JPH11331627A - Method for converting colorimetric value and device for outputting color image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct a colorimetric value to be the desired one by converting the colorimetric value into an image data value through the use of a first correspondence relation at the time of measuring an optional color by a first colorimeter and converting the converted image data value into the colorimetric value of the second colorimeter through the use of the second correspondence relation. SOLUTION: A color chart G' having plural color patches where the value of image data is changed is measured by the second colorimeter 22, the second correspondence relation between the colorimetric value and the image data value and three-dimensional CM-LUT 12 are obtained, the color chart G' is measured by the first colorimeter 21 and the first correspondence relation between the colorimetric value and the image data value and a colorimetric value correcting table 24 are obtained. When the optional color is measured by the first colorimeter 21, the colorimetric value is converted into the image data value through the use of the first correspondence relation and the table 24 and the converted image data value is converted into the colorimetric value of the second colorimeter 22 through the use of the second correspondence relation and three-dimensional CM-LUT 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a colorimetric value conversion method for converting a colorimetric value measured by a first colorimeter into a colorimetric value of a second colorimeter.

Further, the present invention relates to, for example, an input RGB
(Red, green, blue) based on image data, CMY (cyan,
Colors output by a color image output device that emits colors in three hues (magenta, yellow) are colorimetric values of a built-in colorimeter or externally on-line to correct so that colors output in a desired color are developed. The present invention relates to a color image output device which can correct a colorimetric value of a colorimeter connected by the above to a desired colorimetric value.

[0003]

2. Description of the Related Art For example, there is a color image output device such as a color printer which forms a color image by forming three color materials of CMY at predetermined gradations. FIG. 10 shows a schematic configuration of a color image output apparatus 1 of this type. In the color image output device 1, input image data (device-dependent image data) RGB of three hues are converted into one-dimensional LUTs (look-up tables) 2, 3 and 4 for gradation correction.
Are supplied to the exposure unit 6 after gradation conversion by the LUT 5 having

In the exposure section 6, laser diodes emitting R, G and B colors are driven according to output image data RGB of three hues after gradation correction by the one-dimensional LUTs 2, 3 and 4, and each laser diode is driven. A latent image is formed on the film F by irradiating the light L on the film F, and a predetermined developing process is performed on the film F on which the latent image is formed, whereby an image composed of three CMY hues as a visible image is formed. The formed film F can be obtained.

[0005] Such a color image output device 1 is used, for example, as a proofer (referred to as a printing proofer) for a color printing machine. The reason for using a color image output device as a proofer for printing is that before creating an actual color print using a color printing machine that uses a rotary press, etc.
This is to create a proof print on which a color image for proofing is formed (referred to as a color print proof). The printing proofer does not require the steps of a printing plate or the like required by a color printing machine. This is because a color print (a hard copy on which a color image is formed) can be easily created a plurality of times in a short time.

That is, by simulating the color of a color print produced by a color printing machine to be used from now on by proof printing of the color image output device 1, it is possible to easily confirm the color in a process prior to actual printing. Because.

By the way, this type of color image output device 1
, The gradation correction characteristics (gradation) of the one-dimensional LUTs 2, 3, and 4 (stored in the memory) which are incorporated in advance corresponding to standard printing conditions (conditions of ink, paper, and the printing press itself). However, the printing condition does not completely match with the printing condition (desired printing condition) of the printing press that the user is going to actually use. When trying to create
It becomes necessary to correct (correct) the gradation characteristics of the one-dimensional LUTs 2, 3, and 4 according to the desired printing conditions.

Therefore, for example, for the input image data RGB, the C
Target gradations (target density gradations) Dc0, Dm0, Dy as shown in FIG.
When set to 0, the input image data RG is output from the one-dimensional LUTs 2, 3, and 4 constituting the gradation correction LUT 5.
The gradation characteristics of the standard one-dimensional LUTs 2, 3, and 4 incorporated in advance in accordance with the standard printing conditions are corrected (corrected) so that B matches the target gradations Dc0, Dm0, and Dy0. There is a need.

In this case, according to the gradation correction method in the conventional color image output apparatus 1, first, as shown in the flowchart of FIG. 12, each of the image data R, G, and B constituting the input image data RGB is respectively processed to a predetermined level. Increase by key,
It is supplied to the exposure unit 6 through standard one-dimensional LUTs 2, 3, and 4 (incorporated in the color image output apparatus 1 from the beginning).
A single color patch of each Y color is output (step S1), and the densities Dc, Dm, and Dy of each single color patch are measured (step S1).
2).

Next, the measured densities Dc, Dm, Dy and the target gradations Dc0, Dm0, Dy0 shown in FIG. 11 are compared for each patch having a predetermined gradation, and a difference is output (step S3). Then, it is determined whether or not this difference is within a desired difference (step S4).

Since the printing conditions are to be changed, the determination in step S4 is normally negative, and the LUTs 2, 3, and 4 are trial and error according to the difference obtained in step S4.
The one-dimensional LUTs 2, 3, and 4 are corrected by correcting the correspondence (conversion relation) between each RGB value of the input image data RGB and each RGB value of the output image data RGB (step S5). . Below, correspondence (conversion)
For example, represents a relationship for converting an input image data value into an output image data value and a relationship for inversely converting an output image data value to an input image data value.

By repeating the processing from step S1 to step S5 until the determination in step S4 is established, the measured densities Dc, Dm, Dy and the target gradation Dc
One-dimensional LUTs 2, 3, and 4 after gradation correction in which 0, Dm0, and Dy0 are values within a desired range are obtained.

However, in the above-described gradation correction method in the conventional color image output apparatus 1, the one-dimensional LUT 2,
Correction (correction) of the gradation characteristic, which is the input / output correspondence of 3, 4
Is performed by trial and error, so that the one-dimensional L
Along with the correction of the UTs 2, 3, and 4, it is necessary to print out a single color patch again and repeat the work of measuring the density each time it is printed out. There is a problem that the determination of the correction amount on the basis of itself requires a high level of skill.

In order to solve this problem, the following method is considered. Since this technique is a new technique, it will be described in more detail in the following embodiments of the present invention, and will be briefly described here.

