JPH1065930A - Color image processing method and color image processing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simulate observation of a color of a hard copy image on a display device so that a color of a displayed image is in matching with a color of a hard copy image observed actually under an environment estimated for observation even when the environment for the display device to be installed is a general and unlimited lighting condition or the environment for the hard copy estimated for its observation is under any lighting condition. SOLUTION: An equipment environment light recognition process 20 recognizes an installation lighting condition being a lighting condition under the environment where a color display device is installed. An observation environment light information recognition process 30 recognizes an observation lighting condition being a lighting condition under the environment estimated for observation of a color hard copy entered by the user. An environment light information correction process 40 decides a color conversion coefficient based on the installed lighting condition and the observation lighting condition. An image data conversion process 70 converts received image data into display use image data based on the color conversion coefficient from the environment light information correction process 40.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image processing method and a color image processing apparatus used for adjusting and checking the image quality of an image output as a color hard copy on a color display.

[0002]

2. Description of the Related Art In the field of printing and desktop publishing (DTP), a system for adjusting and checking the quality of a final output image on a display, so-called soft proof system, in order to speed up color proofing and reduce costs. Has been considered and is being put to practical use.

However, this soft proof system is
Conventionally, it is basically assumed that the display is installed under a certain lighting condition, and the final output image is also observed under the certain lighting condition.

[0004] Thus, the user can use the system in its limited installation environment, or otherwise make iterative adjustments based on heuristics without relying on the image on the display to achieve the desired image quality. Must obtain the final output image. Further, when the finally output hard copy is observed in an environment different from the environment assumed by the system, a desired image quality cannot be obtained as a result.

On the other hand, an illumination condition or ambient light in an environment where a display is installed (hereinafter referred to as an installation illumination condition or installation environment light) is detected to correct an image output on the display. It is thought that.

[0006] Specifically, Japanese Patent Application Laid-Open No. H4-255025 discloses that color correction of an image output on a display is performed based on a spectral spectrum obtained by a sensor or an external light table. Also, Japanese Patent Application Laid-Open No. 7-20
No. 3478 discloses that a white point (hereinafter, referred to as a white point) on a color display is automatically and colorimetrically matched to a white point of installation environment light.

On the other hand, it has also been considered to consider the chromatic adaptation effect to lighting conditions or ambient light in an environment where a hard copy is expected to be observed (hereinafter referred to as viewing illumination conditions or viewing environment light).

[0008] Specifically, Japanese Patent Application Laid-Open No. 5-216452 discloses that an image area and a non-image area on a display can be observed under various observation environments by measuring the spectral content of the observation environment with a sensor. It has been shown to convert the appearance of the case to look and to allow a preview of the printed matter. Also, Japanese Patent Application Laid-Open No. 7-105375 discloses that colors for adjusting adaptation are displayed around a display image, assuming an observation environment.

[0009]

However, Japanese Patent Application Laid-Open No. H4-255025 does not show a specific solution to the change in the apparent color of an image on a display due to ambient light. Moreover, no consideration is given to the case where the finally output hard copy is observed in an observation environment different from the assumed observation environment.

In the method disclosed in Japanese Patent Application Laid-Open No. 7-203478, when the installation environment light has a low color temperature of about 4100K to 4300K as in a general office, the white point on the color display is measured colorimetrically. Even if the white point of the installation environment light is matched, there is a problem that the color does not look the same as it looks. Therefore, simply adjusting the color on the display to the installation environment light cannot solve such a problem.

Japanese Patent Application Laid-Open No. Hei 5-216452 is based on the premise that the display is not affected by the installation environment light but is affected only by the color temperature of the white point on the display. Not considered.
Further, although the method of Japanese Patent Application Laid-Open No. 7-105375 takes measures against the chromatic adaptation effect, it does not have a mechanism for feeding back the installation environment light, and therefore cannot cope with a change in the installation environment light.

[0012] After all, the soft proof system considered so far has a display installation environment,
It can be used only in very limited cases, such as with a hood in a dark room or a bright room.

Further, as a soft proof system,
In addition to being able to simulate the color finish of the hardcopy image on the display, for example, to edit the display image with the hardcopy as the original, compare the display image and the hardcopy image simultaneously under the display installation environment Hopefully you can. However, for the above-mentioned reasons, this is difficult with the conventional method.

Therefore, the present invention provides a method for predicting that a hard copy is observed even when the environment in which the display is installed is not under specific restricted lighting conditions but under general unrestricted lighting conditions. Under any lighting conditions, the color of the display image should be hard-copy so that the impression matches the color of the hard-copy image actually observed in the environment expected to be observed. In addition to being able to simulate the finished color of an image on a display, it is also possible to simultaneously compare a display image and a hard copy image in an environment where the display is installed.

