KR0128707B1 - Tonal conversion method of a picture - Google Patents

Abstract

The present invention is to provide a gradation conversion method of a new image for producing a duplicate image having a gradation intensity value as designed, that is, a rational gradation conversion when reduced. In the gray scale conversion method of an image when producing a copy image of halftone gradation, the gray scale transformation of the image is (i) the density value of the sharpest part (H) and the darkest part (S) designated on the color photograph document, and H and its vicinity. Obtaining representative concentration values (DH _av , DS _av ) of S and its vicinity, (ii) Scanning each pixel point (n point) from H to S to obtain density value D _n of each pixel point (B) the density characteristic curve of the photographic material provided to the shooting of the color accident power supply specified in the DX rectangular coordinate system of the vertical axis (D axis) indicating the concentration value and the (X axis) indicating the image information value correlated with the light quantity. Representative of the above H and S Converting the density values DH _av and DS _av and the density values D _n of each pixel point into image information values X _n correlated with the amount of light, and (iii) the image information values X _n correlated with the amount of light. A step of converting the image into a tone intensity value Y using the following tone conversion equation is performed.

Gradation Conversion

y = y _H + [α · (1-10 ^−kx ) / (α-β)] · (y _s -y _H )

Description

Gradation conversion method of image

1 shows the photograph density characteristics curve of the color scattering film sensor.

FIG. 2 is a schematic diagram illustrating a dispersion state of silver particles in an emulsion layer in the aperture field of the color scanner.

3 is a schematic diagram illustrating the device configuration of a color scanner to which the tone conversion method of an image of the present invention is applied.

4 is a schematic diagram illustrating the device configuration of a digital copy machine (color copying machine) to which the tone conversion method of an image of the present invention is applied.

* Explanation of symbols for main parts of the drawings

1: detection unit, 2: color separation unit,

3: gradation adjusting unit, 4: output unit,

5: color photo document, 6: A / V converter,

7: log amplifier, 8: basic masking unit,

9: color receiving unit, 10: UCR / UCA unit,

11: gradation conversion section, 12: color co selector (selection section),

13: A / D conversion part, 14: dot control part.

[Industrial use]

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for converting a gradation of an image when printing a replica image having excellent image quality, such as a printed image or various high quality victorious hard copies.

More specifically, the present invention relates to a gradation conversion method of a novel image when producing a half tone copy image from a continuous gradation color photograph image as an original image.

[Prior art]

When trying to produce a variety of duplicate images, such as printing printed images using a color scanner or printing high quality hard copies using a scanner and a high-precision printer. For example, it is needless to say that when a continuous grayscale color photograph image is used as the original image, the continuous grayscale of the original image must be converted into halftones of the duplicate image.

The gray level conversion of the image above converts density information of each pixel of the original image into a duplicate image system.

As is well known, various reproduction methods (density display methods) have been adopted as a method of reproducing the density information possessed by the original in the duplicate image. It goes without saying that the conversion of the gradation is performed in these concentration display methods.

In addition, the gradation conversion is very closely related to the conversion of the density information of the pixel as well as the conversion of the color tone of the pixel, which will be described later.

Various methods are employed as the density display method of the above-described replicating image system, and representative examples thereof will be described below.

(Iii) Typically seen in the manufacture of printed images, the coverage of a given pixel is changed in accordance with the size of the dot (dot area% value).

In other words, density information is reproduced by changing the coverage of the pixel having a predetermined size according to the size of the dot.

This method is also referred to as multi-level area gradation display, and is applied to ink jet printers, melt thermal transfer printers (the thermal printers), and the like in addition to printing images.

(Ii) In the method of changing the size of the dot (multiple area), there is a method of changing the coverage of a predetermined pixel by the arrangement of dots of the same size.

This method is also referred to as binary area gradation display, and has been applied to the above-described application field, that is, a melt thermal transfer printer ink jet printer.

(Iii) There is a method of directly changing the density of the pixel itself of a predetermined size.

This is the same method as the continuous density reproduction system of conventional color photographing materials. This method is also called direct density gradation display and is applied to sublimation dye thermal transfer printers (sublimation printers). As described above, a duplicate image such as a print image or a high-quality printer image by various copying techniques from a manuscript image of continuous gradation (also referred to as a duplicate image in the present invention should be interpreted in the widest sense as described above). However, it is extremely important to faithfully reproduce the gradation and color tone of the original image with regularity on the duplicate image.

However, in spite of the progress of the current replication technology, the present situation has not solved the above-mentioned reproducibility problem reasonably.

This is based on the technique of faithfully reproducing the above-described state of the original image (including gradation and color tone) in the duplicate image, and also adjusting (modifying or changing) the state of the original image to a desired state. This is because the nonlinear conversion processing techniques (image gradation conversion technique, image gradation conversion technique) in the density region of the image to be lacked are unscientific and irrational due to the lack of rational theory.

This will be described below by taking an example of a manufacturing technique of a printed image, which is a technical field of a representative duplicate image.

The inventors of the present invention, such as the current monochrome scanner color scanner, the advanced plate making apparatus is basically a need for plate making and printing is not enough knowledge, and his design technique is a color separation theory by an unsystematic photo masking method It is thought that the frequent improvement of the synchronous machine was basically a coping therapy based on the color separation theory.

That is, in the conventional design technique of the scanner apparatus, when the gradation is converted from the continuous gradation image of the photographic document to the halftone gradation image of the printed image in the color separation operation, the color correction or color correction (color masking) is used as the first object. Because the gray level adjustment is considered as the second purpose, the quality of the print image is not stabilized and advanced.

As described above, in the conventional gradation conversion method from a continuous gradation image to a halftone gradation image, the density value at an arbitrary sample contact (pixel contact) of the continuous gradation image and the sample of the halftone gradation image corresponding thereto. There was no rational and universal means of correlating the half-dot percentage of dots in dots.

In order to reasonably produce a printed image, the inventors of the present invention prior to the improvement of the color correction (correction) technique of two core element technologies, gradation control and color correction (clour correction). Based on the idea that a technique capable of reasonably converting the density gradation of each pixel must be primarily important, the research has been intensively tried to break the limitations of conventional irrational and unscientific modulation techniques.

As a result, a novel gradation conversion method was developed that correlated the basic concentration value of an arbitrary sample point of the original imager with the halftone area percentage value of the sample point of the dot image. This new and rational scientific conversion method has been sufficiently applied to conventional plate making equipment, and also breaks down the limitations of the conventional color separation technology to create an excellent effect. No. 2-55204 was proposed.

