 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 image information signal is reproduced in a recording medium system that constitutes an image information acquisition mechanism of an image forming apparatus, such as a facsimile, which involves the transmission and restoration of image information signals. Before and after an object is recorded, stored, or processed in a recording medium system,
The object that is truly the object of fil reproduction is called the original image or real image that is 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) (ii ) The things recorded or stored in the recording medium system,
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 manually obtained from the medium image (this can be any physical quantity correlated to the density as described later). ), but rather the relationship between the density information value of each recording medium and the image information value that correlates with the amount of light from the original image incident on the recording medium. Specifying characteristic curve (
Hereinafter, in the present invention, the above-described characteristic curve of each recording medium system will be collectively referred to as the density characteristic curve, regardless of the recording medium system. ) is an image information value correlated to the amount of light obtained through According to the present invention, when converting the image information values correlated to the light amount using a specific <gradation conversion formula> to obtain gradation intensity values for gradation conversion, an image faithful to the original image (substantive image) is obtained. It is possible to obtain a duplicate image in which not only the characteristics but also the image characteristics are arbitrarily modified or changed.

In the present invention, as described above, the original image (substantive image)
refers to the image that is the true object of reproduction, and does not refer to media images recorded or stored on various recording media or processed on the recording media. It is literally the original manuscript that forms the basis of these media images. In addition, in the present invention, when a transparent color film original is used as an object to be reproduced, as will be described later, actual scenes such as landscapes, still lifes, and people recorded on the film (recording medium called photographic light-sensitive material) can be used. (In photographic images, etc., this is called the subject.) may be the true object of reproduction. In such a case, the subject becomes the original image. In the present invention, these are collectively referred to as original images (substantive images).

The present invention improves the conventional reproduction image production technology that emphasizes the density information value obtained from media images on various recording media, and improves the original image (substantive image) that is the true target of reproduction. Incorporating a completely new reproduction image production technology that emphasizes the image information value that the original image has, 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 purpose of this project is to provide image processing and transmission, as well as a device for the same.

[Structure 1 of the Invention (Means for Solving the Problems) To summarize the present invention, the present invention particularly includes processing an image information signal obtained by photoelectrically scanning an original image on the transmitting side with a gradation adjustment mechanism, The processed signal is subjected to processing such as compression and modulation processing for transmission, and then transmitted.The receiving side modulates and restores the received signal to form an image information signal, and based on this signal, a copy image is formed. The present invention relates to image processing and transmission, such as a facsimile machine, for forming a duplicate image with excellent gradation reproducibility of an original image on a medium, and an apparatus therefor. That is, in the present invention, on the transmitting side, the density information value of each pixel of the original image is obtained from the medium image where the original image is on a predetermined recording medium, and the density information value is processed by the gradation adjustment mechanism. Then, the processed signal is compressed, modulated, and transmitted, and the received signal is demodulated and restored on the receiving side. Based on the output signal, a duplicate image is formed. Image processing and transmission are performed. In the method, the gradation adjustment mechanism adjusts the density information value (Dn, value) of each pixel of the original document image,
The density information value (D value) of the recording medium and the image information value (X
(a) Using the concentration characteristic curve that defines the relationship between
converting the density information value (Dn value) of each pixel into an image information value (Xn value) correlated to the light amount;
The present invention relates to image processing, transmission, and an apparatus thereof, characterized by converting the gradation intensity value (y value) into a gradation intensity value (y value) for gradation adjustment using the following <gradation conversion formula (1)>.

<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 applied to 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. Therefore, much of the explanation will be given in relation to techniques for producing printed images using scanners (monochrome and color scanners). However, this is for convenience of explanation, and since similar problems exist in image processing and transmission in facsimiles, etc., which are the subject of the present invention, and in gradation conversion in such devices, we will not discuss them here. The value of the described tone transformation theory of the present invention is not in any way diminished when it is built into these image processing and transmission and apparatuses.

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 (co
Prior to improving color correction (correction) technology, we believe that technology that can rationally convert the density gradation of each pixel of an image must be prioritized. There is.

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. 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 from the original image (substantive image), the original image is first recorded or stored in the recording medium system of a device for producing a duplicate image (in other words, it is not considered as a media image), and from there the original image is manually recorded. This means that the gradation conversion of the image is performed using the density information value as a clue. This depends on the photosensitive characteristics and photoelectric conversion characteristics of the recording medium system, and does not mean that the image information 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 detecting the density information value from a color film original (medium image) and using it for image gradation conversion, it is not based on the image information of the subject (substantive image). In conventional technology for producing printed images using color film originals (media images), light incident from the subject onto the photographic light-sensitive material (photosensitive emulsion layer), which is the recording medium, is controlled under predetermined exposure conditions (well-known Under the conditions of incident light intensity ■ and incident time t, the exposure amount E is expressed as E=It.) Color separation work (color separation work and includes both the color correction and gradation control described above.