[0015]

According to the present invention, as a color image processing method, a first method for recognizing an installation illumination condition, which is an illumination condition in an environment where a color display is installed, is provided.
And a second step of recognizing an input observation illumination condition, which is an illumination condition in an environment in which a color hard copy is predicted to be observed, before or after the recognition of the installation illumination condition in the first step; A third step of determining a color conversion coefficient based on the installation illumination condition recognized in the first step and the observation illumination condition recognized in the second step; and a color conversion determined in the third step. A fourth step of converting the input image data into display image data based on the coefficient.

[0016]

In the color image processing method of the present invention having the above-mentioned structure, in the first step, the installation environment light information of the color display is taken in and recognized.
In the second step, the observation environment light information of the color hard copy is captured and recognized by the input by the user, and based on the installation environment light information and the observation environment light information recognized in the first step and the second step, In the third step, as a color conversion coefficient for converting the input image data into display image data, a color conversion coefficient suitable for the installation environment of the color display and suitable for the observation environment of the color hard copy is obtained. In four steps, the input image data is converted into display image data by the color conversion coefficient.

Therefore, even if the environment in which the display is installed is under general unrestricted lighting conditions,
In any environment where the hard copy is expected to be observed, the color of the display image is changed to the color of the hard copy image actually observed in the environment where the hard copy is expected to be observed. To match, the color appearance of the hardcopy image can be simulated on the display. Further, even when the display image and the hard copy image are compared at the same time under the installation environment of the display, the appearance impression of both can be matched.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] FIG. 1 shows an example of a color image processing system for realizing the color image processing method of the present invention.
This system includes a color display 1, a sensor 2, an input unit 3, and a color image processing device 10.

The sensor 2 is provided in the vicinity of the color display 1 and detects an illumination condition of an environment in which the color display 1 is installed. The detection output is a color image processing apparatus 10 as installation environment light information. It is taken in. The input means 3 includes a keyboard, a mouse, and the like, and is used for inputting lighting conditions of an environment in which a user is expected to observe a hard copy. The lighting conditions input from now on are based on color image processing as viewing environment light information. Apparatus 1
It is taken into 0.

The color image processing apparatus 10 is constituted by, for example, a computer, and the image data generating and capturing means 1
1. Recognition means 12, 13; correction means 14;

The image data generation and capture means generates color image data as input image data, or captures color image data from the external device 4 as input image data. The recognition means 12 takes in the installation environment light information from the sensor 2 and recognizes it. The recognition means 13 captures and recognizes the observation environment light information from the input means 3. The correction unit 14 corrects a color conversion correspondence coefficient prepared in advance based on the installation environment light information recognized by the recognition unit 12 and the observation environment light information recognized by the recognition unit 13. The conversion means 15 converts the input image data from the image data generation / take-in means 11 into display image data using the color conversion corresponding coefficients corrected by the correction means 14 and sends out the display image data to the color display 1.

The image data is generated by the image data generation / take-in means 11,
Alternatively, the input image data captured from the external device 4 is
L ^* a ^* b ^* (hereinafter referred to as “Lab” for convenience) expressed in a uniform color space,
The image data for display obtained by the color display 1
Are expressed in an RGB color space unique to the.

FIG. 1 shows a state in which the installation environment of the color display 1 is illuminated by the illuminating light 6 from the illuminating means 5, but, of course, even if the installation environment of the color display 1 is a dark room. Good.

As shown in FIG. 2, the color image processing method of the present invention, which is performed by the color image processing apparatus 10, includes an installation environment light information recognition step 20 and an observation environment light information recognition step 3.
0, an ambient light information correction step 40, and an image data conversion step 70.

The installation environment light information recognition step 20 recognizes the installation environment light information, and the observation environment light information recognition step 30 recognizes the observation environment light information. In the ambient light information correction step 40, a color conversion coefficient is set based on the installation environment light information recognized in the installation environment light information recognition step 20 and the observation environment light information recognized in the observation environment light information recognition step 30. In the image data conversion step 70, the input image data is converted into display image data based on the color conversion coefficient determined in the ambient light information correction step 40.

As an example, as shown in FIG. 3, the environmental light information correction step 40 includes a chromatic adaptation correction step 50 and a contrast correction step 60, and the image data conversion step 70 includes
Color adaptation conversion step 80, contrast conversion step 90, illuminance correspondence conversion step 100, installation environment light correspondence display conversion step 1
10 and a display conversion step 120.

The color adaptation correction step 50 is based on the installation environment light information recognized in the installation environment light information recognition step 20 and the observation environment light information recognized in the observation environment light information recognition step 30, and a color appearance is determined. The contrast correction step 60 determines a color conversion coefficient on the uniform color space for correcting the contrast based on the installation environment light information recognized in the installation environment light information recognition step 20 on the uniform color space. Is determined.