In this method, first, the condition that the output image data RGB of the color image output device 1 is R = G = B. In other words, the LUTs 2, 3, and 4 each have a so-called through (input-output relationship of 1). The target gradation (referred to as a target colorimetric value) is set so that the gray balance can be obtained in the state (1) of (1: 1 relationship). Next, a color chart having color patches in which the output image data RGB is evenly distributed is output from the color image output device 1, and each color patch is measured.
Look-up table for three-dimensional color matching (hereinafter, three-dimensional CM-L) for converting colorimetric values to RGB values
Also called UT. ) To create. Next, one-dimensional LUT
Using 2, 3, and 4, the input image data RGB
The color image output device 1 creates a gray chart under the condition of = G = B and measures the colors (measured colorimetric values). Then, R corresponding to the measured colorimetric value and the target colorimetric value, respectively.
The GB value is obtained by volume interpolation calculation with reference to the three-dimensional CM-LUT, and each difference between the obtained RGB values is calculated for each of the RGB values.
The correction of the one-dimensional RGB LUTs 2, 3, and 4 is completed by adding the LUTs 2, 3, and 4 to the one-dimensional LUTs 2, 3, and 4.

According to this method, the correction amounts (correction amounts) of the one-dimensional LUTs 2, 3, and 4 can be obtained mechanically rather than by trial and error. Accurate correction can be performed.

However, according to this method, the colorimeter (the first colorimeter to be corrected) incorporated in the color image output device 1 is used as the colorimeter for measuring the measured colorimetric values. ), And another colorimeter (a reference colorimeter, a second colorimeter) may be used to create the three-dimensional CM-LUT.

When creating a three-dimensional CM-LUT, it is necessary to measure an enormous amount of patches. Therefore, for example, in a manufacturer, a relatively large-sized patch capable of two-dimensional measurement (surface measurement) is used. An expensive colorimeter is used. On the other hand, for correction of the one-dimensional LUTs 2, 3, and 4, an inexpensive relatively small and spot-like measurement (point measurement) built in the color image output apparatus 1 is possible. This is because a simple colorimeter may be used. In this case, the three-dimensional CM-LUT created using the reference second colorimeter is stored in the memory of the color image output apparatus 1 having the first colorimeter to be corrected. That is, the user of the color image output apparatus 1 uses the built-in colorimeter to perform the one-dimensional LUT 2,
3 and 4 will be corrected.

However, in general, even if the same gray chart is measured, the colorimetric value differs for each colorimeter. Therefore, using the three-dimensional CM-LUT described above, a one-dimensional LUT
Even if the one-dimensional LUTs 2, 3, and 4 are modified so that the outputs of 2, 3, and 4 are converted to target RGB values,
Errors in colorimetric values between colorimeters, so-called errors due to model differences remain, and as a result, colors cannot be perfectly matched,
Even with the new method described above, the LUT
Correction by fine adjustment is required to intentionally shift the gradation characteristic, which is the correspondence relationship between the input and output of 2, 3, and 4, and the color output by the color image output device 1 by the fine adjustment is a desired color. It needs to be colored.

[0020]

SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and has been developed in consideration of a colorimeter built in a color image output device or a colorimeter connected online externally. Correction of three hues for adjusting the color output from the color image output device to a desired color even if the colorimeter used to create the three-dimensional CM-LUT is different. In order to make it possible to correct (correct) a one-dimensional LUT for a short time without performing fine correction, the colorimetric value measured by the first colorimeter is used by the second colorimeter. It is an object of the present invention to provide a colorimetric value conversion method capable of converting to a colorimetric value.

Further, the present invention provides, for example, an input RGB
(Red, green, blue) based on image data, CMY (cyan,
Colors output by a color image output device that emits colors in three hues (magenta, yellow) are colorimetric values of a built-in colorimeter or externally on-line to correct so that colors output in a desired color are developed. It is an object of the present invention to provide a color image output device which can correct a colorimetric value of a colorimeter connected by the above to a desired colorimetric value.

[0022]

In this section, for ease of understanding, description will be made with reference numerals in the accompanying drawings. Therefore, the contents described in this section should not be construed as being limited to those given the reference numerals.

In the colorimetric value conversion method according to the first aspect of the present invention, a color chart (G ') having a plurality of color patches in which image data values are changed is converted to a second colorimeter (2).
2) to obtain a second correspondence (12) between the colorimetric values and the image data values, and to measure the color chart (G ') by the first colorimeter (21). A first correspondence (24) between a color value and an image data value is obtained, and when an arbitrary color is measured by the first colorimeter, the measured value is converted to an image data value using the first correspondence. To
The converted image data values are converted into colorimetric values of the second colorimeter using the second correspondence.

In this case, the first correspondence is a look-up table for converting colorimetric values XYZ or L ^* a ^* b ^* into image data values RGB, and the second correspondence is image data values. RGB is measured by XYZ or L ^* a ^*
It is a lookup table for converting into b ^* (the invention according to claim 2).

According to a third aspect of the present invention, in the colorimetric value conversion method, the gray chart (G ″) is measured by the first colorimeter (21) under the condition that the gradation values of each hue of the image data are equal. Then, the measured reflectance is set to Rλ1, and the reflectance of the gray chart (30) in which the number of gray patches whose reflectance is constant irrespective of wavelength in the visible wavelength range is 1 or more is determined at a predetermined wavelength interval dλ in the visible wavelength range. , A second colorimeter (22) and the first colorimeter to measure the reflectance at predetermined wavelength intervals, and the first colorimetry with respect to the reflectance of the second colorimeter. The reflectance ratio of the meter is Kλ, the constant is k, and the color matching function is x
When λ, yλ, zλ, and the spectral value of the observation light source are Sλ,
With the integration range as the visible wavelength range, the colorimetric values XYZ are
Expression X = k∫ (xλ · Kλ · Rλ1 · Sλ) dλ Y = k∫ (yλ · Kλ · Rλ1 · Sλ) dλ Z = k∫ (zλ · Kλ · Rλ1 · Sλ) dλ XYZ or the colorimetric value XYZ
A colorimetric value converted into a colorimetric value L ^* a ^* b ^* in the LAB space is defined as a corrected colorimetric value of the first colorimeter.