As is well known, photographic light-sensitive materials on which subjects have been photographed have a photographic density (photographic density) that is obtained by 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 (ph
otographic characteristic
It is a curve. This shows the photographic density (Di) on the vertical axis.
fD = log Io/I), and the logarithm value (logE) of the exposure amount E is plotted on the horizontal axis. In addition, for films and dry plates (transparent originals), the ratio between the intensity of transmitted light and the intensity of incident light is IO, and for photographic paper (reflective originals), the ratio is the intensity of reflected light I and the intensity of completely reflected light Io. It goes without saying that the ratio of

A typical photographic density characteristic curve is a fairly complex curve with a downwardly convex foot, an approximately straight line, and an upwardly convex shoulder (for this point, please refer to 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, since the absolute value of the exposure amount may be used or the relative value may be used as described later, this will be referred to as "image information value correlated to the light amount"), That is, it is not a color separation technique constructed from the standpoint of the horizontal axis of the photographic density characteristic curve (image information value correlated to the amount of light). The density information value of a color film original, which is the basis of the color separation work in the prior art, is different from the image information value which correlates with the light intensity 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). cannot be correlated with a linear relationship (1:1 45° linear relationship).

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

Therefore, in producing a color printed image, the density value (D=log IO/
If you proceed with the work using I) as a clue, you will be using the density information value after being influenced by the photosensitive characteristics of the photosensitive flower material for photography, and it will be possible to use the density information value after being influenced by the photosensitive characteristics of the photosensitive flower material for photography. This does not mean that image information values correlated with 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 first image from the original image (substantive image, subject) that is the true target of reproduction is obtained without using the density information value of the medium image that is affected by the photosensitive characteristics and photoelectric conversion characteristics of photoelectric conversion elements (photoelectric conversion elements such as CCDs). We conducted extensive research on methods for producing various types of replicated images based on image information values that correlate with the (raw, primitive) amount of light.

As a result, in the production of printed images, (1) using the photographic density characteristic curve, the vertical axis (D=log
The value of the horizontal axis (logE) is calculated from the value of IO/T (hereinafter, the vertical axis is also referred to as the D axis, and the horizontal axis is also referred to as the X axis), in other words, the brightest value specified on the photographic density characteristic curve. The image information value (X value) on the X axis is calculated by projecting the density information value (D value) on the D axis of the color film original (medium image) from the darkest part to the darkest part on the X axis, (2) More specifically, the density value (Dn value) of an arbitrary pixel on the medium image on the D axis is projected onto the X axis via the photographic density characteristic curve to calculate the image information value (Xn value) of the corresponding pixel. (X
In the photographic density characteristic curve, the axis indicates the logarithmic value of the exposure amount, but in the present invention, its absolute value may be used 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 called 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) X obtained as described above. Based on the x7 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 x7 value, and thereby the halftone We have discovered that when the size is controlled, a printed image with excellent halftone gradation and image characteristics faithful to the subject (substantive image) can be obtained.

In the image gradation conversion of the present invention, when converting the density information value of an arbitrary pixel on the original image into the gradation intensity value of the corresponding pixel of the duplicate image, various types of density information values as described above are used as the density information value of the pixel. Density information values obtained from a medium image recorded or stored on a recording medium are not used as they are. In other words, the image information value of the original image (substantive image) 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 input from the original image to various recording media). The major feature of this method is that it calculates the image information value (correlated to the amount of light) and processes it using the above-mentioned gradation conversion formula (1) to convert it into a gradation intensity value. be.

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.)
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 producing a duplicate image with a significantly large gradation and excellent gradation reproducibility. and,
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 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 for overcoming these complicated and unstable factors be built into the image forming apparatus.

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 area (H) on the duplicate image is and the gradation intensity value (y6) 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. 63114599), the operating conditions thereof are completely different from those of the present invention.

<Tone conversion formula> for calculating the numerical value (y) of the halftone area percentage used when producing a printed image with the halftone gradation proposed above (As mentioned above, the basic framework of this is the present invention) This is similar to the gradation conversion formula (1), but
The operating conditions are completely different. ) can be derived from generally accepted density formulas (photographic density, optical density). That is, it can be derived by applying D=log 0/I=logl/T.

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

Guaru・Shikono plate making・
In the density formula (D') related to printing, it is possible to arbitrarily set halftone dots of desired size on the H and 8 parts of the printed image, and also to set arbitrary halftone dots on the continuous tone image (original image). The request is to reasonably relate the basic density value (x) at a sample point and the value (y) of the halftone area percentage of the halftone dot at the corresponding sample point on the halftone gradation image (printed image). The result obtained by adaptively matching the theoretical value and the measured value is shown by the formula below (gradation conversion formula (2)).
> is.

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

yH9: While arbitrarily selecting Js and γ values, calculate the value (y) of the halftone dot area percentage of the halftone dot 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 seek. This not only allows the density gradation of the original image (continuous gradation image) to be faithfully reproduced on the printed image (halftone gradation image) with 1=1, but also
Printed images of desired image quality (having desired density gradation and color tone) can be produced.