The above-described technique by the present inventors uses a gradation conversion formula similar to the present invention in the gradation conversion of an image (however, as described below, the operating conditions of the gradation conversion formula are completely heterogeneous). In order to produce images reproducibly, there is still room for improvement.

The above room for improvement means that an integer for operating the gradation conversion equation is set from the measured concentration values of the raw images and H and S, and the measured concentration values of the H and S are inevitably uneven. If this does not solve the problem, it is impossible to produce a print image with good image quality as it is.

[Problem to Solve Invention]

The present invention is a novel image that can be applied to the field of producing various duplicate images in view of the problems in the method of converting the gray scales described using the production of the printed image as an example. It is to provide a manufacturing conversion method of.

That is, in the technique of producing a duplicate image, it is necessary to obtain image information from the original image (acquisition of density information), and to convert the image information into a gradation conversion mechanism (gradation conversion unit) of the reproduction image production device. The tone conversion is to be made reasonable by applying the tone conversion method of the image of the present invention to it.

In particular, the gradation conversion method of the image of the present invention uses a color photographic document as the original image, and is aware of the inevitable nonuniformity in the measured concentration values of H and S specified in the original image. By reducing the density and converting the density information value without the non-uniformity obtained by this to a specific gray scale conversion formula, the reproduced image according to the design can be produced with good reproducibility.

[Measures to solve the problem]

In the gradation conversion method of an image when the continuous gradation conversion of a color photographic original image is carried out to produce a duplicate image of a halftone gradation, the gradation conversion of the image is (i) the sharpest part (H) and the darkest part specified in the color photographic original ( A step of obtaining the concentration values (DH _av , DS _av ) of H and its vicinity and S and its sac by the concentration value of S), and (ii)) each pixel point (n points) ranging from H to S The process of obtaining the density D _n of each pixel point by scanning, and the color specified in the DX orthogonal coordinate system of the vertical axis (D axis) indicating the concentration value and the X-axis value (X axis) correlated with the amount of light. Using the density characteristic curves of photographic photosensitive materials contributed to photographic photographs, the representative concentration values (DH _av , DS _av ) of H and S and the density values (D _n ) of each pixel point are determined by the amount of light. an image information value (X _n) to the correlation step, (ⅳ) the amount of light to convert the image information value (X _n) correlating to the grayscale conversion Relates to a gray-scale transformation of the image, characterized in that comprising a step of changing a system promotes lightness value (Y) by using the.

Gradation Conversion

y = y _H + [α (1-10 ^-kx ) / (α-β)] · (y _s -y _H )

However, in the gray scale conversion formula

X: Basic light quantity value represented by X = (X _n -X _H )

That is, the image information value X _n correlated with the amount of light obtained from the density value Dn of an arbitrary pixel (n point) on the original through the density characteristic curve defined in the DX rectangular coordinate system, and the representative density value DH of the H portion. _{The difference} between the image information values X _H correlated to the amount of light corresponding to _av ).

y: gradation intensity value of the pixel on the duplicate image corresponding to an arbitrary pixel (n point) on the original

y _H: Gradation intensity value preset for H of duplicate image corresponding to H on original

y _s: Gradation intensity value preset for S of duplicate image corresponding to S on original

α: surface reflectance of the recording paper of the duplicate image

β: numerical value determined by β = 10 ^−γ

K: numerical value determined by K = γ / (X _s -X _H )

In the above formula, X _s represents an image information value correlated with the amount of light obtained from the representative concentration paper DS _av of the S section through the density characteristic curve defined in the DX rectangular coordinate system.

γ: each represents an arbitrary coefficient

Hereinafter, the technical configuration of the present invention will be described in detail.

In addition, the following describes a case in which a color print image is produced as a duplicate image by using the gradation conversion method of the image of the present invention, particularly a case in which a print image is produced using a color scanner. Therefore, this is for convenience of explanation, and it does not mean that the image conversion method of the image of the present invention is applied only in the case of duplication of color printed images.

First, in order to facilitate understanding of the present invention, an important concept of image information to be subjected to gradation conversion, that is, image information correlated with light quantity (hereinafter referred to simply as light quantity value) and its light quantity value More specifically, the method for setting the tone conversion curve (color separation curve) will be described.

As described above, the present inventors have made intensive examinations by making the setting technology of the gradation conversion curve (color separation curve, state reproduction curve) which forms the core of the color separation work reasonable. Among them, when manufacturing a conventional color plate (C / M / Y plate), for example, C plate which is a standard for plate making, the concentration value obtained through the R (red) filter of complementary color relation and the halftone area% value Instead of the prescribed technology for setting the color separation curve for C plate, the exposure value is determined by using the photo density characteristic curve of the sensitizer of the color photographic film in which the original image is photographed (the present invention refers to this as the light quantity value). Since the term "light quantity value" is included in the concept), the light quantity value is converted by a specific gray scale conversion formula to obtain the halftone area% value, that is, the color separation curve defined in the relationship between the light quantity value and the halftone area value. When set, based on the color separation curve, any image quality of the original image (e.g. under / over exposure, high key / low key) is extremely Is found that the original, the resulting print having excellent gradation characteristic with a variety of color blur the document, washed-out the document, and so on) the image (for example, Patent Application No. Heisei 1 years No. -135825).

In addition, the color separation curve for color plates defined in the relation between the above-described conventional density value and half-dot area% value, since the D-axis is focused on the image information from the density, which is the vertical axis, in the characteristic curve of the photographic film photosensitive material, It is called color separation curve. On the other hand, the color separation curve for the color plate defined in the relationship between the light quantity value and the halftone area% value of the present invention regards the image information from the light quantity axis of the horizontal axis (X axis) in the characteristic curve of the color axis X color separation. It is called a curve.

As described above, the present invention does not depend on the image quality of the color original (which may be a cover type, a negative type, a transmissive type, a reflective type, etc.) to be plated, for example, an manuscript of an over / normal / under exposure, high key. In order to produce prints of excellent image quality from low-key originals, various color-blurred or fading originals, light values rather than density values are used as image information for gradation. This is a point that is remarkably different from the prior art. The reason why the light intensity value is not the density value of the original image in the tone conversion (conversion to continuous dot gradation) is as follows.