The chromatic adaptation conversion step 80 is a chromatic adaptation correction step 5
The input image data is converted on the Lab color space by the color conversion coefficient determined at 0, and a contrast conversion step 90 is performed.
Converts the image data from the chromatic adaptation conversion step 80 into La based on the color conversion coefficients determined in the contrast correction step 60.
Convert on b color space.

The illuminance-corresponding conversion step 100 uses a previously prepared color conversion coefficient for correcting the saturation to convert the image data from the contrast conversion step 90 into a Hunt (described later) in a Lab color space. This is to correct effects and the like.

Further, an installation environment light compatible display conversion step 1
Reference numeral 10 denotes a subsequent display conversion step 120, which converts the L ^* a ^* b ^* image data from the installation environment light compatible display conversion step 110 into RGB image data unique to the display when the installation environment of the display is a dark room. In response to this, when the actual installation environment of the display is brightly illuminated, L ^* a ^* b from the illuminance conversion process 100 is used.
^{* The} image data is corrected so as to remove the influence of the reflected light from the display screen (display screen).

The conversion step for display 120 is performed as described above, and the L ^* a ^* b ^* from the conversion step 110 for display corresponding to the installation environment light is used ^.
The image data is converted into RGB image data unique to the display when the installation environment of the display is a dark room.

Here, as for the color adaptation, when entering a room illuminated with an incandescent lamp from the outside, the whole room initially feels yellowish, but after a while, it feels the same as when viewed in daylight. receive. For example, white paper looks white,
The unnaturalness of the color disappears. This is called a chromatic adaptation effect because the sensitivity of the human eye is adjusted conveniently as the user becomes accustomed to the illuminating light, and has the effect of constantly maintaining the color appearance.

Normally, when the observer observes the display in a dark room environment, the observer's eyes adapt to the display's own light emission (white in the image portion or non-image portion), but as shown in FIG. When the surroundings of the display 1 are brightly illuminated by the ambient light 6, the observer's eyes
Is also affected. In this state, it is known that the observer's eye partially adapts to both the display self-luminous light 1a and the surrounding ambient light 6, and actually adapts to a white point approximately halfway between them.

There is also a report that the display self-emission 1a and the surrounding illumination light 6 are partially adapted at a ratio of 60:40 (see N. Katoh, "P.
Radical Method for Appea
lance Match between Soft
Copy and Hard Copy "SPIEPu
replication, Vol. 2170, 170-18
1, 1994).

As shown in FIG. 4A, when the hard copy image is simulated on the display 1 in an environment where the hard copy image is observed, the color temperature of the display self-luminous light 1a is set. Hardware or software must be changed to adjust the color temperature of white to the environment to be simulated, and to correct the "color appearance" in that environment. But in this case,
The observer's eyes are also partially adapted to the ambient light 6 around the display 1 and must be corrected accordingly.

In an environment where a display is installed, a hard copy image and a display image are sometimes compared at the same time in order to match the color of a display image with the color of a hard copy image in an environment where the display is observed. Considering an extreme example, as shown in FIG. 4B, in a special situation where the display 1 is installed in a dark environment and the hard copy 8 is illuminated by a certain illumination light 9, Eyes on hard copy 8 and display 1, almost 5
It adapts partially at a ratio of 0:50.

On the other hand, as shown in FIG.
In a situation in which the display 1 is also illuminated with some illumination light 6, the observer's eyes will see the environment light 6 on the display 1 side.
As a result, the rate of adaptation to ambient light and display will be higher for ambient light.

On the display, it is necessary to make a correction in advance in consideration of such a partial chromatic adaptation state. The chromatic adaptation correction process 50 first performs such correction.

When the color of the hard copy image is simulated on the display, the white point information of both the ambient light under the hard copy observation environment and the ambient light under the display installation environment is used. Outputs an appropriate value according to the adaptation rate.

When the color of the hard copy image and the color of the display image are simultaneously compared under the display installation environment, basically, the white point of the display is adjusted to the white point of the installation environment light. To However, if the color temperature of the ambient light is, for example, 43
If the temperature is as low as about 00K, the color of the hard copy image and the color of the display image do not look the same due to the influence of incomplete adaptation described later.

When observing the display, human vision tries to adapt to the white color on the display, but when the color temperature of the ambient light around the display is low, the color adaptation is incomplete and there are individual differences. The white color looks yellowish. FIG. 5 shows the degree of this incomplete adaptation.
This is shown by the change of the color matching point when the color temperature of the display is matched with the color temperature of the installation environment light. Imperfect adaptation is thought to occur due to imperfect chromatic adaptation of the human visual system.