In addition, multicolor printing (-grain 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) ) is determined, the halftone characteristic curves for other color plates can be created by multiplying the y value of the standard plate by an appropriate adjustment value based on the gray balance ratio of each printing ink color. Therefore, decisions can always be made rationally. 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. 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 printers, copying machines, etc.

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 in the <gradation conversion formula (l)> of the present invention, 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) must be determined from the medium image in which the original image is recorded on a predetermined recording medium. As mentioned above, the basic light amount value (x) is determined by the original image −F via the density characteristic curve of the recording medium on which the original image is recorded or stored.
This is determined using the density information value (Dn value) of a predetermined pixel as a clue.

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 270 on the vertical axis, and the corresponding value on the horizontal axis is adopted.)
+ [gradation intensity value set for the brightest (H) pixel] and 3
/s If a percentage value (for example, 5% or 95% pixel coverage) is used for [gradation intensity value set for the darkest (S) pixel], the y value [any pixel on the original image] [gradation intensity value set for a pixel on the duplicate image corresponding to] 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.

X y=yH1E (1-10N ys -yH) In the above modification, α=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 of the density measurement mechanism is adjusted using the recording paper as a reference. Also, if the duplicate image is C
When the display is reproduced with brightness, such as on an RT display or a liquid crystal display, α:11 ports may be used in the same manner.

Further, according to the modification (α=1.0), it is possible to set 37H for the brightest part H and ys for the darkest part S on the duplicated image by the image forming apparatus as planned. this is,
In the brightest part H on the duplicate image, x = O, and in the darkest part S, x = [X sn
], that is, -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−γ as described above) take various values. In the present invention, by appropriately selecting these values, it is possible to rationally perform image gradation conversion processing regardless of the quality characteristics of the original image.

That is, the image gradation conversion processing method based on the above-mentioned (Pa tone conversion formula (J)) 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. The above-mentioned gradation conversion formula (1) of the present invention faithfully reproduces the characteristics of the original image. In addition, the characteristics of the original image can be rationally changed by appropriately selecting the α, β, γ values, and even the yH+'ls value so that it can be easily understood from the nature of the gradation conversion formula (1). Of the parameters in gradation conversion formula (1), the γ value is particularly useful for adjusting (including correction or change) the characteristics of the original image. What plays a major role in this is the gradation conversion formula (1)
It is easy to understand if you try to use it.

When forming a multicolor image using the above-mentioned gradation conversion formula (I), for example, when producing a color reproduction image using a color film original, a color separation technique well known in fields such as printing, i.e. , the reflected light from a color document is separated into blue (B), green (G), and red (R) to obtain a signal that correlates to the density information value (β value) for each color, and this is correlated to the light amount. Convert to image information value (y value),
Further, the image may be formed by processing with a gradation adjustment mechanism using the above-mentioned gradation conversion formula (l), and adjusting the recording unit of the image forming apparatus based on this processing information value (y value). . At that time, calculate the y value for the standard color plate (for example, 0 plate), that is, the gradation characteristic curve (y (a) of the standard color plate, and plot the y value against the y value as described above. A gradation characteristic curve similar to the halftone gradation characteristic curve in printing technology can be obtained.), and the W3 tone characteristic curve of other color plates (M plate, Y plate) is determined by the y value of the standard color plate. This can be reasonably determined by multiplying the gray balance ratio of each ink by an appropriate adjustment value, so 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, using the density characteristic curve of each recording medium, the density information value (β value) of an arbitrary pixel on the original image is determined, and the image information value correlated to the amount of light of the corresponding pixel incident on each recording medium is calculated. Next, the method for determining the (y value) will be explained.

In the present invention, in order to obtain image information values, particularly density information values, for gradation conversion from a document image (substantive image),
The original image is recorded on various recording media, such as photosensitive material, two-dimensional CCD, photomulti, photodiode, etc.
The image is recorded on a recording medium called a photoelectric conversion element such as a CCD and becomes a medium image. Then, from the density information value (β value) at each pixel of the original image, the unique density characteristic curve of each recording medium (from the density information value read from the recording medium of the original image and the original image incident on each recording medium) The image information value (X value) correlated to the light amount of the corresponding pixel must be determined through a characteristic curve that defines the relationship between the image information value and the light amount of the corresponding pixel. For this purpose, the density characteristic curve of each recording medium must be accurately or adaptively converted into a function (formula).

Here, a method for formulating a photographic density characteristic curve will be explained using, as an example, a color film original (medium image) whose recording medium is a photographic light-sensitive material, but the density characteristic curve ( The photoelectric conversion characteristic curve) may be expressed in a similar manner. As mentioned above, when using a color film original (medium image), the true object of reproduction (original image) is the object (substantive image) such as a still life or person photographed on the color film. That's right.

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, Y version), G, B
It goes without saying that the sensitivity characteristic curve (photographic density characteristic curve) of the emulsion layer can be utilized.

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

For example, the vertical axis = D = log'' / I, the horizontal axis = X (however, the scale of the X axis was made to match the D axis), and a, b, c, d.