In order to rationally convert a variety of original images having different image quality, the subjects incident on the color film sensitive material are not used by using the "concentration value", which depends on the photograph density characteristic curve inherent in the camera film photosensitive material. When the light quantity value from (being literally the base of the original image, the actual image, the actual image) is the image information which does not depend on the characteristic curve of the photo density (characteristic of the photosensitive material), it is reasonably uniform in any image quality. It is due to the creativity of the present inventors and the like that it can be converted to gray scale.

Next, the method of setting the X-axis color separation curve of each color plate, for example, C plate, using the light quantity value will be described.

First, a light quantity value must be obtained from the color photograph document as image information.

The light quantity value can be easily obtained from the photographic density by using the characteristic curve of the color photographic film photosensitive material (sensitizing emulsion) on which the original image is photographed, the so-called photographic characteristic curve. The photographic concentration characteristic curve may be represented by a D-X rectangular coordinate system in which the vertical axis represents the concentration D and the horizontal axis X represents the exposure amount. In order to obtain the light quantity value, the photograph density characteristic curve of the color photographic film photosensitive material on which the original image is photographed must be functionalized. Thereby, the light quantity value Xn of the corresponding pixel can be obtained from the density value Dn of any appeal point (n point) in the original image. The photographic concentration characteristic curve can be functionalized as a technical data from each limb sensitizer maker.

For example, in FIG. 1, the photoconcentration characteristic curve of the etachrome 66 and the professional film (daylight) by EK company is shown. The method of functionalizing the photographic concentration characteristic curve is not particularly limited, and may be in accordance with a desired method. Needless to say, as shown in Fig. 1, the photosensitive emulsion of R / G / B of the color photographic film has respective characteristic curves, so that they must be functionalized to obtain a light quantity value for the production of the corresponding color plate.

Table 1 shows the results. In addition, in Table 1, in order to formulate the photograph density characteristic curve as accurately as possible, a plurality of classifications are provided.

Photo Concentration Characteristic Table

TABLE 1

In the present invention, as shown in FIG. 1, when the photograph density characteristic curve is functionalized, the scale of the X axis indicating the light amount value represented by the scale (scale) of the D-axis representing the density value of the color photographic document and the logE of the subject (real image) D and X are functionalized as the same thing.

Scaling about this D-axis and X-axis was performed from the following viewpoint, and it seems to be very rational for this inventor.

That is, in the photographic concentration characteristic curve, the position of the logarithmic value logE = logI × t of the exposure dose E is given to the X axis, and this physical quantity is evaluated by the logarithmic distinction characteristic of the contrast of the human eye.

On the other hand, the physical quantity regarding the concentration of the D axis is also evaluated algebraically in the human view. Therefore, it is considered that there is no unreasonableness even when the D-axis and the X-axis are correlated under the same scaling.

In addition, in this invention, said graduation is a kind of simple method, Needless to say, it is not limited to this. For example, you may function by the numerical relationship of the D-axis and X-axis shown in FIG.

Including the relative meaning mentioned above, in the present invention, the physical quantity of the X-axis is expressed by the term "light quantity value", which is a concept including an exposure value.

As described above, the present invention is not based on the density value (Dn value) of the color photograph document in gray scale conversion, but is an image information value provided by a subject (real image, real diameter), that is, a light quantity value represented by the X axis ( Is based on Xn).

As described above, as shown in Table 1 by the functionalization of the photo-concentration characteristic curve, since the Dn value and Xn value are correlated by the function of X = F (D), the Xn value can be easily obtained from the Dn value.

As described above, the light quantity value Xn contributed by the subject (real image) can be obtained. Subsequently, it is only necessary to obtain the X-axis chromatic separation curve that focuses on the color separation curve, that is, the light quantity value in place of the conventional D-axis color separation curve, which focuses on the conventional density information value, by using the Xn value obtained in this way and the gray scale conversion equation. Further, the light quantity value Xn of the pixel on the corresponding subject (real image) is obtained from the density value Dn of any pixel (n point) on the color photograph document under a predetermined photograph density characteristic curve, and the Xn value is obtained by the gray level. By substituting the conversion equation, the halftone area% value, which is the gradation intensity value, is calculated, and the X-axis color separation curve is set.

The operation of the gradation conversion formula is performed by using the light intensity values X _H and X _s corresponding to the density values D _H and D _s of the sharpest part H and the darkest part S specified in the original image.

However, the central problem of the present invention is to recognize that unevenness is inevitably generated in the concentration measurement values of the sharpest part H and the darkest part S, and to solve the serious drawback caused by this.

This advantage is described later in detail.

In the operation of the gradation conversion expression intensity values (Xn) unless place by converting the basis of the light quantity value (X) as described above andoena which the dot area% values (y _H, y _s) previously set in the H section and the S section It is a means for studying.

And in order to make C plate of halftone gradation, the color generator's Dot generator only needs to operate according to the X-axis color separation curve for the C plate.

Next, the derivation process of the gradation conversion equation of the present invention and its characteristics will be briefly described.

In producing printed images with halftone gradation, the gradation conversion formula for calculating the numerical value (Y) of the halftone area set for each pixel in the original image is a density formula (photo density, optical density), which is generally accepted.

That is, D = log I ₀ / I = log 1 / T

Where I ₀ = incident light

I = reflected or transmitted light

T = I / I ₀ = derived based on reflectance or transmittance.

The general formula for this concentration D is applied to plate making and printing as follows. The plate making, the concentration (D ') in the printing = log I _0/1 = log (in the reflectance of the area × paper) / {(unit area-dot area) × the surface reflectance of the reflectance + tone × ink paper} = log αA / [α {A- (d ₁ + d ₂ + …… d _n )} + β (d ₁ + d ₂ …… d _n )]

Where A: unit area

dn: each dot area in the actual unit area

α: reflectance of cut paper

β is the surface reflectance of the printing ink.

The present invention uses the light quantity value instead of the density value as image information on the basis of the density equation (D ') relating to plate making and printing, and the basis of sample points (pixels) and (n points) of the original image in continuous gradation. The gradation conversion formula is derived so that the correlation between the light quantity value X and the numerical value Y of the half-area area value of the halftone at the sample point of the printed image corresponding to the halftone gradation corresponds to the theoretical value and the actual value.