In consideration of such an incomplete color adaptation state,
It is necessary to apply correction in advance, and the color adaptation correction process 5
Second, 0 performs such a correction.

The specific method of the chromatic adaptation correction in the chromatic adaptation correction step 50 and the chromatic adaptation conversion in the chromatic adaptation conversion step 80 will be described in each embodiment described later.

As for the contrast correction, when the display is observed in a bright room, if the illuminance of ambient light is large, the original blackness of the display is lost, and as a result, the contrast of the entire display is lost.

The contrast correction step 60 addresses such a phenomenon. Contrast correction step 60
Correction and contrast conversion step 9
A specific method of contrast conversion at 0 will be described in Example 1 described later.

Further, regarding the illuminance-corresponding conversion, when a chromatic color is changed in illuminance and illuminated by humans, the perceived saturation (colorfulness) changes according to the illuminance. The saturation tends to look high. This is called a Hunt effect, and the illuminance-corresponding conversion step 100 corrects a change in color appearance due to the difference in illuminance.

More specifically, L ^* a from the contrast conversion step 90 is determined by a color conversion coefficient prepared in advance.
^When the brightness component L ^* of the ^* b ^* image data is large, the saturation C ^* represented by C ^* = [(a ^* ) ² + (b ^* ) ² ] ^1/2 (1) is reduced.

In addition to the Hunt effect, when a gray scale is illuminated with chromatic light, the hue of the illuminating light is felt in a light gray, and the illuminating light is felt in a dark gray in addition to the Hunt effect. Feels complementary hue to
When the n-Judd effect and the achromatic color are illuminated with different illuminances, there is a Stevens effect in which light grays appear whiter and dark grays appear blacker at high illuminance.

In the above example, the Hunt effect is corrected, but the Helson-Judd effect and the Steven effect are used.
The s effect may be corrected, or a plurality or all of them may be corrected.

A specific method of the display conversion step 110 and the display conversion step 120 corresponding to the installation environment light will be described in Example 1 described later.

FIG. 6 shows an example of a routine of the color image processing method shown in FIG. 3, which is executed by the color image processing apparatus 10 shown in FIG. The color image processing routine is
The process is started by detecting a push event of the start button by the user. First, in step S1, a dialog is opened, and then in step S2
To confirm and recognize the user's input of the illumination condition of the environment where the hard copy is expected to be observed, that is, the observation environment light information. In this case, the user can select several parameters to be specified. In this case, it is assumed that the parameters are specified by the xy chromaticity coordinates of CIE1931.

Next, the process proceeds to step S3, where the detection output of the sensor 2 shown in FIG.
The installation environment light information, which is the lighting condition of the environment where is installed, is taken in and recognized.

Next, the process proceeds to step S80, in which chromatic adaptation correction and chromatic adaptation conversion processing as described in each of the embodiments described later are performed. The processing of the correction and the contrast conversion is performed, and the process further proceeds to step S100 to perform the processing of the illuminance correspondence conversion described above.

Then, the process proceeds to step S110 to perform a display conversion process corresponding to the installation environment light as described in the first embodiment described later, and further proceeds to step S120 to perform a display conversion process. Proceeding to S130, according to the display image data obtained in step S120,
An image is displayed on the color display 1.

FIG. 7 is an example of another processing routine. When the user designates a time and instructs the processing in advance and inputs the observation environment light information, the processing is automatically performed at the designated time. This is a case where processing is started.

That is, in this case, when the designated time comes, the processing is started. First, in step S1, a dialog is opened, and then, the process proceeds to step S4, where the image processing for the ambient light is performed for the user. Check if you want to do it. On the other hand, the user gives an instruction for execution when performing image processing corresponding to ambient light, and gives an instruction for cancellation when not performing image processing.

Next, the process proceeds to step S5, where it is determined whether or not the process is to be executed based on the user's instruction. If the process is not to be executed due to the cancel instruction, the process is terminated.

When the process is to be executed in accordance with the execution instruction, the process advances to step S3 after recognizing the input observation environment light information, and fetches the detection output of the sensor 2, that is, the installation environment light information. Recognize. Subsequent steps are the same as in the example of FIG.

Hereinafter, four embodiments will be described. However,
The first to fourth embodiments are the same except for the chromatic adaptation correction step 50 and the chromatic adaptation conversion step 80, and the other steps are the same. Further, the embodiment is not limited to these embodiments 1 to 4.

In the first embodiment, in the chromatic adaptation correction step 50, a correction coefficient is obtained by a chromatic adaptation correction LUT and a least square method.
The chromatic adaptation conversion step 80 is a case where image data is converted by 3 × 8 matrix conversion.