If e and f are constants, (a) Foot part of the photographic density characteristic curve (a region with a downwardly convex shape and a small D value) D: a, bc・(x+d)+e+f (b) Approximately straight line (A region where the D value is an intermediate value in a substantially straight line) D=a −X+b or D=a−x2+bX+c (c) Shoulder portion (A region where the D value is large in an upwardly convex shape) D= It can be expressed mathematically as a・log(b+(X+cl)+d).

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.

(Left below) <Table 1> Functional formula of photographic density characteristic curve - list, 4F? , 9Q completed, 7. ;, 'A: Can April KA)"-
CHHOME) (7) Photographic 1 degree characteristics In the present invention,
As shown in Fig. 1, the D-axis scale indicating the density value of the color film original (media image) and the X-axis scale indicating the image information value indicated by part gE of the subject (substantive image) are the same. The correlation between D and X was expressed as a function.

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 logarithm of the exposure amount E (log E = log I In view of the above points, I believe that the relativization (fiction) of making the scaling of the D-axis and the X-axis the same as described above 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 (density value) represented by the D axis of each pixel of the object (substantive image), but is based on the image information value (value) correlated to the light amount represented by the χ axis. Xn value). Then, the photographic density characteristic curve is shown in Table 1, and the value and x,
, and the value of

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, X at each pixel of the original image (medium image) reasonably determined in this way. The value is converted to the above gradation conversion formula (
I)> 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 x0 value and the corresponding y
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 the X-axis position resolution curve, and the conventional D
A method that emphasizes the density information value on the axis is called a D-axis color separation cube.

The X finely decomposed turnip obtained by the present invention described above and the conventional D
The characteristics of the axial decomposition curve will be explained.

The gradation conversion formula (1) of the present invention is set under certain conditions, that is, α
+ yo l 3'a + A plurality of color film originals (medium images) with different image qualities (that is, each original has different density ranges and density information values) are operated with a constant γ value. When determining each X-axis position resolution curve (tone characteristic curve) using a color film original, each obtained X-axis position resolution curve (tone characteristic curve)
has the characteristic that all the arrangement states of the y values from part H to part 3 of a duplicate image (for example, a printed image) that is a final product are made to have the same relative relation. This is a very important feature of the invention.

In other words, as shown in the examples described later, even if the ranges of image information values (y values) correlated to the light intensity on the X axis of each original image are different (this is true for color film originals). (This reflects the difference in image quality and is natural if the density range is different.) When adjusted to the same predetermined X-axis range, the X-axis position resolution curve (gradation characteristic curve) obtained by the present invention is -It means to converge on the book (the only thing).

Therefore, from each X-axis resolution 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 D-axis is adjusted to the same D-axis angle as described above,
These are things that do not fit into a book (the only thing). In other words, each D-axis resolution curve merely indicates options for gradation conversion, and unless a proof is printed in accordance with each D-axis resolution curve, a predetermined 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 the gradation conversion formula (1) of the present invention, by arbitrarily changing the α, :JH, ys, and γ values (particularly by changing the γ value), In other words, the operator who manages the gradation conversion work can use the gradation conversion formula (1) of the present invention.
)> The gradation of the reproduced image can be arbitrarily adjusted (corrected, changed) to the desired one, in other words, the gradation conversion work can be streamlined based on the X-axis color separation curve. can be managed effectively.

Above, we have explained the features and characteristics that the image gradation adjustment mechanism, which is the central mechanism in the production of reproduced images according to the present invention, should have, mainly using the production of printed images as an example. There is no substantial difference in the method of producing an image, the equipment involved in transmitting and restoring the image information signal, that is, the processing and transmission of the image, and the method of producing a duplicate image using the equipment.

However, in image transmission, the density information detection (reading) mechanism (consisting of a recording medium system such as a CCD) of the image transmission device from the original image does not form the medium image, and of course it is a temporary image. Needless to say, it is possible. ), converts the density information value obtained from this into an image information value correlated to the amount of light, and also uses <gradation conversion formula (1)>
The data may be processed and transmitted so as to calculate the gradation intensity value, and then restored to form a duplicate image.

There are various types of recording media of this kind, such as two-dimensional CC.
Photoelectric conversion elements such as D, photomultipliers, photodiodes, and CCDs are used, but these recording media, like photosensitive materials, convert images from original images that are correlated to the amount of light incident on these recording media systems. Image formation (image transport) based on information value
It is something to do. These recording media have unique density characteristic curves (photoelectric conversion characteristic curves) as defined in the present invention, so when producing a duplicate image from a medium image recorded on these recording media, the color As with film originals, the basic light intensity value (X) is determined using the density characteristic curve (photoelectric conversion characteristic curve), and then the gradation conversion formula (1
)> may be used to perform gradation conversion.