According to a fourth aspect of the present invention, there is provided a color image output apparatus, comprising: a gradation conversion means (2, 2) for performing gradation conversion of input device-dependent image data so as to correspond to a desired printing condition of a printing press. 3, 4) to the exposure recording unit,
In a color image output apparatus for outputting a color print (G) such as a print proof from the exposure recording unit, a color chart (G ′) having a plurality of color patches having different values of the image data is output from the exposure recording unit. Output,
A color conversion means (12) for converting colorimetric values into device-dependent image data values created by measuring in advance by a second colorimeter (22), and measuring the color chart (G '). A first colorimeter (21) for obtaining a correspondence relationship with colorimetric values corresponding to the input device-dependent image data;
And a colorimetric value correcting means (24) for converting the colorimetric value of the first colorimeter into the colorimetric value of the second colorimeter so as to match the colorimetric value of the colorimeter. And an output of the colorimetric value correcting means (24) is supplied to the color converting means (12).
It is characterized in that the gradation conversion characteristics of (3) and (4) are corrected.

In this case, the output of the colorimetric value correcting means (24) is supplied to the color converting means (12), and the output of the color converting means is used to calculate the level of the gradation converting means (2, 3, 4). When correcting the tone conversion characteristics, the colorimetric values (L ^* 0a ^* 0b ^*) of the target gradation are set in advance so that the gray balance can be obtained under the condition that the hues of the image data supplied to the exposure recording unit are equal ^.
0) is set, and then a gray chart (G ″) is output from the exposure recording section under the condition that the respective hues of the input image data of the gradation conversion means are equal, and the output gray chart (G ″) is output. The first calorimeter measures the color, and the calorimetric value is corrected by the calorimetric value correcting means (24) to obtain a measured calorimetric value (L ^* a ^* b ^* ). The measured colorimetric values (L ^* a ^* b ^* ) and the respective colorimetric values (L
^* 0a ^* 0b ^* 0) is input to the color conversion means (12), and each hue corresponding to each colorimetric value (L ^* 0a ^* 0b ^* 0) of the target gradation output from the color conversion means. Image data values (R0, G0, B0) and the measured colorimetric values (L ^* a
^* b ^* ) for each hue image data value (R1, G1,
The gradation conversion characteristic is corrected by adding each difference (ΔR, ΔG, ΔB) of B1) to the output of the gradation conversion means of each hue. invention).

Further, in the invention according to claim 5, the output gray chart (G ") is measured by the first colorimeter, and the colorimetric values are corrected by the colorimetric value correcting means (24).
When the measured colorimetric value (L ^* a ^* b ^* ) corrected by the above is obtained, the colorimetric value correcting means (24) sets the number of gray patches having a constant reflectance of 1 or more in the visible wavelength range regardless of the wavelength. The reflectance of the gray chart (30) is measured at a predetermined wavelength interval dλ in the visible wavelength range with a reference colorimeter and the built-in colorimeter to determine the reflectance at a predetermined wavelength interval. The ratio of the reflectance of the first colorimeter to the reflectance of the second colorimeter is Kλ, the constant is k, and the color matching functions are xλ and y.
Assuming that λ, zλ, and the spectral value of the observation light source are Sλ, the colorimetric value XYZ is expressed by the formula X = k∫ (xλ · Kλ · Rλ1 · Sλ) dλ Y = k∫, where the integration range is the visible wavelength range. yλ · Kλ · Rλ1 · Sλ) dλ Z = k∫ (zλ · Kλ · Rλ1 · Sλ) dλ, and the colorimetric value XYZ or the colorimetric value XYZ is determined by CIE.
The value converted into the colorimetric value L ^* a ^* b ^* in the LAB space is created as correction means as a colorimetric value after correction of the first colorimeter, and the output gray chart (G ″) is generated. ) Is measured by the first colorimeter, the reflectance Rλ1 is measured at a predetermined wavelength interval in the visible wavelength range, the measured reflectance is input to the above equation, and the corrected measurement colorimetry is performed. Value (L ^* a
^* b ^* ) is obtained (the invention according to claim 6).

Further, according to the color image output apparatus of the present invention, there is provided a gradation conversion means for performing gradation conversion of input device-dependent image data so as to correspond to a desired printing condition of a printing press. 2, 3 and 4), to a color image output device capable of outputting a color print (G) such as a print proof from the exposure recording unit and measuring the color print. A color chart created by outputting a color chart (G ′) having a plurality of color patches in which the values of image data are changed from the exposure recording unit and measuring the color chart in advance by a second colorimeter (22). Color conversion means (12) for converting the values into device-dependent image data values; and colorimetric value correction means (24) for converting the output colorimetric values of the first colorimeter into the input colorimetric values of the color converting means. ), And the colorimetric value complement When creating the means, the reflectivity of a gray chart having a constant number of gray patches whose reflectance is constant irrespective of the wavelength in the visible wavelength range is 1 or more at the predetermined wavelength interval dλ in the visible wavelength range. Color meter and the first
Measure with a colorimeter to determine the reflectance at predetermined wavelength intervals,
The ratio of the reflectance of the first colorimeter to the reflectance of the second colorimeter is Kλ, the constant is k, and the color matching functions are xλ and y.
Assuming that λ, zλ, and the spectral value of the observation light source are Sλ, the colorimetric value XYZ is expressed by the formula X = k∫ (xλ · Kλ · Rλ1 · Sλ) dλ Y = k∫, where the integration range is the visible wavelength range. yλ · Kλ · Rλ1 · Sλ) dλ Z = k∫ (zλ · Kλ · Rλ1 · Sλ) dλ, and the colorimetric value XYZ or the colorimetric value XYZ is determined by CIE.
A colorimetric value converted into a colorimetric value L ^* a ^* b ^* in the LAB space is defined as a corrected colorimetric value of the first colorimeter.