In the operation of the gradation conversion equation of the present invention, the parameters of y _H and y _s are generally integerized, for example, 5% in Y _CH of C plate, 95% in Y _CS , and Y _MH = Y in M and Y plates. _{The half-} dot area% of _YH is used as 3% and Y _MS = Y _YS as 90%. In the operation of the gradation conversion equation, when the Xn value obtained in relation to the Dn value measured by the densitometer is used and the percentage resin (% value) is used for y _H = Y _s , the y value is also calculated as a percentage value.

In the operation of the gradation conversion equation of the present invention, the value of another important parameter γ may be considered to be generally purified in setting the color separation curve for the C plate for the following reason. That is, you may fix at gamma value = 0.45 in setting of the X-axis color separation curve for C boards. This is derived from the fact that the present inventors developed a gradation change equation employing a density value as an image information value during the development of the gradation conversion equation of the present invention, and is supported by many experimental examples.

However, the parameter γ is a parameter that can change the shape of the color separation curve in other words, that is, it is an extremely important parameter because it is possible to produce a printed material having a desired gradation characteristic by controlling the γ value for the purpose. It doesn't happen.

The numerical setting of the gradation conversion parameter of the present invention is intended to faithfully reproduce the state of a given subject (real image) to the print image to the last, and to produce a print image in which the state is consciously adjusted (modified or changed). It depends on the position. In the latter case, by changing the gamma value consciously, the shape of the X-axis color separation curve can be changed to a desired one (i.e., one having a desired gradation), so that print images of various states can be obtained. For example, the shape of the X-axis color separation curve should be close to γ when the upper part is in the shape of 상태 (when the emphasis is on the state of H to mid-tone), and vice versa. (When you want to emphasize the state of the midtone to the shadow part) What is necessary is just to let γ be a negative value.

In the operation of the gradation conversion formula of the present invention, it is also possible to use it by transforming as follows, as well as by using it arbitrarily, deforming, inducing and the like.

y = y _H + E (1-10 ^-kx ) · (y _s sy _H )

Provided that E = 1 / (1-β) = 1 / (1-10 ^γ )

In the above modification, α = 1.

This is, for example, 100% of the surface reflectivity of a printing paper (substrate) used to express a print image. As the value of α, any value can be taken, but in practice, the value may be set to zero in order to zero the whiteness of the species.

According to the modification (α = 1.0), y _H can be set to the brightest part H of the printed image as desired and y _s to the darkest part S, which is a great feature of the gradation conversion equation. This means that X = (X _n -X _H ) = 0 according to the definition in the outermost part H of the printed image, and X = X _S -X _H in the darkest part S,

That is,-k X =-γ (X _S -X _H ) / (X _s -X _H ) =-γ

It is obvious from becoming. By using the gradation conversion formula (modified example of α = 1) of the present invention as described above, it is always possible to set y _H and y _s as desired in the H and S portions of the printed image. It is extremely important to consider. For example, setting desired values for y _H and y _s in a printed image and changing the value of γ (where α = 1.0) yields various X-axis color resolution curves, thereby increasing their X-axis color resolution curves. The printed image obtained by the ab can be easily evaluated in relation to the? Value.

Particularly important in plate making practice is that the X-axis color decomposition curve obtained in the present invention is different from the conventional D-axis color separation curve to display gradation characteristics and state characteristics ranging from H to S of a double-chain image as a final product. to be.

That is, the platemaking worker can accurately predict the finish (state) of the final printed image through consideration of its shape from the X-axis color separation curve obtained under the predetermined y _H y _s and gamma values. This is due to the great feature of the gradation conversion method of the present invention that each set X-axis color separation curve converges to one and the same color separation curve for a plurality of original images having different image quality (for example, different exposure conditions). This becomes the conventional D-axis color separation with respect to such large Irv (adopted value y _H, y _s, and γ is) is obtained that the image quality is increased Irv car corresponding to different respective original image, its shape is complicated. Therefore, the plate making operation cannot accurately predict what the final printed image will be only by considering his curve.

The meaning of the above is extremely important and the judge can accurately predict the final printed image by displaying the X-axis color separation curve of each color plate (C, M, Y) and the ink plate (B), for example, by displaying a monitor. As a result, various calibrations can be made unnecessary. In other words, the present invention enables direct plate making (Direc plate making method).

In the operation of the gradation conversion formula of the present invention, the normalization may be performed such that the k value is a γ value, that is, the (X _{H to} X _s ) value is 1.0. By normalizing the dynamic range of X _{H to} X _s to 0 to 1 = 1.0, the comparative examination between the X-axis color separation curves becomes easy and the calculation of the gradation conversion equation becomes extremely easy. Originally, the amount of light X of each image quality in the dynamic range also changes in accordance with its normalization, but since it is a relative change, it does not cause any trouble in setting the color separation curve. In addition, in the following description, calculation of y value is computed using the value after normalization.

The X-axis color separation curve of each color plate for the multicolor plate (generally, four plates of C plate, M plate, Y plate, and B (mud) plate) is operated by operating the gray scale conversion formula of the present invention. In order to do this, it can be performed in the same shape as the above C plate under the desired plate making design.

The above description is an outline of the gradation conversion technology employed in the gradation conversion section, which is a core component thereof, when producing a printed image using a color scanner.

Next, the improvement of the gradation conversion unit for incorporating the manufacturing conversion technique in the color scanner will be described.

It goes without saying that the gradation conversion formula is incorporated in the gradation conversion section of the color scanner for producing the printed image, and the gradation conversion is performed by the gradation conversion formula.

As described above, in the gradation conversion formula, the brightest part (H) and the darkest part (S) are designated on the color photograph document, and the concentration values (DH _H , D _s ) of H and S are measured, and the density values (D _H , D _s ) corresponding to the light quantity value (X _H , X _s ) is obtained, and using the light quantity value (X _H , X _s ) in the same shape as other barometers (γ value, y _H , y _s value). The gradation conversion equation is operated to achieve gradation conversion (setting of the X-axis color separation curve).

In this case, the most important problem is that unevenness inevitably arises in the measurement of the concentration values of H and / or S of the color photograph document.

The nonuniformity of the measured concentration values of H and S only adversely affects the state of the color print image produced after the gradation conversion, that is, the gradation gradation, color tone, and gray balance (characteristic of surface hardness). This causes an extremely important problem that the intended print image is not produced.

Incidentally, Table 2 shows the results of investigating the non-uniformity of the measured concentration values of H and / or S with respect to various originals (thin originals, standard originals and dark originals) at the time of the C plate. In addition, the result of Table 2 was investigated using the sample color photographic document (Daylight ASA 100 by F company) the color scanner 455 by ISOMET company.