In addition, in the image processing and transmission such as a facsimile of the present invention, and its device, when the object of image transmission is a color film original (negative type) recorded on a photographic light-sensitive material (recording medium in the present invention) There is. In such a case, when converting the density information value obtained from the density measurement mechanism (for example, composed of a CCD) into an image information value correlated to the amount of light, do you use the photoelectric conversion characteristic curve of the CCD or do you use the photographic density? The question is whether to use a 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, the actual object of reproduction (copy) is a copy that is closer to the subject (substantive image) that is the source of the media image recorded on the recording medium of photographic light-sensitive material. If you are trying to produce a photographic density characteristic curve, it is better to use a photographic density characteristic curve.

In addition, when producing a duplicate image according to the present invention, various recording media such as photodiodes and CCDs constituting the recording medium system described above are used, and the unique density characteristic curves (photoelectric conversion characteristic curves) of these recording media are used. If it can be defined, existing recording media will suffice, and thereby a reproduced image with excellent gradation (a-degree 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 image information signal processing and transmission equipment of the present invention, and is another feature of the present invention.

As explained above, when producing a duplicate image using the image transmission and apparatus of the present invention, the gradation adjustment mechanism section performs gradation conversion based on the above-mentioned gradation conversion formula (1). By incorporating hardware or software, 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.

At that time, the y value (gradation intensity value) obtained by the calculation process of <gradation conversion formula (1)> is displayed using the density display method (size modulation method, density modulation method, density modulation method) suitable for each image forming apparatus. It goes without saying that it is sufficient to correspond to a display method based on brightness such as RCT or liquid crystal display.

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.

The pixel block here is of a 4×4 matrix type, and 17 levels of gradation are thereby expressed. - Matrix type pixel block of n×n numerically n”+1
Gradation levels (0 to 100%) are 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 known numerically as the dither-matrix method. (For example, JP-A-58-
No. 85434, No. 58-114569, No. 59-52
No. 969, No. 60-141585, No. 62-1866
No. 63, etc. ).

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

In the present invention, the gradation conversion of the image, which is central to image processing and transmission, and the production of a duplicate image by the device, is performed based on the gradation conversion formula (1) above. It has the greatest feature. 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, the gradation conversion formula of the present invention (1
)> An image processing and transmission system having a gradation adjustment mechanism incorporating software or an 8-bit code that performs gradation conversion based on the following will be described.

Example 1 (Setting of X-axis synthesis/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=IogIX 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) varies depending on the exposure conditions of the camera, such as standard (appropriate exposure) and non-standard (over/under exposure). ) and so on. 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=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,
D-axis upstream of various color film originals (media images). The value is X on the X axis. converted to a value. Next, the X value was converted into a gradation intensity value (y value) using the gradation conversion formula (1).

The operating conditions for <gradation conversion formula (1)> are as follows: x=Xn -XHn yH=5%, ys=9s%.

γ='1.00. β=IO-0,1,α=1.0Ok
=γ/X, h−X, n.

(In the case of Table 2 ■ below, X H, = 0.4781X
5ll=2.2300. For other cases, please refer to 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,
In Table 2, ■~[Phase] indicate unexposed light color (Table 2) Setting button for X-axis combination/resolution curve for original (Part 1) (A-colored original), respectively.

(Space below) <Table 2> Data for setting the X-axis angular separation curve for color originals with close to proper exposure (Part 2) <Table 2> Data for setting the X-axis angular separation curve for dark color originals (Part 3) ) 4. The data of X-axis angular resolution curve Table 2 is 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 making the graph, for convenience of comparison, values adjusted as ranges for the same light amount and density (2.5000 in the case of this example) were used. In the table (Dn, →) D,', (Xn-)
Denoted as x'. The adjustment to D, -10,,' is, in the case of Table 2 ■, Do' = (Dn-1,800) x
(Adjustment) Rn = I Do1', 800) x ""'i:
Yo') Calculation h2.52 Good. Similarly, x, , -xn' can be calculated as follows: 2.500 xn'=(x,, -0,4781)xl, 7519.

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, DI, ′ and y, which 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 (medium image) is used, if the four values of a+ yH+ yH+ γ values in <gradation conversion formula (1)> are made the same, then the It is a surprising fact that the respective X-axis angular separation curves converge into one and the same curve, and the tone of the color reproduction image obtained after color separation is uniformly displayed. be. In other words, according to the technology for setting the gradation characteristic curve (X-axis angular resolution curve) of the present invention, no matter what image quality color film original is used, it is possible to produce duplicate images of the same quality with the same arrangement of y values. A gradation characteristic curve that can be manufactured is obtained. In addition, an operator who intends to process and transmit an image of the present invention, and to produce a duplicate image using the device, can convert the X-axis combination and decomposition curve obtained in the above manner into the By changing the parameters, especially the γ value, the shape can be changed to a desired shape. 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 a large number of color separation curves during image processing and transmission, and tone conversion work applied to the device. This means that grooving of the color film original (media image) is required in the pre-process.In other words, the conventional D-axis integration/separation curve setting technology cannot efficiently perform or manage the gradation conversion work. I can't.