In the second embodiment, in the chromatic adaptation correcting step 50, a correction coefficient is obtained using a chromatic adaptation model,
0 is a case where image data is converted by a three-dimensional LUT and interpolation.

In the third embodiment, in the chromatic adaptation correction step 50, a correction coefficient is obtained by the chromatic adaptation correction LUT. In the chromatic adaptation conversion step 80, as in the second embodiment, the image data is converted by a three-dimensional LUT and interpolation. It is.

In the fourth embodiment, in the chromatic adaptation correction step 50, a correction coefficient is obtained by a chromatic adaptation model and a least squares method. In the chromatic adaptation conversion step 80, image data is converted by 3 × 8 matrix conversion as in the first embodiment. This is the case for conversion.

[Embodiment 1] In the embodiment 1, as shown in FIG. 8, the chromatic adaptation correcting step 50 includes a chromatic adaptation correcting main step 51 and a chromatic adaptation conversion coefficient calculating step 55.

In this step 51, the chromatic adaptation correction L
Use UT. LUTs are prepared in a predetermined number of colors. Here, eight colors in the color reproduction range on the display in a dark room environment are selected as eight points P1 to P8 in the Lab color space as shown in FIG. The color adaptation correction main process 51 includes:
The parameters xy obtained from the installation environment light information recognition step 20 and the observation environment light information recognition step 30 are converted into color temperatures and input to this LUT.

From the first color to the eighth color as shown in FIG.
If the color temperature of the installation environment light and the color temperature of the observation environment light are input to the LUT for white as shown in FIG. Chromaticity is selected. When an intermediate value between the values prepared in the LUT is required, an interpolation value is calculated.

In the selection and calculation of the chromaticity, in the simulation of the color appearance, correction is performed in consideration of the partial adaptation state, and in the simultaneous contrast, incomplete adaptation is greatly affected. Each of these corrections must be emphasized.

Similarly, for other colors, an appropriate chromaticity of each color is selected or calculated. Such a color adaptation correction LUT is created based on statistical data obtained by color matching experiments.

Next, in the chromatic adaptation conversion coefficient calculation step 55, the mapping relationship f between the device independent values for the eight colors and the values obtained from the chromatic adaptation correction LUT is calculated.
Ask for. Here, a 3 × 8 matrix coefficient is calculated so that the color difference between each point is minimized.

In the chromatic adaptation conversion step 80, the input image data is converted by a 3 × 8 matrix operation using the coefficients calculated in the chromatic adaptation conversion coefficient calculation step 55 of the chromatic adaptation correction step 50.

FIG. 11 shows a processing routine of the chromatic adaptation correction and the chromatic adaptation conversion of the first embodiment. First, in step S81, the number n of the eight colors is set to 1, and then,
Proceeding to step S82, an appropriate chromaticity of the n-th color is selected or calculated from the chromatic adaptation correction LUT.
3, the process proceeds to step S84, where it is determined whether n is greater than 8. If it is determined that n is less than 8, the process proceeds to step S84.
Returning to 82, steps S82 and S83 are repeated.

If it is determined in step S84 that n is greater than 8, the flow advances to step S85 to calculate a 3 × 8 matrix coefficient from the chromaticity data of the eight colors obtained so far. Proceeding to step S86, the input image data is converted by a 3 × 8 matrix operation using the coefficients calculated in step S85.

In the contrast correction step 60, the parameter Y (CIE) obtained from the installation environment light information recognition step 20 is used.
An LUT that outputs a gamma value from the XYZ chromaticity coordinates Y) of 1931 is used, and data from the LUT is used as contrast correction data.

In the contrast conversion step 90, based on the contrast correction data obtained from the contrast correction step 60, the gamma of the gradation curve with respect to the lightness component L ^* of the L ^* a ^* b ^* image data from the chromatic adaptation conversion step 80. Change the value.

FIG. 12 shows a processing routine of the above-described contrast correction and contrast conversion of the first embodiment. First, in step S91, a gamma value is selected from the LUT according to the parameter Y from the installation environment light information recognition step 20, Next, the process proceeds to step S92 to convert the gamma value, and then proceeds to step S93 to store the converted gamma value in a three-dimensional LUT.
Go to 4 and use the gamma value from the three-dimensional LUT,
The image data from the chromatic adaptation conversion step 80 is converted.