According to the present invention, there is provided a color image output apparatus according to any one of claims 4 to 7, wherein
The first colorimeter 21A is connected to the color image output device externally on-line (the first colorimeter 21A: the invention according to claim 8).

Further, according to the present invention, in the color image output device according to any one of claims 4 to 7, the first colorimeter is built in the color image output device. (First colorimeter 21: invention according to claim 9).

[0032]

An embodiment of the present invention will be described below with reference to the drawings. In the drawings referred to below, the same reference numerals are given to those corresponding to those shown in FIGS.

FIG. 1 shows a schematic configuration of a color image output apparatus 10 such as a color printer to which the method of the present invention is applied. The color image output device 10 includes an exposure unit 6 that outputs R, G, and B laser beams L, respectively.
have. The donor film F cut into a predetermined length by an internal cutter (not shown) is transferred from the donor film F, which is a photosensitive material wound into a roll, to the exposure unit 6.

A dampening solution is applied to the donor film F on which a latent image has been formed by exposure recording by the laser beam L from the exposure unit 6, and the roll-shaped image receiving paper G is cut into a predetermined length. The image receiving papers G are opposed to each other and are attached to each other.

The bonded product is heated by a heating roller 8 in a heat developing / fixing unit, whereby the development proceeds.
The dye on the donor film F is transferred to and fixed on the receiving paper G,
The transfer of the image is completed. Thereafter, the used donor film F and the image receiving paper G are peeled off, and a high-quality color print (also denoted by a symbol G) on which an image Img having three hues of CMY is formed is completed.

In this case, the image Im on the color print G
g corresponds to three-color image data RGB (device-dependent image data) supplied to the exposure unit 6 from a look-up table (LUT) 5 as a gradation correction unit. The image data RGB supplied to the input side of the exposure unit 6 are LUT2, which are LUTs as one-dimensional gradation correction means (one-dimensional conversion tables) created in advance based on standard printing conditions. The input image data RGB (device-dependent image data) of three hues are converted data according to 3 and 4.

In the color image output device 10 configured as described above, as described above, the color image output device 1
A proof (proof print) is created under printing conditions (also called desired printing conditions or target printing conditions) different from the printing conditions (standard printing conditions) of the LUTs 2, 3, and 4 stored in the memory 0. In such a case, a standard LUT 2 (stored in a memory) previously incorporated in the color image output device 10 so as to conform to the target printing condition,
It is necessary to correct (correct) the gradation characteristics of 3 and 4.

A colorimeter (for measuring the colorimetric value of the image Img formed on the color print G for determining the correction amount (correction amount) of the gradation characteristics of the LUTs 2, 3, and 4) Hereinafter, it is also referred to as a first colorimeter to be corrected.) 21 is integrally incorporated in the color image output device 10. The first colorimeter 21 may be configured to be connected online as the first colorimeter 21A to the outside of the image output device 10 via the connector 23 instead of being built-in (FIG. 2). reference).

In this embodiment, the exposure unit 6
In such a case, a portion including a portion where the color print G is formed by exposing the donor film F may be included. When the portion including the portion for forming the color print G is included, the portion is also referred to as an exposure recording portion.

FIG. 2 shows the first colorimeter 21 to be corrected incorporated in the color image output device 10 or the first colorimeter 21A connected online to the outside and the color image output device 10 offline. A colorimetric value correction table (colorimetric value correction means, colorimeter) for correcting a measurement difference (model difference) with a colorimeter (hereinafter also referred to as a second colorimeter) 22 as a reference FIG. 1 is a block diagram of a color image output apparatus 10 according to this embodiment in which a value conversion table or a colorimetric value conversion unit 24 is mounted (stored in a memory).

In the color image output device 10, a three-dimensional color matching LUT (three-dimensional CM-LUT) 12 which has a second correspondence and functions as a color conversion means is mounted in a memory.

After the procedure for creating the three-dimensional CM-LUT 12 is described below, the procedure for creating the colorimetric value correction table 24 which is the first correspondence and functions as colorimetric value correction means will be described. A procedure for correcting (correcting) the one-dimensional LUTs 2, 3, and 4 using the dimensional CM-LUT 12 and the colorimetric value correction table 24 will be described.

First, the procedure for creating the three-dimensional CM-LUT 12 will be described with reference to the flowchart of FIG.

In this case, as shown in FIG. 4, a target gradation (target density gradation) Dt corresponding to a target printing condition corresponding to a color printing machine to be actually used is determined (step S11). . Here, the target gradation Dt is the output image data RGB (in the following description, the output image data RGB means the image data output from the LUTs 2, 3, and 4, and the input image data RGB
Means image data input to the one-dimensional LUTs 2, 3, and 4. ) Are set so that gray balance can be obtained on the color image output device 10 under the condition (R = G = B) that each RGB value (gradation value of each RGB hue) is equal, and for example, colorimetry in the CIELAB space The value (target colorimetric value) is represented by L ^* 0a ^* 0b ^* 0.

The correspondence between the colorimetric values and the density values can be determined, for example, by measuring a plurality of patches having different densities using a colorimeter and a densitometer, respectively. Then, a density value for an arbitrary colorimetric value L ^* a ^* b ^* can be obtained by volume interpolation.

The target gradation Dt is actually measured, for example, by measuring the relationship between the dot% value and the density of a printed matter of a color printing machine from which a proof is to be created, and converting the dot% value into output image data RGB values. Can be obtained. In the target gradation Dt shown in FIG. 4, the density value exists when the value of the output image data RGB is in the vicinity of R = G = B = 0 because of the paper color of the printed matter (the ground color of the actual printing paper). is there.