Embodiment 2 (Image processing and transmission, and its apparatus) Image processing and transmission, and its apparatus, of the present invention will be explained based on FIGS. 5 to 7.

FIG. 5 is a block diagram of an apparatus that performs image processing, transmission, and image formation on a recording sheet using the gradation adjustment method of the present invention. There are various possible devices for forming images on recording sheets on the receiving side, but here we will use an electrophotographic device that forms a latent image on a photoconductive image forming body by scanning a laser beam. There is.

The transmitting device A has a detection unit 2 that reads the original image 1 by photoelectric scanning, etc., and a correction processing unit 3 that performs necessary processing such as shading correction on the output signal of the detection unit 2, and then performs necessary processing such as shading correction. )> determines the area ratio (gradation intensity value) of pixels to be recorded on the recording sheet in accordance with the density of the original image. When transmitting the image information signal obtained by the gradation adjustment section 4, the compression section 5 performs compression processing to remove redundancy of the image information in order to improve transmission efficiency and speed. The compression processing method for images containing halftones is CCI TT's G3. MH according to G4 standard
method, MR method, etc. The compressed image information signal is modulated into a carrier signal for transmission in the modulator 6, and then transmitted via a line, data network, etc. Here, the detection unit 2 detects the transmitted light or reflected light of the original image 1 using a photomultiplier or a solid-state imaging device (COD), and converts the image information signal as a current value into a voltage signal by A/V conversion. . Further, the voltage signal is subjected to a logarithmic operation using a log amplifier and converted into a concentration information value. Next, the density information value (Dn) is
For example, by using the photoelectric conversion characteristic curve of the CCD of the recording medium system, it is converted into an image information value (Xn) correlated to the light amount and further into a basic light amount value (X).

These may be performed using software or hardware (not shown). Further, the gradation adjustment section 4 may have a function of determining an image information value (Xn) correlated to the light amount from the density information values fD, l.

In device B on the receiving side, the received signal is first modulated in the modulation section 7, and further restored to an uncompressed image information signal in the restoration section 8. An image forming unit l used to form an image on a recording sheet in the output unit 9 on the restored signal.
It is converted into an image forming signal of O.

In the case of an electrophotographic image forming method, a uniformly charged photoconductive image forming body surface is scanned with a laser beam modulated by a signal from the output section 9 to obtain a charge distribution corresponding to the image to be formed. A latent image is formed, and this latent image is developed with toner in a developing device. The toner is charged as necessary by frictional charging or the like so that it can easily adhere to the latent image. The toner image formed on the image forming surface is transferred to a recording sheet in a transfer section. Normally, in this transfer section, transfer is performed while a corona discharger discharges the toner from the back side of the recording sheet to transfer the toner to the recording sheet side. The recording sheet onto which the toner image has been transferred is transferred to a fixing section, where it is fixed by heating, pressure, etc., and image formation is completed.

This is a process in which one type of toner is used, but next, an example in which a multicolor image is formed will be explained with reference to FIG.

In FIG. 6, a color original image 1 is detected by a detection unit 2 (different from the one in FIG. 5, R, G, B).

The USM signal is detected for each color, and the output signal is processed into R and G by the processing section 3.

The B and USM component signals are color separated into Y, M, and C components, and necessary processing such as shading correction is performed. The output signal of the processing unit 3 (this is not the density information value, but
This is an image information value that correlates with the amount of light. ) is the area ratio (gradation intensity value) of the image recorded on the recording sheet that corresponds to the pixel density of each color of the original image after the gradation adjustment is performed in the gradation adjustment section 4 using the gradation conversion formula (1). is converted into a signal indicating The output signal of the gradation adjustment section 4 is compressed in a compression section 5 for transmission, modulated in a modulation section 6, and transmitted. The signal received on the receiving side B is demodulated by the demodulation section 7 and restored to the uncompressed image information signal by the restoration section 8. The restored image information signal is converted into a signal for forming an image in the image forming section 10 at the output section 9 for each color component. Based on the signals for each color from the output section 9, the image forming section 10 performs the processes of forming, developing, and transferring a latent image by scanning with a laser beam, as in the case of one color.
This process for each color is repeated as many times as the number of colors, and after alignment and transfer to the recording sheet, fixing is performed, and the image forming process is completed.

After one image formation is completed, there is toner remaining on the photoconductive image forming body without being transferred to the recording sheet, so this is removed with a cleaning blade, brush, etc., and the remaining charge is irradiated with light. Alternatively, it is removed by corona discharge to prepare for the next image formation. Removal of this toner is 1
If the toner is transferred to the recording sheet each time a color is developed, it should be done after the transfer of each color is completed, and if the image forming body is to be transferred at once after development with toner of all colors, it should be done after this one transfer. Remove remaining toner.

In FIGS. 5 and 6, the image forming section 10 has been described as an electrophotographic type that forms an electrostatic latent image on a photoconductive image forming body by scanning a laser beam, but a recorded image is formed by the distribution of pixels. As a forming method, other methods such as electrostatic recording and magnetic recording heads can be adopted.