As described above, in the display conversion step 120, L ^* a from the installation environment light compatible display conversion step 110 is used.
^* B ^{* In} response to converting the image data into RGB image data unique to the display when the display installation environment is a dark room, the installation environment light compatible display conversion step 110.
In the case where the actual installation environment of the display is brightly illuminated, L ^* a ^* from the illuminance correspondence conversion process 100 is used ^.
b ^{* The} image data is corrected so as to eliminate the influence of the reflected light from the display screen (display screen). For this purpose, as shown in FIG. L ^* a ^* b ^* image data is converted into XYZ chromaticity data once, and the XYZ chromaticity data is used to calculate the reflected light components Xamient, Yambie.
nt, Zambient are subtracted, and the values X _CRT , Y _CRT ,
_{Find the} Z _CRT .

Reflected light components Xamient, Yambie
nt and Zambient are values of the installation environment light when the installation environment of the display is brightly illuminated, and are given from the installation environment light information recognition step 20.

The data X _CRT , Y _CRT and Z _CRT are
Converted to L ^* a ^* b ^* image data, and further converted to L ^* a ^* b ^*
The image data is a value L ^* _CRT , a on the display screen.
^After converting to ^* _CRT , b ^* _CRT , in display conversion step 120, the image data is converted to RGB image data unique to the display.

[Second Embodiment] In the second embodiment, in a chromatic adaptation correction step 50, a correction coefficient is obtained using a chromatic adaptation model, and in a chromatic adaptation conversion step 80, image data is converted by a three-dimensional LUT and interpolation.

For this purpose, 729 (9 × 9 ×
9) Select color data. It is desirable to select so as to cover the color gamut of the display comprehensively. Then, conversion is performed on each of such color data using a color adaptation model, and an appropriate correction value is calculated. In this case, the color data is given as XYZ chromaticity coordinates of CIE1931.
If it is another coordinate system, it is once converted into XYZ chromaticity coordinates of CIE1931.

FIG. 14 shows a processing routine for chromatic adaptation correction and chromatic adaptation conversion according to the second embodiment.
In step 1, the number n of the 729 color data is set to 1, and the process proceeds to step S802 to select the n-th data from the 729 color data, and then proceeds to step S803. The selected color data is converted into the CIE 1931 XYZ chromaticity coordinates as described above,
Proceeding to step S804, the XYZ chromaticity data is converted into a cone response value LMS. Next, step S805
And normalize the cone response value LMS with the display white point cone response value.

On the other hand, an appropriate chromaticity of a white point to be corrected is obtained in advance from the installation environment light information and the observation environment light information. Specifically, as shown in FIG. 15 (the flowchart is shown in block form for convenience),
Similarly to the conversion of the nine pieces of color data, first, in step S281, the installation environment light information and the observation environment light information are converted into the XYZ chromaticity coordinates of CIE1931, respectively, and then the process proceeds to step S282. After converting the XYZ chromaticity data into the cone response value LMS, in step S283, the incomplete adaptation correction is performed on the cone response value LMS, and then the process proceeds to step S284, where the incomplete correction is performed. A partial adaptation correction is performed on the cone response value L'M'S 'after the adaptation correction.

In the processing routine of FIG. 14, step S8
05, the process proceeds to step S806.
Cone response value LwMw calculated in step S284
Using Sw, chromatic adaptation correction is performed on the cone response value normalized in step S805, and further, in step S8.
07, the cone response value after the color adaptation correction is set to CI
It is converted to XYZ chromaticity coordinates of E1931.

Thereafter, the flow advances to step S808 to convert the XYZ chromaticity data into device-independent image data L using the white point D50 data.
Convert to ^* 'a ^* ' b ^* '.

Next, the flow advances to step S809 to set n to 1
Then, the process advances to step S810 to determine whether or not n is greater than 729.
If it is determined that it is below, the process returns to step S802, and steps S802 to S809 are repeated.

If it is determined in step S810 that n is larger than 729, the flow advances to step S811 to store the 729 color data obtained so far in a three-dimensional LUT as shown in FIG. Next, step S8
Proceeding to 12, the input image data is converted based on the color data from the three-dimensional LUT.

The address of the three-dimensional LUT indicates a position in the Lab color space. When the input image data takes a value between the grid points, it is regarded as an internal dividing point of the grid point and the surrounding eight points are set. Is given as the weighted sum of the output values of the grid points of

Here, Hun is used as a color adaptation model.
t model (Reference: RW HUNT MEASUR
ING COLOUR Second Edition
ELLIS HORWOOD)
Other color adaptation models (for example, Nayatani model (Reference: Noboru Ota Color Engineering, Tokyo Denki University Press))
Etc.).

[Embodiment 3] In the embodiment 3, in the chromatic adaptation correction step 50, a correction coefficient is obtained by a chromatic adaptation correction LUT.
In the color adaptation conversion step 80, a three-dimensional LUT
And the image data is converted by interpolation. However, the LUT for eight colors is used as the chromatic adaptation correction LUT in the first embodiment, whereas the LUT for 125 (5 × 5 × 5) colors is used in the third embodiment.