Next, in order to create a three-dimensional CM-LUT 12 representing the correspondence between the output colorimetric values of the color image output device 10 and the respective RGB values of the output image data RGB, first, the one-dimensional LUTs 2, 3,. 4 is a so-called through state (a 1: 1 relationship between input and output), and a color chart G 'which is a color print G having color patches in which the values of the respective hues of the output image data RGB are evenly distributed. (See FIG. 2) is output (step S12). For example, when the gradation value of each RGB hue of the output image data RGB is an 8-bit gradation that takes a value of 0 to 255,
Each 9 steps and the value for each of the RGB colors is changed evenly every gradation width 3 ^3, and outputs a color chart G 'having a total of 9 ³ = 729 color patches. At this time, R = G =
In the vicinity of gray B, a color chart having a color patch whose number of divisions is doubled is output. This is because in the vicinity of gray where human visual discrimination is excellent, the interpolation grid is made finer, and the conversion accuracy of the three-dimensional CM-LUT 12 representing the correspondence between output colorimetric values and output image data RGB is increased.

Next, each color patch of the output color chart G 'is measured by the second colorimeter 22 as a reference (step S13), and for each color patch, RGB of each hue of the output image data RGB. A three-dimensional CM-LUT 12 representing the conversion relationship between the value and the colorimetric value L ^* a ^* b ^* is created (step S14).

[0049] Figure 5 is a three-dimensional CM-LU expressed omitted manner as 5 ^three combined since the complexity of 9 ^three combinations
9 shows a configuration of a measurement grid point of T12. The measurement grid point indicated by a small circle is the second colorimeter 2 that is actually used as a reference.
This corresponds to a point having the colorimetric values L ^* a ^* b ^* measured by the method 2. As described above, in the vicinity of R = G = B,
Since the grid points (measured points) are measured finely,
In the cube representing the three-dimensional CM-LUT 12 shown in FIG. 5, each cubic grid including a line connecting the origin O of the RGB coordinates and the vertex V farthest from the origin O has finer grid points. For example, if the description is made in a planar manner using the image data R and the image data B, as shown schematically in FIG. The colorimetric values L ^* a ^* b ^* are measured. As described above, the three-dimensional CM-L representing the correspondence between the colorimetric values obtained by the reference second colorimeter 22 and the output image data RGB.
The UT 12 can be created.

Next, the first colorimeters 21, 21 to be corrected are
A procedure for creating the colorimetric value correction table 24 for matching the colorimetric value of A with the colorimetric value of the second colorimeter 22 as a reference will be described.

In this case, first, as shown in FIG.
In the visible wavelength range from 0 nm to 780 nm, the reflectance Rf is constant irrespective of the wavelength, and the gray chart 30 having several (six in this embodiment) gray patches from the vicinity of highlight to the vicinity of solid is prepared. (Step S1
5).

Next, a first colorimeter (for example, a spectral reflection type colorimeter) 21 and 21A to be corrected and a reference second colorimeter (similarly, a spectral reflection type colorimeter) According to 22, the reflectance of the gray patch constituting the gray chart 30 is measured at a predetermined wavelength interval (dλ, in this embodiment, dλ = 20 nm) in the visible wavelength range (step S16). First colorimeter 2 to be corrected
Assuming that the reflectance measured by the first and second colorimeters 22 is Rλ1 ′ and the reflectance measured by the reference second colorimeter 22 is Rλ2, as shown in FIG. (This represents the relationship between the reflectance of the first colorimeters 21 and 21A to be corrected in the visible wavelength range and the reflectance of the reference second colorimeter 22.) 32 is obtained.

Next, with reference to the reflectance measurement tables 32 for the number of gray patches, the ratio of the measured reflectance for each predetermined wavelength interval dλ (also referred to as a colorimeter correction value) Kλ (Kλ = Rλ)
2 / Rλ1 ′) (referred to as a one-dimensional reflectance ratio table) 34 is obtained (step S17). In this embodiment, the predetermined wavelength interval dλ is set to dλ = 20.
nm, the number of reflectance ratio tables 34 obtained is 21 {(780-380) / 20 + 1 = 21}.
become.

Next, in view of chromaticity, the standardization coefficient, which is a constant, is k, the colorimeter correction value is Kλ, and the color matching function is x.
λ, yλ, zλ, and when the spectral value of the observation light source when observing the printed sample such as the color chart G ′ and the gray chart 30 is Sλ, the colorimetric value XYZ is obtained by the following equation (1). Note that, in equation (1), R
λ1 (described later) is the first colorimeter 21, 2 to be corrected.
1A shows the reflectance when a predetermined gray chart described later is measured. The integral range in the equation (1) is 3
It is 80 nm to 780 nm.

X = k∫ (xλ · Kλ · Rλ1 · Sλ) dλ Y = k∫ (yλ · Kλ · Rλ1 · Sλ) dλ Z = k∫ (zλ · Kλ · Rλ1 · Sλ) dλ (1) Each of the colorimetric values XYZ can be mathematically converted into a colorimetric value L ^* a ^* b ^* in the CIELAB space mathematically in terms of chromaticity. Equation (1) and colorimetric value L of colorimetric value XYZ
^As shown in FIG. 2, the second colorimeter 22 based on the measured reflectance Rλ1, which is the output value of the first colorimeter 21, 21A to be corrected, according to the correspondence to ^* a ^* b ^* . A colorimetric value correction table 24 that can be converted (converted, corrected) into the above colorimetric values L ^* a ^* b ^* can be created (step S18).

As described above, the measured value of the first colorimeter 21 or the first colorimeter 21A to be corrected can be converted into the measured value of the second colorimeter 22 as a reference. A colorimetric value correction table 24 is obtained (step S18).

Next, using the three-dimensional CM-LUT 12 created in step S14 and the colorimetric value correction table 24 created in step S18, one-dimensional LUTs 2, 3, and 4 are used.
The procedure for correcting (correcting) is described.

In this case, first, the RG before the correction (correction) in which the gray balance is adjusted under the standard printing conditions.
Using the one-dimensional LUTs 2, 3, and 4 for each of the B hues, the condition that the values of each hue of the input image data RGB are equal (R = G =
In B), a gray chart {R} that is a color print G when the RGB values are simultaneously changed in, for example, 17 steps.
A chart {G} (see FIG. 2) on which a gray scale is formed including the ground color of the color print G of = G = B = 0 is output from the color image output device 10 (step S1).
9).