In electrostatic recording, each electrode of a recording head has a large number of electrodes arranged in a direction perpendicular to the moving direction of the image forming body in the vicinity of or in contact with a moving image forming body made of a dielectric material in the form of a sheet or a rotating drum. 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. A voltage as an output signal corresponding to the image to be recorded is applied from the dot control section of the output section 9 to the recording head as an assembly of electrodes. In addition, in the magnetic recording type, the image forming body 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. A toner made of magnetic material is used to develop this magnetic latent image, but other processing is performed in the same manner as in the case of electrophotography. In the case of a magnetic latent image, it takes longer to form a latent image than in the case of an electrostatic latent image, but since the persistence of the formed latent image is good, it is possible to form a latent image once with one type of toner. An image is formed by developing with toner many times. Therefore, it is suitable for receiving the same original image signal of one color and forming images on multiple sheets. In the case of color images, a plurality of magnetic image forming bodies should be provided for each color, and each should be provided with a developing device or the like.

FIG. 7 shows the gradation adjustment method according to the present invention in more detail.
Detected by a photoelectric conversion element such as R, G, B as a current
, USM signals, and convert these signals into A/V converter 2.
1, it is converted into a voltage signal.

In the color separation unit 3, the voltage signals of R, G, B, and USM from the detection unit 2 are logarithmically operated in the log amplifier 31 and converted into density, and the basic masking unit (BM) 32 converts this density into gray (K). Separate the components and further Y and M.

Separate each component of C. The density information value of each color component obtained in this way, that is, the density information value for each Y, M, and C (D
n) is, for example, a CCD constituting the recording medium system of the detection unit 2.
Using the photoelectric conversion characteristic curve of , the image information value (xo) correlated to the light amount is converted into the basic light amount value (Xl).

These may be performed using software or hardware (not shown).

Further, a function of obtaining an image information value (Xo) correlated to the light amount from the density information value FD, ) may be incorporated into the gradation adjustment section 41, which will be described next.

Note that FIG. 7 shows a color correction (CC) 33 as a configuration of the color separation section 3. As shown in FIG. Here R,
The Y component and the C component are controlled for each original color of G, B, Y, M, and C, and the gray component of the original is controlled by the UCR (under co) of the UCR/UCA section 34.
ntrol re-movall, or U CA
(under control additi-anl
, the ratio expressed by the three components Y, M, and C is determined.

Conventionally, the Y, M, and C components converted into image information values correlated to the amount of light are recorded in the pixel area in the pixel block of each color component in the gradation control section in the gradation adjustment section (IMC). The ratios (gradation intensity values) ye, rIle, ce, ke' were calculated and inverse log-transformed, but in this embodiment, the adjustment section 41 is used instead of the gradation control section and the inverse-log conversion section. Here, conversion is performed from Y, M, C, and K to ye', me, ce, and ke'. The adjustment section 41 uses <gradation conversion formula (1))
It has an internal algorithm, and applies <gradation conversion formula (1)> to Y, M, and C, respectively, and ye, m
Find e, ce, and ke'.

The gradation adjustment section 41 has the algorithm of gradation conversion formula (1) as software, and has A/D, D/
A general-purpose computer with an I/F (interface) of Gert Alley, Custom I
It can take various forms such as C.

The area ratio (gradation intensity value) of pixels to be distributed in the pixel block obtained by the adjustment unit 41 is input to the color channel selector 42, and the color channel selector 42 selectively outputs ``yeme'', ``ce'', and ``ke''' sequentially. do. This output is converted to A/D by the A/D converter 43.
After being converted into D, it is input to the compression processing section 5.

This device configuration for gradation adjustment is just an example.
It is possible to make changes, omissions, simplifications, etc. as appropriate.

[Effects of the Invention] The image gradation adjustment method according to the present invention, the image processing and transmission using the method, and the apparatus related thereto have the following excellent effects.

I) The density information value of a predetermined pixel on an original image such as a continuous tone image and the gradation intensity value of the corresponding pixel on the duplicate image to be produced, which are the most basic matters in producing a duplicate image. Conventionally, determining the correlation between the two has been based solely on the experience and intuition of the operator, or on irrational methods based on a limited number of stator data. In contrast, in the present invention, no matter what the circumstances,
This can be determined rationally based on <gradation conversion formula (1)>. In addition, when converting an original image such as a continuous tone image into a duplicate image based on pixel distribution, tone management (conversion, correction, or change of tone) is the most important elemental technology.
This is not only limited to the density gradation of an image, but also has a direct and deep relationship with the tone of the image, so the present invention allows the density gradation and color tone to be managed rationally. In other words, the gradation conversion formula (1) described above for the gradation adjustment mechanism is
The image forming apparatus of the present invention, which incorporates the above algorithm, for transmitting and restoring an image information signal to form a duplicate image, theoretically and rationally systematizes the 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 an image forming device that transmits and restores image information signals to form a duplicate image, the device can be streamlined and simplified. , it is possible to reduce manufacturing costs. In addition, the operation is simplified and clear, the number of reworks is extremely reduced, the consumption of consumable materials is greatly reduced, and the performance of the device is significantly improved. Especially image processing.