FIG. 17 shows a processing routine for chromatic adaptation correction and chromatic adaptation conversion according to the third embodiment, and includes steps S81 to S8.
4 is the first embodiment shown in FIG. 11 except that the LUT for 125 colors is used as the chromatic adaptation correction LUT as described above.
And the subsequent steps S811 and S811
812 is the same as FIG. 1 except that the number of color data is 125.
This is the same as that of the second embodiment shown in FIG.

[Fourth Embodiment] In the fourth embodiment, in the chromatic adaptation correction step 50, a correction coefficient is obtained by a chromatic adaptation model and a least squares method.
The image data is converted by 8-matrix conversion.

However, the chromatic adaptation model used in the chromatic adaptation correction main step 51 of the chromatic adaptation correction step 50 is 72 in the second embodiment.
While the chromaticity for nine colors is calculated, the chromaticity for eight colors is calculated in the fourth embodiment.

FIG. 18 shows a processing routine of chromatic adaptation correction and chromatic adaptation conversion according to the fourth embodiment.
810 is the same as that of the second embodiment shown in FIG. 14 except that the chromatic adaptation model calculates the chromaticity for eight colors as described above. The subsequent steps S85 and S86 are the same as those in FIG. This is the same as that of the first embodiment shown.

[Second Embodiment] In the first embodiment described above, as shown in FIG.
Comprises a chromatic adaptation correction step 50 and a contrast correction step 60, and the image data conversion step 70 comprises a chromatic adaptation conversion step 80, a contrast conversion step 90, and an illuminance correspondence conversion step 1.
00, the display conversion step 110 and the display conversion step 120 corresponding to the installation environment light.

On the other hand, as shown in FIG. 19, the environmental light information correcting step 40 includes a chromatic adaptation correcting step 50, a contrast correcting step 60, an illuminance corresponding correcting step 43, an environmental light corresponding display correcting step 44, and a display. A correction step 45 and a color conversion coefficient synthesizing step 46 are performed, and all necessary corrections are performed on, for example, 729 pieces of color data selected in advance to calculate color conversion coefficients.

That is, in the chromatic adaptation correction step 50, the color conversion coefficient in the Lab color space for correcting the color appearance is used, and in the contrast correction step 60, the L for correcting the contrast is used.
The color conversion coefficients on the ab color space are calculated. The illuminance correspondence correction step 43 is prepared in advance,
It is assumed that a color conversion coefficient for correcting the saturation is provided.

In the installation environment light corresponding display correction step 44,
A color conversion coefficient for correcting the influence of the installation environment light upon conversion to the display-specific color space is determined. It is assumed that the display correction step 45 has a color conversion coefficient prepared in advance for conversion to a display-specific color space.

Then, in the color conversion coefficient synthesizing step 46, a chromatic adaptation correcting step 50, a contrast correcting step 60,
The color conversion coefficients obtained from the illuminance correspondence correction step 43, the installation environment light correspondence display correction step 44, and the display correction step 45 are combined, and in the image data conversion step 70, The color conversion coefficients calculated in the information correction step 40 are stored in grid points of a three-dimensional LUT, and the input image data is converted from a uniform color space to a display-specific color space.

According to the second embodiment, compared to the first embodiment shown in FIG. 3 including the above-described first to fourth embodiments, not only the chromatic adaptation correction and the contrast correction but also the color appearance All the corrections required before displaying on the display, including the correction regarding the device characteristics and the correction regarding the device characteristics, are performed in the ambient light information correction step 40, so that the load on the conversion step can be reduced.

[0100]

As described above, according to the present invention, even when the environment in which the display is installed is under general unrestricted lighting conditions, the environment in which a hard copy is expected to be observed can be obtained. Under any lighting conditions, the color of the hard copy image should be such that the color of the display image matches the color of the hard copy image actually observed in the environment expected to be observed. Appearance can be simulated on the display. Further, even when the display image and the hard copy image are compared at the same time under the installation environment of the display, the appearance impression of both can be matched.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of a color image processing system for realizing a color image processing method of the present invention.

FIG. 2 is a process chart showing a color image processing method of the present invention.

FIG. 3 is a process chart showing a first embodiment of the color image processing method of the present invention.

FIG. 4 is a diagram provided for explanation of ambient light.

FIG. 5 is a diagram provided for explaining incomplete adaptation.

FIG. 6 is a diagram illustrating an example of an image processing routine according to the first embodiment.

FIG. 7 is a diagram illustrating another example of the image processing routine according to the first embodiment;

FIG. 8 is a diagram illustrating a chromatic adaptation correction process according to the first embodiment.