Nonuniformity in the Measurement Concentrations of H and S

TABLE 2

It was investigated how the nonuniformity of the measured concentration values of H and / or S affected the color reproduction of the halftone gradations after the Fujichrome 100 and Professional D (Daylight) gradation conversion. The results are shown in Tables 3 to 7. Also,

Table 3 shows light color film originals: density range of comparative center originals, 0.175 to 2.225.

Table 4 shows the standard color film originals: density range from the comparative center, 0.300 to 27.00.

Table 5 shows the dark color film originals: density range of the comparative center originals, 0.500 to 2.750.

Table 6 shows the extremely light color film originals: the density range of the comparative center originals, 0.125 to 1.850.

Table 7 shows the results of using the extremely dark color film originals: the density range of the comparative center originals and the color film originals of 0.900 to 3.100, respectively. Tables 3 to 7 were prepared under the following conditions.

(Iii) The daylight film made by F Company was used as a subject of examination of the nonuniformity of the measured concentration values in H and S.

(Ii) In the operation of the gradation conversion equation, y _H = 5%, y _s 95%, γ = 0.45, on the premise that a C plate was produced. It goes without saying that the numerical values in the tables are the y values (the halftone area%) which are the calculation results of the gradation conversion equation.

In Tables 3 to 7, the headings of the tables indicate color film manuscripts (that is, non-uniformity of measurement, hereinafter referred to as comparative centric manuscripts) in which H and S measurements were performed according to the plate making design. The comparative manuscript and the non-uniform manuscript should be reviewed.

In each table of concentration column Denotes the control point of the gradation conversion, and the following numerical value thereof indicates that the density range value (dynamic range) The concentration value at the control point increased by the ratio of.

From Tables 3 to 7, it is easy to see how the% of halftone area is different from that of the comparative manuscript due to the nonuniformity of the measured concentration values in the control points.

Light color film originals (density range of comparative center originals = 0.1750-2.5000 = 2.3250)

TABLE 3

Standard Color Film Originals (Density Range of Comparative Center Documents = 0.3000-2.7000 = 2.4000)

TABLE 4

Dark Color Film Originals (Comparative Center Density Range = 0.5000-2.7500 = 2.2500)

TABLE 5

Extremely light color film originals (density range of comparative center originals = 0.1250-1.500 = 1.7250)

TABLE 6

Extremely dark color film originals (density range of comparative center originals = 0.9000-3.1000 = 2.2000)

TABLE 7

Tables 3 to 7 above were prepared in consideration of the nonuniformity of the concentration measurement in Table 2, and clearly indicate that a relatively large deviation occurred in the plate making design value at each control point. Especially The control point of the back is an important area for producing a print image having excellent image quality, and there is a large gap in the id control system.

Therefore, in order to produce a printed image according to the plate making design, it is essential to clearly recognize that the nonuniformity of the measured concentration values of H and or S means and to solve the problem.

The nonuniformity of the measured concentration values of H and S is inevitable when a color photograph (film) document is used as the original image.

Its main cause is due to the size, shape, particle dispersion state of the silver particles in the color film emulsion, and the size of the aperture (or slit) on the color scanner side. In the density measurement of H, the scanning luminous flux (scanning luminous flux) transmits (or reflects) a predetermined pixel of the original, and is then photoelectrically converted through an aperture of a predetermined size corresponding to the scanning pixel to measure the density value of each pixel.

2 shows the relationship between the silver particles and Aperture.

The size of the silver particles contained in the R / G / B fluid charge of the color film is generally 1 to 3 µm ² , while the aperture of the aperture is generally 1 to several mm.

In the gradation conversion section of the color scanner for producing a printed image, the gradation conversion operation is performed by using the gradation conversion formula. Therefore, the head of the color scanner is first placed in the designated H and S areas, and the density measurement of the H and S is not performed. You must. At this time, the above-described nonuniformity on the side of the silver particle and an incorrect arrangement of the H portion on the aperture side interact with each other, resulting in nonuniformity in the measured concentration values of H and S.

That is, when the density measurement of H and S in the color photographic document designated by the plate making designer, the plate making operator, or the like is performed,

It is difficult to accurately arrange an aperture having a predetermined aperture ratio in which mining (measured the amount of reflected light or transmitted light from an original) for concentration measurement is carried out on designated H and S sites.

Even if the aperture is accurately positioned with respect to the designated portions of H and S, there may be a non-uniformity of the above-described silver particle size in the region, so that an optimal portion of H and S may exist in the vicinity thereof ( The presence of the nonuniformity on the silver particle side is easily understood since the concentration measurement of the sites of syntactic H and S is performed by observing the site with a magnifying glass. The concentration may be measured at the site of H and S, resulting in non-uniformity in the concentration measurement of H and S.

In the color scanner for producing a printed image, in order to solve the defect caused by the nonuniformity of the measurement concentrations of the H and S, the density measuring unit of the color scanner is representative of the sharpest part (H) and its vicinity. The concentration value (DH _av ) and the representative concentration value (DS _av ) at the darkest part (s) and its vicinity are configured to run out. The gradation conversion section of the color scanner obtains the corresponding light amount values X _H and X _s from the representative concentration values DH _av and DS _{av and} performs gradation conversion by the gradation conversion equation.

In the present invention, the method for determining the representative concentration values (DH _av , DS _av ) is not particularly limited as long as it solves the nonuniformity of the measured concentration values.

For example, it is needless to say that the mean, mode, standard deviation, etc. may be used as the representative concentration values (DH _av , DS _av ). In addition, in the following description, it demonstrates using the Ping bacteria concentration difference as representative concentration value.

What is necessary is just to measure the average density | concentration value in the said sharpest part H, its vicinity, and the darkest part S, and its vicinity by the method suitable for the structure of a color scanner. For example, in the case of the drum type scanner, the operator may perform the drum while moving the drum or may give the vibration to the aperture portion. In the case of a flat bed, for example, the density information values of the pixels around the predetermined pixels stored in the CCD may be averaged. In addition, ultra-thin glass fibers may be combined with a desired number, and the concentration values may be measured and averaged for each glass fiber.

In the case of obtaining the average concentration value, for example, it is sufficient to measure three to five times from many experimental examples to ping equalize the outermost part H in the measurement area. This measurement number may be appropriately determined in consideration of the kind of film used, the structure of the aperture, and the like.