In terms of transmission and the performance of the device, it has the great advantage of being able to form a duplicate image with excellent gradation and color tone, no matter what the quality of the original image is.

3) The gradation adjustment mechanism that incorporates the algorithm of ``gradation conversion formula (1)'' makes it possible to rationally and easily define evaluation standards for the quality of reproduced images, separate from the image information of the original image. . Therefore, it is possible to rationally respond to the diversified needs of customers.

4) Based on the gradation conversion formula (1), by adopting the gradation conversion method, it is possible to improve the education and training of engineers required as image processing, transmission, and related equipment become more sophisticated. <
This can be done effectively by using the gradation conversion formula (1)〉, and unnecessary labor in daily work can be saved, and time can be secured 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 angular resolution curve C (used in the gradation conversion of the present invention) set based on the photographic density characteristic curve of FIG. 1. FIG. 3 shows a D-axis decomposition curve (used in the conventional gradation conversion) set based on the density characteristic curve of FIG. 1. FIG. 4(a) shows an example where a continuous tone original image is expressed by the distribution of unit pixels within a pixel block, and FIG. 4(b) corresponds to the case of (a). FIG. 2 is a diagram showing a case where halftone dot size is expressed in photolithography. FIG. 5 is a block diagram of an apparatus that performs image processing, transmission, and recording using the gradation adjustment method of the present invention. FIG. 6 is a block diagram of an apparatus that performs image processing, transmission, and recording of a color original using the gradation adjustment method of the present invention. FIG. 7 is a block diagram showing an example of the configuration of a gradation adjustment section incorporating the gradation adjustment method of the present invention.

Claims (1)

[Claims] 1. On the transmitting side, the density information value of each pixel of the original image is obtained from a medium image in which the original image is recorded on a predetermined recording medium, and the density information value is processed by a gradation adjustment mechanism. Then, the processed signal is compressed, modulated and transmitted, and the received signal is demodulated and restored on the receiving side. Based on the output signal obtained, a duplicate image is formed.
In the method for transmission, the gradation adjustment mechanism (i) adjusts the density information value (D_n value) of each pixel of the original image;
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 method for processing and transmitting an image, characterized by converting it into a gradation intensity value (y value) for gradation adjustment according to equation (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 (Xn) 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 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 via 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 the reproduction medium for forming a reproduction 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. The method for image processing and transmission according to claim 1, wherein the medium image is recorded on a photoelectric conversion element as a recording medium. 3. Claim in which the 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. 2. The method for image processing and transmission according to 2. 4. The method for image processing and transmission according to claim 1, wherein the medium image is recorded on a photographic material as a recording medium. 5. Claim in which the 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. 4. The method for image processing and transmission described in 4. 6. A detection unit that reads the original image by photoelectric scanning or the like and converts it into an image information signal, and a pixel distribution of the duplicate image to be formed by performing correction processing on the output signal of the detection unit and further performing gradation adjustment processing. an image information transmitting side device having a processing section that determines a state, a compression processing section that applies compression processing to an output signal of the processing section, and a transmission control section that transmits after modulating the output signal of the compression processing section; A demodulation unit that receives and demodulates a signal from a transmitting side device, an output unit that restores the output signal from the demodulation unit and outputs it as an uncompressed image information signal, and a duplicate image using the signal from the output unit. and a recording image forming unit for forming a duplicate image on a copy medium for forming a copy image, and a receiving side device having a recording image forming unit for forming a copy image on a copy medium for forming a copy image. 1. An apparatus for processing and transmitting images, characterized in that the processing is performed as defined by the <gradation conversion formula (1)> described in Item 1. 7. After the replica image forming section forms a latent image representing a pixel distribution by scanning a laser beam on an image forming body having a uniformly charged photoconductive layer and develops the latent image with toner; 7. The apparatus for processing and transmitting an image according to claim 6, wherein the apparatus is adapted to transfer the image onto a recording sheet and further fix the image. 8. The replica image forming section applies a voltage to a large number of recording electrodes arranged in a direction perpendicular to the moving direction of the moving electrostatic recording type image forming body to generate an electrostatic charge on the electrostatic recording body. Claim 6: A latent image is formed, the latent image is developed with toner, and then transferred to a recording sheet and further fixed.
A device for processing and transmitting images as described in . 9. A series of operations, or a part thereof, of forming a latent image on the image forming body, developing it with toner, and transferring it to a recording sheet,
A claim in which the same operation is performed using toner of a specific color, the same operation is performed using toner of a different color, and the same operation is repeated for the required number of colors, aligned and transferred onto the same recording sheet, and then fixed. An apparatus for processing and transmitting images according to item 7 or 8. 10. The apparatus for image processing and transmission according to claim 6, wherein the duplicate image forming section is configured with a CRT display or a liquid crystal display.