Next, this gray chart G ″ is expressed by
First colorimeters 21, 21 to be corrected for each combination of G = B
A, a wavelength of 380 nm to 780 nm, a wavelength of 20
The reflectance Rλ1 is measured at nm intervals, and is converted into a reference colorimetric value of the second colorimeter 22 using the colorimetric value correction table 24. The conversion (conversion) process of the colorimetric value will be described in more detail. The measured reflectance Rλ1 is substituted into the above equation (1) to obtain a colorimetric value XYZ.
Z is converted into a colorimetric value (referred to as a measured colorimetric value) L ^* a ^* b ^* in the CIELAB space (step S20).

Next, as shown in FIG. 8, each R = G
= Measured colorimetric value L for each combination of B^*a ^*b^*And step S
The colorimetric value L of the target gradation determined in 11^*0a^*0b^*0 and
Are compared (step S21). In FIG. 8,
The characteristic indicated by the symbol Dt corresponds to the target gradation (target darkness) shown in FIG.
(Dot gradation) Dt.

The colorimetric values L ^* 0a ^* 0b ^* 0 of this target gradation
And the measured colorimetric values L ^* a ^* b ^* and of the difference ΔL ^* Δa ^* Δb ^*
Is determined by comparing whether or not is within a desired range (step S22). If the printing conditions have changed, the first determination is not made.

Therefore, the third order obtained in step S14
Using the original CM-LUT 12, the colorimetric value L of the target gradation^*
0a^*0b^*RGB values of output image data corresponding to 0
And the measured colorimetric value L^*a^*b^*Output image data corresponding to
(Step S23).
The difference between the obtained RGB values is obtained (step S24). this
In case, each RGB value refers to the three-dimensional CM-LUT12
And the colorimetric value L of the target gradation ^*0a^*0b^*0 and measurement
Color value L^*a^*b^*Interpolation grid (cubic grid) surrounding each
And calculate the RGB values of each grid point constituting the interpolation grid.
Read out, as shown in FIG. 9, consisting of a computer etc.
The target gradation is obtained by the volume interpolation calculation by the volume interpolation processing unit 14.
Colorimetric value L^*0a^*0b^*0 and measured colorimetric value L^*a^*
b^*The RGB values of the three hues corresponding to
Can be. Here, the colorimetric value L of the target gradation is^*0a^*0b
^*The RGB value obtained corresponding to 0 is defined as R0G0B0 and measured.
Constant color value L^*a^*b^*The RGB value obtained in correspondence with
When G1B1 is set, the difference between the RGB values is shown in FIG.
In the difference generation unit 15, ΔR (= R0−R1), ΔG
(= G0-G1) and ΔB (= B0-B1)
Can be.

Next, the LUTs 2, 3, and 4 are corrected (corrected) based on the difference ΔRΔGΔB (step S25). This correction calculation is quite simple,
The difference ΔRΔGΔB is calculated by using the current LUT
What is necessary is just to add to the correction amounts of 2, 3, and 4, respectively. More specifically, for example, based on the R value, as shown in FIG. 2, the input image data R is converted into output image data R1 by an LUT2 which is a previously determined gradation correction means, When the image data R1 is the colorimetric value L ^* 0 of the target gradation
Since it is preferable that the image data is converted into image data R0 corresponding to a ^* 0b ^* 0, the addition means 1 is used as a correction amount (correction value).
6, a new LUT 2 ′ obtained by adding the difference ΔR (= R 0 −R 1) only needs to be replaced with the LUT 2 shown in FIG.

As described above, the one-dimensional LUTs 2, 3, and 4 are converted into the one-dimensional LUT
The colorimetric values 2, 3, and 4 are used as the colorimetric values L ^* 0a ^* 0b of the target gradation.
LUT2 '(LUT2 and addition means 16) and LUT3' (LUT3 and addition means 17) that can be converted to ^* 0
And LUT 4 '(LUT 4 and adding means 18), so that the LUT
2, 3, 4 accurate corrections can be made in a very short time.

According to the above-described embodiment, the first colorimeters 21 and 21A to be corrected and the second colorimeter 22 serving as a reference are corrected.
Is the first correction target even if there is a measurement difference between
By installing a colorimetric value correction table 24 capable of converting the measured values of the colorimeters 21 and 21A into the measured values of the second colorimeter 22 as a reference, the color image output device 10 The effect of being able to manage colors based on the colorimetric values used in the three-dimensional CM-LUT 12 is achieved.

In the above-described embodiment, the reflectance Rλ1 is set as the colorimetric value L ^* as the colorimetric value correction table 24 ^.
Although a table for converting into a ^* b ^* is used, the present invention is not limited to this, and the measurement of the second colorimeter 22 that directly serves as a reference for the measurement values of the first colorimeters 21 and 21A to be corrected is used. A table for converting to a value may be used. In this case, RG of the output image data RGB used in step S12 described above is used.
B. A color chart G ', which is a color print G having a color patch composed of a combination in which the values of the respective hues are uniformly changed, is measured by a reference second colorimeter 22, and the colorimetric values L ^{* are} measured ^. The reference correspondence between the a ^* b ^* and the output image data RGB (three-dimensional CM-LUT 12) is obtained, and the color chart G 'is measured by the first colorimeters 21 and 21A to be corrected for colorimetry. The correspondence (three-dimensional LUT) of the correction target between the value L ^* a ^* b ^* and the output image data RGB is obtained.

In this way, when an arbitrary color is measured by the first colorimeters 21 and 21A to be corrected, the colorimetric values L ^* a ^* b ^* are set to correspond to the correction target (corresponding to the correction target). 3
The corresponding image data RGB is obtained by using a volume LUT) and volume interpolation processing, and the image data RGB is used as an input value of the reference correspondence (three-dimensional CM-LUT 12), and a corresponding colorimetric value L ^* a. ^* b ^{* is obtained} by volume interpolation calculation. The calculated colorimetric values L ^* a ^* b ^* are the colorimetric values L measured by the first colorimeters 21 and 21A to be corrected.
^* a ^* b ^* is the reference colorimetric value L of the second colorimeter 22
It is a value converted to ^* a ^* b ^* .

It should be noted that the present invention is not limited to the above-described embodiment, but can adopt various configurations without departing from the gist of the present invention.