FIG. 9 is a diagram provided for describing a chromatic adaptation correction process according to the first embodiment.

FIG. 10 is a diagram provided for describing a chromatic adaptation correction process according to the first exemplary embodiment.

FIG. 11 is a flowchart illustrating a processing routine for chromatic adaptation correction and chromatic adaptation conversion according to the first embodiment.

FIG. 12 is a flowchart illustrating a processing routine for contrast correction and contrast conversion according to the first embodiment.

FIG. 13 is a diagram illustrating a process of conversion for display and a conversion for display according to the installation environment light according to the first embodiment.

FIG. 14 is a flowchart illustrating a processing routine of chromatic adaptation correction and chromatic adaptation conversion according to the second embodiment.

FIG. 15 is a diagram provided for explanation of FIG. 14;

FIG. 16 is a diagram provided for explanation of FIG. 14;

FIG. 17 is a flowchart illustrating a processing routine of chromatic adaptation correction and chromatic adaptation conversion according to the third embodiment.

FIG. 18 is a flowchart illustrating a processing routine of chromatic adaptation correction and chromatic adaptation conversion according to the fourth embodiment.

FIG. 19 is a process chart showing a first embodiment of the color image processing method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Color display 2 Sensor 3 Input means 10 Color image processing apparatus 20 Installation environment light information recognition process 30 Observation environment light information recognition process 40 Ambient light information correction process 50 Color adaptation correction process 60 Contrast correction process 70 Image data conversion process 80 Color adaptation Conversion process 90 Contrast conversion process 100 Illumination-compatible conversion process 110 Installation environment light-compatible display conversion process 120 Display conversion process 43 Illuminance-compatible correction process 44 Installation environment light-compatible display correction process 45 Display correction process 46 Color conversion coefficient synthesis process

Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location H04N 1/46 H04N 1/46 Z

Claims (7)

[Claims] 1. A first step of recognizing an installation lighting condition that is an illumination condition in an environment where a color display is installed, and inputting before or after the recognition of the installation lighting condition in the first step. A second step of recognizing an observation illumination condition that is an illumination condition in an environment in which a color hard copy is predicted to be observed; an installation illumination condition recognized by the first step; and an observation illumination recognized by the second step. A third step of determining a color conversion coefficient based on the condition; and, based on the color conversion coefficient determined in the third step,
A fourth step of converting input image data into display image data. 2. The color image processing method according to claim 1, wherein said third step comprises: a chromatic adaptation correction step of determining a color conversion coefficient on a uniform color space for correcting color appearance; A contrast correction step of determining a color conversion coefficient in a color space. 3. The color image processing method according to claim 2, wherein said third step comprises: preparing a color conversion coefficient determined by said chromatic adaptation correction step; and a color conversion coefficient determined by said contrast correction step. The color conversion coefficient for correcting the saturation, the color conversion coefficient for correcting the influence of the installation environment light when converting to the display-specific color space, and the display-specific color space prepared in advance A color image processing method comprising: synthesizing a color conversion coefficient for conversion into a color space and a color conversion coefficient for converting a uniform color space to a display-specific color space. 4. The color image processing method according to claim 2, wherein the chromatic adaptation correction step comprises a step of preparing a color display under installation lighting conditions for various combinations of installation illumination conditions and observation illumination conditions. From the plurality of data pairs for matching the color appearance on the color hard copy under the observation illumination condition with the color appearance on the top, the installation illumination condition recognized in the first step and the setting illumination condition recognized in the second step A plurality of data pairs corresponding to the observation illumination conditions obtained by interpolation. 5. The color image processing method according to claim 2, wherein the chromatic adaptation correction step comprises: setting illumination conditions recognized in the first step and observation illumination conditions recognized in the second step. It uses a color adaptation model to calculate multiple data pairs to match the color appearance on a color display under installed lighting conditions with the color appearance on a color hardcopy under observation lighting conditions. Color image processing method. 6. The color image processing method according to claim 2, wherein the contrast correction step determines a color conversion coefficient for correcting the contrast from the installation illumination condition recognized in the first step. Color image processing method. 7. An image data generating / capturing means for generating or capturing color image data; a recognizing means for recognizing an installation illumination condition which is an illumination condition in an environment where a color display is installed; An input unit for inputting an observation illumination condition, which is an illumination condition in an environment predicted to be observed; and an arrangement prepared in advance based on the installation illumination condition recognized by the recognition unit and the observation illumination condition input by the input unit. Correcting means for correcting the corrected color conversion corresponding coefficient, and converting the color image data generated or captured by the image data generating and capturing means into display image data by the color conversion corresponding coefficient corrected by the correcting means. A color image processing apparatus, comprising: conversion means for converting.