Next, the gradation improvement effect of the halftone gradation image (printing plate for C plate) of the scanner output when the nonuniformity of the measured concentration values of H and S is adjusted is shown in Tables 8-11.

In the present invention, the effect of improving the gradation characteristics of the halftone gradation image of the scanner output is (i) when the nonuniformity of the measured concentration values of H and S is adjusted by the average concentration values (DH _av , DS _av ), and (ii) the average In addition to the adjustment of the concentration values DH _av and DS _av , the gamma value of the gradation conversion equation is also adjusted (moreover, the reason why the gray scale characteristic is reasonably changed by the adjustment of the gamma value is as described above).

In Table 8-9, Table 10-11 shows the improvement effect in the case of said (ii). Comparing and reviewing Tables 3 to 7 and Tables 8 to 9, and Tables 10 to 11, it can be seen that the entry and the approach of (ii) are extremely effective.

In addition, Tables 8-11 are created on condition of the following.

Sample color film original (Daylight film made by F company): Standard quality color document

Concentration range of film originals based on adjustment management: 2.4000 (0.3000 to 2.7000)

Gradation conversion parameters: y _h = 5%, y _s = 95%

γ value = 0.4500 for Tables 8 to 9

γ value = Table 10 to Table 11 adjustment

In addition, the heading of each table indicates the degree of nonuniformity with respect to the concentration value of H (0.3000) and the concentration value of S (2.7000) of the reference manuscript. Needless to say, the degree of nonuniformity is improved because the nonuniformity in Tables 3 to 7 is averaged and adjusted.

Range of non-uniformity of measurement concentration value: H part ± 0.0125, S part ± 0.0500

TABLE 8

Range of non-uniformity of measurement concentration value: H part ± 0.0100, S part ± 0.0250

TABLE 9

Range of measurement concentration non-uniformity: H part 0.0125, S part 0.0500

TABLE 10

Range of measurement concentration: H part 0.0100, S part 0.0250

TABLE 11

Next, an example of the apparatus configuration of the color scanner for producing the print image will be described with reference to FIG.

The color scanner according to the present invention has a density measuring instrument capable of outputting the average concentration values (DH _av , DS _av ) from H and S and its vicinity specified in the original image as compared with the conventional ones as described above, and the average concentration values. It is characterized by the fact that there is provided a gradation conversion mechanism that performs gradation change by a gradation conversion formula. That is, since the other components are the same as the conventional ones, the conventional scanner can be reconstructed in the scanner to which the gradation conversion method of the image of the present invention is carried out only by incorporating the above mechanism.

In FIG. 3, the drum type color scanner includes a detection unit 1 for reading an original, a color separation unit 2 for converting an output signal of the detection unit 1 into color separation signals of Y, M, C, and K, and the gray level. It is composed of four blocks of a gray scale adjusting section 3 for obtaining an appropriate halftone gradation using a conversion formula and an output section 4 for performing raw film exposure by laser light based on the output signal of the gray scale adjusting section 3. In the configuration of the color scanner, the block of the color separation unit 2 and the output unit 4 has a configuration similar to that of a conventional color scanner, and the detection unit 1 includes the brightest portion H, its vicinity and the pressure portion. (S) and a mechanism for detecting the average concentration value from the vicinity thereof are different from the conventional one in that the tone adjustment unit 3 is subjected to the tone conversion based on the above tone conversion equation.

The detection unit 1 detects transmitted light or reflected light of each pixel of the color film document 5 such as a photomultiplier plate, and outputs R, G, B, USM signals as current values, and converts these signal rules into A / V conversion. In section 6, the signal is converted into a voltage signal. In addition, as described above, the detection unit 1 is a mechanism capable of detecting transmitted light (or reflected light) for obtaining the average concentration values DH _av and DS _av from the H and S and its vicinity.

The color separation unit 2 converts the voltage signals of the R, G, B, and USM signals of the detection unit 1 into logarithmic values in the log amplifier 7 and converts them into concentrations. In the basic masking (BM) 8 The gray (K) component is separated from the concentration, and each component of Y, M, and C is separated.

Further, the transmitted light (or reflected light) detected in the log amplifier 7 in order to obtain the average concentration values DH _av , DS _av by the detection unit 1 is further converted into a voltage signal, which is then logarithmically calculated to obtain the average concentration value.

This is sent to the gradation conversion section 3 to be described later to become an important integer term for the operation of the gradation conversion formula.

Next, in the Color Correction (CC) 9, the Y plate component, M plate component, and C plate component are controlled for each original color of R, G, B, and YMC, and the gray component of the original is again UCR. In the UCR (Under Color Removal) or UCA (Under Color addition) of the / UCA unit 10, the ratio expressed by the three editions of Y, M and C and the ratio expressed by the k edition are determined. Here, after the Y, M, C, and K components are obtained, the test results are obtained by calculating the half point execution area of each component by ye ', me', ce ', and ke' in the Gradation Control Unit of the IMC. Inverse log conversion in the inverse log conversion unit, but in the scanner configuration as shown in FIG. 3, the gradation conversion unit 11 is used in place of the density control unit and the inverse log conversion unit, where Y 'from Y, M, C and K. to me, me ', ce', and ke '. The gradation conversion section 11 passes the algorithm of the gradation conversion formula inside, and obtains ye ', me', ce ', and ke' by applying the gradation conversion time to Y, M, C, and K, respectively. The gradation converting section 11 holds a gradation conversion algorithm as software, a general-purpose computer having A / D and D / A I / F (interface), and an electric circuit and algorithm embodied by a general-purpose IC using the algorithm as logic. It can take various forms such as an electric circuit including a ROM having a result of calculation, a PAL embodied by an algorithm as an internal logic, a gate array, a custom IC, and the like.

The effective dot area ratio obtained by the gradation converter 11 is input to the color channel selector 12, and the color channel selector 12 sequentially outputs ye ', me', ce ', and ke'. . This output is A / D converted by the A / D converter 13 and input to the output unit 4. The output section 4 controls the laser beam in the dot control section 14 based on the output of the gradation adjustment section 3.

As described above, the present invention is not limited to the field of producing a printed image as the field of producing a duplicate image.

As described above, the print image is not limited to the production field as the production field of the duplicate image.