[0069]

As described above, according to the present invention, the correspondence between the values measured by the first colorimeter and the values measured by the second colorimeter (the same color chart is used for the second colorimeter). The measurement is performed by the color meter and the first colorimeter, and the correspondence between each color of the color chart and each colorimeter) is prepared. Therefore, the first colorimetry is performed using the correspondence of each colorimeter. The colorimetric value measured by the meter can be easily (mechanically calculated) converted to the colorimetric value of the second colorimeter.

According to the present invention, a colorimeter built in a color image output device or a colorimeter connected online and externally is used to create a three-dimensional CM-LUT. Even if the total is different,
Since the measurement difference between the colorimeters is corrected, a one-dimensional LUT for correcting three hues for adjusting the color output from the color image output device so as to generate a desired color is provided.
Correction (correction) can be performed in a short time without performing correction by fine adjustment based on expert knowledge.

Therefore, the measured values output by the colorimeter built in the color image output device for performing the gradation correction or the colorimeter connected online on the outside and the three-dimensional values for performing color matching. Since the colorimetric values of the CM-LUT match, the colors match the colors defined in the three-dimensional CM-LUT for performing gradation correction, and stable color reproducibility can be obtained.

According to the present invention, a gray chart having a constant reflectance without depending on the wavelength in the visible wavelength range is measured by the first colorimeter and measured by the second colorimeter in advance. The corresponding relationship of the reflectance is determined as Kλ for each predetermined wavelength interval (dλ) in the visible wavelength range. Next, when the reflectance of an arbitrary color measured by the first colorimeter is Rλ1, the constant is k, the color matching functions are xλ, yλ, zλ, and the spectral value of the observation light source is Sλ, the integration range is as described above. As the visible wavelength range,
The colorimetric value XYZ is expressed by the formula X = k∫ (xλ · Kλ · Rλ1 · Sλ) dλ Y = k∫ (yλ · Kλ · Rλ1 · Sλ) dλ Z = k∫ (zλ · Kλ · Rλ1 · Sλ) dλ The colorimetric value XYZ or the colorimetric value XYZ is
The value converted into the colorimetric value L ^* a ^* b ^* in the LAB space is set as the corrected colorimetric value of the first colorimeter.
Therefore, the corrected colorimetric value matches the colorimetric value of the second colorimeter.

The first colorimeter built in the color image output device or the first colorimeter connected online
In order to convert the output colorimetric value of the colorimeter based on the output value of the second colorimeter as a reference, a first colorimeter built in the color image output device or an external The relationship between the reflectance of the first colorimeter and the reflectance of the second colorimeter connected online is determined, and this relationship is used to connect online to the first colorimeter built in the color image output device or to the outside. What is necessary is just to correct so that the reflectance of the first colorimeter becomes the reflectance of the second colorimeter. When the reflectance relationship is not used, the first colorimeter built in the color image output device or a color chart having a color patch composed of a combination of output image data substantially uniformly changed for each hue or It is measured by a first colorimeter externally connected online and measured by a reference colorimeter, and the first colorimeter built in the color image output device of the output image data or online externally. The correspondence between the colorimetric value of the connected first colorimeter and the colorimetric value of the reference colorimeter may be obtained in advance.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing an overall configuration of a color image output device to which an embodiment of the present invention is applied.

FIG. 2 is a block diagram of a color image output device used for explaining a procedure for correcting a one-dimensional LUT.

FIG. 3 is a flowchart for explaining an embodiment of the present invention;

FIG. 4 is a diagram showing a target gradation.

FIG. 5 is a three-dimensional CM for changing a colorimetric value to an RGB value.
It is a schematic diagram of -LUT.

FIG. 6 is an explanatory diagram showing an example in which a division grid interval is small in the vicinity of gray of a three-dimensional CM-LUT.

FIG. 7 is an explanatory diagram provided for obtaining a ratio of reflectance measured by a first colorimeter (colorimeter to be corrected) and a second colorimeter (reference colorimeter). .

FIG. 8 is a diagram illustrating a difference between a measured colorimetric value after a change in output conditions and a target gradation.

FIG. 9 is a diagram provided for describing a method of using a three-dimensional LUT.

FIG. 10 is a block diagram provided for explaining a conventional technique.

FIG. 11 is a diagram provided for describing a correction process according to the prior art for a one-dimensional LUT.

FIG. 12 is a flowchart provided to explain a correction process according to the prior art for a one-dimensional LUT.

[Explanation of symbols]

1, 10 ... color image output device 2, 3, 4 ... one-dimensional LUT for gradation correction 6 ... exposure unit 12 ... three-dimensional CM-LUT (second correspondence, color conversion means) 21, 21A ... first Colorimeter 22 ... second colorimeter 24 ... colorimetric value correction table (first correspondence, colorimetric value correction means) 30, G "... gray chart 32 ... reflectance measurement table 34 ... reflectance ratio Table G: Color print (receiving paper) G ': Color chart

Claims (9)