As an example of application of the gradation conversion method to the image of the present invention, a fusion type thermal transfer printer capable of changing (multipleizing) the size of dots in a reproduction system of a replica image as described above, and a sublimation transfer type thermal printer which changes the shade of the pixel itself The present invention is applied to a digital copying machine (color copy), various printers (ink jet type, bubble jet type), etc., to change the tone by dot arrangement.

In order to apply the gradation conversion method of the image of the present invention to the above-described various application fields, (i) image information values and / or image information electric signal values relating to the density of color photographic documents in the apparatus for producing each duplicate image. The light quantity value corresponding to the log or digital), and (ii) the light quantity value is converted by the gray scale conversion formula in the image conversion processing unit (gradation conversion unit) of the device under the gray scale conversion formula (i) and the y value (gradation) The current value, the voltage value, or the application time of the recording portion (recording head) of the device,

Size of halftone area

Number of dots per pixel (constant area) and its arrangement

By converting the abilities of a given pixel (constant area) itself, and reducing it, the gradation of the original image can be changed over the entire dynamic range of H to S by gradation expression methods such as size modulation, density modulation, or density modulation. You can legally and faithfully convert the replicas to 1: 1.

For example, FIG. 4 is a schematic diagram explaining the device configuration of a digital copying machine (color copy) using a known laser beam. As shown, the device configuration is almost the same as that of the color scanner of FIG. In Fig. 4, the color photographic document 5 is adhered to the rotary drum, but it goes without saying that even a flat bed type document acquisition mechanism.

The conversion unit 11 of FIG. 4 has the algorithm of the gradation conversion formula of the present invention therein, and applies the gradation conversion formula to each of the Y, M, C, and K components in the form of a color scanner and wound, thereby applying the gradation intensity value y. Obtain In addition, as the y value, a value corresponding to the reproduction gradation number, for example, 256 gradations, may be obtained. In the case of 256 gradations, when y _H = 0 and y _s = 255 are set in the application of the gradation conversion equation, images of 0 to 255 (256) gradations are duplicated in the dynamic range from _H to S.

In FIG. 4, the latent image is imaged on the photoconductor based on the lattice intensity value y corresponding to the halftone of the photographic plate by the laser beam from the laser beam generator 15, that is, the ratio of pixels covered by the predetermined pixel block. Is formed.

That is, the area ratio of the pixels obtained by the conversion unit 11 is input to the color channel selector 12 to sequentially and selectively output ye ', me', ce ', and ke'. This output is A / D converted and input to the output unit 4.

The output unit 4 controls the laser beam generator 15 in the dot control unit 14 based on the output of the gradation adjustment unit 3.

Although the gradation conversion method of the image of the present invention is not shown, it is incorporated in the gradation adjustment units of the shapes shown in Figs. 3 to 4 of the other copying image production equipment, and the gradation conversion operation of these devices can be rationalized.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples.

Color film originals, color scanners, and color proofing used in the examples are as follows.

(Ⅰ) color film manuscript

As a color film manuscript, a female figure of standard quality photographed with Fuji Chrome 100D, 4 × 5 manufactured by F Company was used.

The manuscript was measured with an X-RITE densitometer, that is, 2.72 in the H section 0.31 and S section, and its dynamic range was 2.41.

In addition, since the measured concentration values of H and S of the color film document are almost the same as those of Table 4 (standard color film document), the color due to the nonuniformity of the measured concentration values of H and S to be performed in the stage of plate making design before color separation. The data on the stabilization effect of the gray scale of the dynamic output color image by adjusting the gray scale of the scanner output color image and adjusting the measured concentration values of H and S according to the present invention or by adjusting the γ value in the gray scale conversion equation are shown in Tables 4 and 9. And Table 11.

(Ii) color scanner

455 DIGITAL COLORSCANNER made by ISOMET was selected as a calorie scanner used for color separation, thereby giving a function.

① the mean concentration values (DH _av) of the mean concentration values (DH _av) under the S region and its vicinity according to the density measurement portion H and its vicinity region was to be displayed and output. The average concentration value was measured m times (m is an arbitrary integer), and its arithmetic mean was incorporated into digital display and output. In this example, m was set to 5 times.

(2) The gradation converting section is equipped with software which can convert the optical lychee (normalized light quantity value) Xn obtained from the density value Dn by the gradation conversion formula of the present invention into a halftone area% value (y). Moreover, the software which automatically obtains the gamma value which gives a desired dot area% value, for example, 50% in the site | part of a desired light quantity value (or concentration value) was also mounted.

(Iii) color correction

As the color correction after color separation by a color scanner, the D company chrominine method was adopted.

(Iii) color separation

In the experiment, the effect of the present invention, that is, the effect of reducing the non-uniformity of the measured concentration values of H and S of the color film document, specifically, the effect of keeping the non-uniformity of H and S within the range of 0.0200 and 0.0500, respectively In addition, in order to confirm the effect of adjustment by the coefficient [gamma] value in the above (Gradation Conversion Formula) of the present invention, two persons of the worker and the worker were selected. Then, H and S portions were set on the color film document, and color separation was performed so that the former effect on the worker's head and the latter effect on the worker's body could be confirmed. The operating conditions of the gradation conversion formula for setting the color separation curve of each color plate (C, M, Y version) are as follows.

C version: y _H = 5% y _s = 95%

M = Y version: y _H = 3% y _s = 90%

γ value: 0.45 (fixed method) or arbitrarily changed (see Tables 10 to 11)

The former measured 10 concentrations of H and S, respectively, using a color scanner injection head. In addition, each measurement concentration is an average of five times.

The results are shown in Table 12.

In the shape of A, the concentrations of H and S were measured five times. The results are shown in Table 13.

Measured concentration values of H and S measured by A

TABLE 12

Concentrations of H and S measured by

TABLE 13

As a result, the range of nonuniformity of the measured values of H and S by A is 0.3100 to 0.2940 = 0,0160,2.7320 to 2.6840 = 0.0480 in Table 12.Either H is in the range of 0.020 and S is 0.0500 in Table 9. It was confirmed to enter. In addition, the color separation was performed based on the data of №7 in Table 12, but satisfactory results were obtained.

In addition, it was confirmed that the range of the nonuniformity of the measured values of H and S by E was within the range of the nonuniformity defined in Table 9 as a wound form in Table 13. The color separation was carried out based on the data of №2 in Table 13, but satisfactory results were obtained with the same shape.

Next, the color separation operation is performed using the data of №2 in Table 13, and the γ value in the gradation conversion equation of the present invention is adjusted so that the color separation operation due to the data of №7 in Table 12 is fixed (γ = 0.45). It was tested whether the result was obtained. The reason for employing the data of №2 in Table 13 is that the degree of data distortion is the largest with respect to the data of №7 in Table 12 and is considered to be an optimal comparison case for confirming the effect of the present invention.

As shown in the remarks column of Tables 12 to 13, the trial design data shows that the γ value in the tone conversion equation is γ = 0.45.

% Of halftone point area of plate C from 1/4 in case of № 7 (Table 12) of the former: 50.4104

% Dot value of C part of 1/4 part in case of №2 (Table 13) of o: 49.3713

Both are not identical. In other words, both are not strictly printed images of the same gradation.

Thus, the value of gamma was adjusted to change gamma = 0.45 to gamma = 0.4921, and color separation was carried out using data of No. 2 (Table 13). In addition, when γ = 0.4921 The% value of halftone area of negative C plate is 50.4089 (%).

Comparing the state of the color correction printed image of the former and A produced as described above, that is, the two images were almost homogeneous.

As a result of the above experiment, the present invention can achieve the effect as scheduled, and by specifying the positions of H and S in advance, the size, shape, distribution irregularity of the silver particles in the photographing material, and differences in the working instructions of the scanner operator It is possible to produce a color print image having a stable state (gradation and hue) at all times without any adverse effect on the color scanner output color plate image due to the nonuniformity of the measured concentration values of H and S of the color film document.

[Effects of the Invention]

When using a color scanner for making a print image or an image scanner for making another high-quality replica image, when creating a continuous image of halftone gradation from a color photograph document of continuous gradation, from the sharpest (H) to the darkest (S) It is extremely difficult to produce a duplicate image having a gradation intensity value (for example, a half-dot percent value, a coverage ratio of pixels by dots, etc.) as designed over the entire dynamic range of.

In other words, it is extremely difficult to convert the gradation according to the design to produce a desired duplicated image stably and efficiently.

In the gradation conversion method of the image of the present invention, the gradation conversion is reasonably controlled by a specific gradation conversion equation, but the density measurement of H and S of the original for setting the initial conditions for the gradation conversion must be performed. However, the measurement of the concentrations of electricity H and S is accompanied by unavoidable nonuniformity, and it can be quantitatively determined from the output result of the electric gradation conversion that the measured concentration value has a very bad effect on the gradation conversion. The nonuniformity by measuring the concentrations of H and S makes a difference in gradation intensity values close to 10% in H to midtones (medium, light and dark), which are important areas for gray scale reproduction. This is extremely influential on human vision.

In order to produce a high quality replica image by applying the gradation conversion method of the image of the present invention, a density measuring unit for averaging the density measurement nonuniformity of electricity H and S in various apparatuses for replicating images to obtain an average concentration value, and Although it is necessary to incorporate a tone conversion unit for performing tone conversion by the tone conversion unit of the invention, it is possible to always produce a duplicate image as designed.

The above is extremely significant and, for example, in the production of printed images, it contributes to the efficiency of plate making, namely, reduction or elimination of hand plate, saving of related materials, shortening of working time, shortening of product delivery time, and the like.

In addition, since manufacturing conversion is performed rationally and quantitatively in the production of printed images, quantitative and scientific education of the operator regarding color separation operations (gradation conversion bleaching operation, the latter including color correction), and customers Excellent effect in terms of realization of needs.

Of course, the above point is not limited to the production of a print image, but can also be said of a book image.

Claims (4)

In the gradation conversion method of an image when gradation of a color gradation image of a continuous gradation to produce a duplicate image of a halftone gradation, the gradation conversion of the image is (i) the sharpest part (H) and the darkest part (S) designated in the color manuscript. Obtaining a representative concentration value (DH _av , DS _av ) of H, its vicinity, and S and its neighborhood (ii) as a concentration value of (ii) scanning each pixel point (n point) from H to S Process of obtaining the density value Dn of each pixel point (i) For photographing a color photographic document defined in a vertical orthogonal coordinate system of the vertical axis (D axis) indicating the density value and the (X axis) indicating the image information value correlated with the amount of light. Converting the representative concentration values (DH _av , DS _av ) of the H and S and the density values (Dn) of the pixel points into image information values (Xn) correlated with the amount of light using the provided density characteristic curve Iii) Gradation steel using the following gradation conversion formula for the image information value Xn Value (y) of a gray-scale image transformation step being configured to convert the. Gradation Conversion y = y _H + [α (1-10 ^−kx ) / (α-β)] · (ys, -yh) However, in the gradation conversion formula X: Basic light quantity value represented by X = (X _n -X _H ). In other words, from the density value Dn of an arbitrary pixel (n point) on the original, the image information value X _n correlated with the amount of light obtained through the density characteristic curve defined in the DX rectangular coordinate system and the representative concentration of the H portion (DH _av) ) Represents the value of the image information value (X _H ) correlated with the corresponding amount of light. y: gradation intensity value of the pixel on the duplicate image corresponding to an arbitrary pixel (n point) on the original. y _H : The gradation intensity value preset for H of the duplicate image corresponding to H of the win image. y _s : Gradation intensity value preset for S of the duplicate image corresponding to S on the original. α: surface reflectivity of the recording paper of the duplicate image β: numerical value determined by β = 10 ^-γ K: Numerical value determined by K = γ / (X _s -X ₁₁ ), wherein X _s is a concentration characteristic curve defined in the DX rectangular coordinate system from the representative concentration value (DS _av ) of the S part. Represents the image information value correlated to the obtained amount of light. γ: represents an arbitrary coefficient, respectively. The gradation of the image according to claim 1, wherein the density characteristic curve is a photograph concentration characteristic curve indicating a correlation between the blackening degree (concentration D) of the photosensitive photosensitive material and the logarithmic value (log E) of the exposure amount (E). Transformation. An image according to claim 1, wherein in the scaling of the D (vertical) side-X (horizontal) axis of the DX rectangular coordinate system defining the density characteristic curve, the X-axis scale is equal to the D-axis scale. Gradation conversion method. The method according to claim 1, wherein the image information value X _n correlated with the light quantity is a normalized light quantity value when the [X _s -X _H ] value (dynamic range of the image information value correlated with the light quantity) is adjusted to 1.0. Gradation conversion method of image to be made.