[Claims] 1. A color chart having a plurality of color patches in which image data values are changed is measured by a second colorimeter to obtain a second correspondence between colorimetric values and image data values. At the same time, the color chart is measured by a first colorimeter to obtain a first correspondence between a colorimetric value and an image data value. When an arbitrary color is measured by the first colorimeter, the measurement is performed. Converting values into image data values using the first correspondence, and converting the converted image data values into colorimetric values of the second colorimeter using the second correspondence. A colorimetric value conversion method characterized by the following. 2. The colorimetric value conversion method according to claim 1, wherein the first correspondence is a colorimetric value XYZ or L ^* a ^* b.
^* Is a look-up table that converts ^* to image data values RGB, wherein the second correspondence is image data values RGB
Is a look-up table for converting a colorimetric value into a colorimetric value XYZ or L ^* a ^* b ^* . 3. A gray chart under the condition that tone values of respective hues of image data are equal by a first colorimeter, and the measured reflectance is Rλ1, and the reflectance is irrespective of wavelength in a visible wavelength range. The reflectance of a gray chart having a constant number of gray patches of 1 or more is measured by a second colorimeter and the first colorimeter at a predetermined wavelength interval dλ in the visible wavelength range, and a predetermined wavelength interval is measured. , The ratio of the reflectance of the first colorimeter to the reflectance of the second colorimeter is Kλ, the constant is k, and the color matching function is x
When λ, yλ, zλ, and the spectral value of the observation light source are Sλ,
With the integration range as the visible wavelength range, the colorimetric values XYZ are
Expression X = k∫ (xλ · Kλ · Rλ1 · Sλ) dλ Y = k∫ (yλ · Kλ · Rλ1 · Sλ) dλ Z = k∫ (zλ · Kλ · Rλ1 · Sλ) dλ XYZ or the colorimetric value XYZ
A colorimetric value conversion method, wherein a value converted into a colorimetric value L ^* a ^* b ^* in a LAB space is used as a colorimetric value after correction by the first colorimeter. 4. An input device-dependent image data,
A color image output device that supplies a color print such as a print proof to the exposure recording unit through a gradation conversion unit that performs gradation conversion so as to correspond to a printing condition of a desired printing press; A color chart having a plurality of color patches in which data values are changed is output from the exposure recording unit, and a colorimetric value created by measuring in advance by a second colorimeter is used as a device-dependent image data value. A first colorimeter for measuring the color chart and obtaining a correspondence with a colorimetric value corresponding to the input device-dependent image data; and a first colorimeter. The colorimetric value of the first colorimeter is converted to the colorimetric value of the second colorimeter so that the colorimetric value of the colorimeter matches the colorimetric value of the second colorimeter. Colorimetric value correction means The output of the colorimetric value correction means is supplied to the color conversion means,
A color image output device, wherein the gradation conversion characteristic of the gradation conversion means is corrected by the output of the color conversion means. 5. The color image output device according to claim 4, wherein an output of said colorimetric value correction means is supplied to said color conversion means,
When correcting the gradation conversion characteristic of the gradation conversion means by the output of the color conversion means, a target gradation is set in advance so that a gray balance can be obtained under the condition that each hue of image data supplied to the exposure recording unit is equal. Next, a gray chart is output from the exposure recording unit under the condition that the respective hues of the input image data of the gradation conversion means are equal, and the output gray chart is subjected to the first measurement. Colorimetry is performed by a color meter, and the measured colorimetric value is corrected by the colorimetric value correcting unit to obtain a measured colorimetric value.Next, the corrected measured colorimetric value and each colorimetric value of the target gradation are calculated. Is input to the color conversion means, and the image data value of each hue corresponding to each colorimetric value of the target gradation and the image data value of each hue corresponding to the measured colorimetric value output from the color conversion means. The difference is output from the gradation converting means of each hue. A color image output device for correcting the gradation conversion characteristic by adding 6. A color image output apparatus according to claim 5, wherein said output gray chart is measured by said first colorimeter, and said colorimetric value is corrected by said colorimetric value correcting means. When obtaining a color value, the colorimetric value correction unit is configured to calculate the reflectance of a gray chart having a constant number of gray patches of 1 or more regardless of the wavelength in the visible wavelength range by a predetermined wavelength interval dλ for the visible wavelength range. Then, the reflectance at a predetermined wavelength interval is determined by measuring with a reference colorimeter and the built-in colorimeter, and the reflectance of the first colorimeter with respect to the reflectance of the second colorimeter. Is defined as Kλ, the constant is k, and the color matching function is x
When λ, yλ, zλ, and the spectral value of the observation light source are Sλ,
With the integration range as the visible wavelength range, the colorimetric values XYZ are
Expression X = k∫ (xλ · Kλ · Rλ1 · Sλ) dλ Y = k∫ (yλ · Kλ · Rλ1 · Sλ) dλ Z = k∫ (zλ · Kλ · Rλ1 · Sλ) dλ XYZ or the colorimetric value XYZ
A value converted into a colorimetric value in the LAB space is created as a correction unit that is used as a colorimetric value after correction by the first colorimeter, and the output gray chart is generated by the first colorimeter. Colorimetrically, measuring the reflectance Rλ1 at predetermined wavelength intervals in the visible wavelength range, inputting the measured reflectance to the above equation,
A color image output device for obtaining the corrected measured colorimetric value. 7. The device-dependent image data to be input,
It is supplied to an exposure recording unit through a gradation conversion unit that performs gradation conversion so as to correspond to the printing conditions of a desired printing press, and a color print such as a print proof is output from the exposure recording unit, and the color print is measured. A color image output device capable of outputting a color chart having a plurality of color patches in which the value of the image data is changed from the exposure recording unit, and is prepared by previously measuring with a second colorimeter. A color conversion unit for converting a colorimetric value into a device-dependent image data value; a colorimetric value correcting unit for converting an output colorimetric value of the first colorimeter into an input colorimetric value of the color converting unit; When the colorimetric value correction means is created, the reflectance of a gray chart in which the number of gray patches whose reflectance is constant regardless of wavelength in the visible wavelength range is 1 or more is set to a predetermined wavelength for the visible wavelength range. Interval dλ , Wherein the second colorimeter measured at the first colorimeter, determine the reflectance at a predetermined wavelength interval, the first for the reflectance of the second colorimeter
When the reflectance ratio of the colorimeter is Kλ, the constant is k, the color matching functions are xλ, yλ, zλ, and the spectral value of the observation light source is Sλ, the integration range is the visible wavelength range, and the colorimetric values are XYZ
X = k∫ (xλ · Kλ · Rλ1 · Sλ) dλ Y = k∫ (yλ · Kλ · Rλ1 · Sλ) dλ Z = k∫ (zλ · Kλ · Rλ1 · Sλ) dλ The color value XYZ or the colorimetric value XYZ is
A color image output device wherein a value converted into a colorimetric value L ^* a ^* b ^* in a LAB space is used as a colorimetric value after correction by the first colorimeter. 8. The color image output device according to claim 4, wherein said first colorimeter is externally connected to said color image output device online. A color image output device. 9. The color image output device according to claim 4, wherein said first colorimeter is built in said color image output device. Output device.