JPH1093832A - Image processing unit and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain color matching between light source colors and between object colors in different color modes with high accuracy by setting a specific between a luminance of an object color and a luminance of a light source color by means of a conversion means. SOLUTION: A host 601 receives an RGB signal read by a full color scanner 600 from an original and applies prescribed image conversion processing to the signal and gives the result to a monitor 602. Preview is tried by comparing the light source color image displayed on the monitor 602 with an object color of the original. The host 601 uses white dot information and observed light source information on the monitor 602 in the image conversion processing to generate a perceptive reference white color and executes chromatic adaptation conversion processing is executed by using, e.g., the Van Kriese chromatic adaptation conversion formula based on the perceptive reference and observation light source information. In the luminance calculation of the perceptive reference white color, a relation denoted by a monotonously increasing upward convex curve is applied on a coordinate where the luminance of the object color is taken as the X axis and the luminance of the light source color is taken as the Y axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus and method for performing color processing according to a mode difference between a light source color and an object color.

[0002]

2. Description of the Related Art When comparing printed materials, color coordinates such as CIEXY are used in order to make the two colors the same.
What is necessary is just to make Z tristimulus values equal. That is, in the case of the simplest system in which it is not necessary to consider the color reproduction range or the like, when both colors are measured by a colorimeter, it is only necessary that both can be converted to have the same color coordinates.

However, when an image viewed on a monitor is printed, or when an image of a printed matter is read into a computer using an input device such as a scanner and compared with an image displayed on a monitor, one of the objects is displayed in an object color. The color of the printed material is different from that of the monitor, which is the color of the light source. It is known that when the color modes are different as described above, even if the color coordinates are matched as described above, the colors are not equal.

Accordingly, as a method of performing color matching even when the color mode is different, the present applicant calculates, for example, white as a human perception standard based on a ratio adapted to an observation light source and a monitor. Then, a method of converting an image based on the white color is proposed.

As shown in FIG. 3, the chromaticity value of white, which is the perceptual criterion, is a chromaticity (for example, CIEx, y chromaticity value) indicating the tint of white color of the observation light source and the monitor, and an adaptation ratio. Is calculated from On the other hand, as the luminance value, a value calculated by a color matching experiment, an appropriate value obtained by a simple preliminary experiment, or a value equal to the luminance obtained by colorimetry is used.

[0006] In the past, the present applicant has proposed that when the luminance value of a light source watching a printed matter is much brighter than the display limit luminance of a monitor, a value lower than luminance data obtained by measuring the printed matter is used. Also, a technique has been proposed in which the two colors are matched by displaying them on a monitor.

[0007]

In order for the two to look the same color even when the color modes are different, it is necessary to clarify the relationship between the two colors and the brightness sensation that the humans match. .

However, as described above, the relationship has been clarified with respect to the chromaticity value, but the luminance has not been clarified yet, such as using the value of a color matching experiment. In this way, the values calculated from the color matching experiment can be applied only in a limited environment, and if you want to observe in an environment different from the environment in which the experiment was performed, you do not need to perform the color matching experiment again to find the parameters. There was room for improvement, such as the lack of versatility.

Further, as described in the previous proposal, when the brightness of the printed matter is much higher than that of the monitor, it is known that the output of a value lower than the brightness of the printed matter to the monitor causes color matching. The relationship between the brightness and the brightness should be reduced. Moreover, if the brightness of the print is lower than the brightness of the monitor, it is not known that this relationship holds.

As described above, when it is desired to achieve the same color even when the light source color, the object color, and the color mode are different, the relationship between the luminance of the light source color and the luminance at the time of the color matching of the object color is hardly clarified.

An object of the present invention is to realize high-precision color matching between a light source color and an object color.

Further, the present invention shows the relationship between the brightness of both the object color and the light source color that are matched by humans in order to make the colors match even when the color modes are different. The purpose is to propose a possible method.

[0013]

SUMMARY OF THE INVENTION The present invention is characterized by having the following arrangement in order to achieve the above object.

[0014] The first invention of the present application is an image processing apparatus for performing image processing so that a light source color visually matches an object color.
Input means for inputting image data relating to the object color, and conversion means for converting the image data relating to the object color into image data relating to the light source color, wherein the conversion means comprises a horizontal axis representing the luminance of the object color, The conversion processing is performed by satisfying a relationship represented by a curve that is monotonically increasing and convex upward on a coordinate plane having the luminance of the color as the vertical axis.

According to a second aspect of the present invention, there is provided an image processing apparatus for performing image processing so that an object color visually matches a light source color, comprising: input means for inputting image data relating to a light source color; Conversion means for converting the image data of the color into image data of the object color, wherein the conversion means monotonically increases on a coordinate plane with the luminance of the object color on the horizontal axis and the luminance of the light source color on the vertical axis. , The conversion process is performed while satisfying the relationship indicated by the upwardly convex curve.

The third invention of the present application is an image processing method for performing image processing so that an object color and a light source color are visually equal in color.
Information on the observation light source is input, a luminance component in the perceptual reference white information is calculated based on the information on the observation light source, and a chromaticity component in the perception reference white information is calculated using a chromatic adaptation ratio based on the information on the observation light source. Then, a color adaptation conversion process is performed on the image data based on the calculated perceptual reference white information.

According to a fourth aspect of the present invention, the color of the monitor, which is the light source color, and the color of the printed matter, which is the object color, are visually matched to each other. In an image input / output device that performs image conversion using a value and a chromaticity value, the luminance of the perceived reference white is monotonic on a coordinate plane having the luminance of the observation light source on the horizontal axis and the luminance of the perceived reference white on the vertical axis. An image processing apparatus characterized by satisfying a relationship indicated by a curve that becomes convex upward with an increase.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION To calculate the relationship between the object color and the luminance at the time of perceived color matching of the light source color, the brightness of the printed matter is kept constant and the luminance of the monitor is changed. It was investigated. Furthermore, the brightness of the printed matter was also changed by changing the brightness of the observation light source, and the relationship between the brightness of the printed matter and the brightness of the monitor that matched the colors was obtained. As a result, it has been found that this relationship can be represented by a curve that is monotonically increasing and protrudes upward on a coordinate plane having the luminance of the object color as the horizontal axis and the luminance of the light source color as the vertical axis, as shown in FIG. Was.

Of course, the coordinates of the graph shown in FIG. 2 change depending on the observation light source or the like, but the shape of the graph does not change in any case.

Therefore, the object color and the light source color can be equalized by calculating the brightness of both to satisfy this relationship.

In addition, even when assembling into a system, the present method is used for calculating the luminance of a perceptual reference white which is a perceptual reference when observing a light source color required for adaptation conversion, and the perceptual reference white calculated in this way is used. By converting the image to the original,
Since the brightness of the entire image of the object color light source color can be converted so as to satisfy the relationship of FIG. 2, even for images having different color modes, both can be visually matched.

Hereinafter, an example of a system to which the present technique is applied will be described.

(Embodiment 1) An image input / output system having a previewer function for reading a printed matter with a scanner or the like and displaying it on a monitor and comparing the displayed image with the printed matter on the spot will be described as an example. Of course, the present invention is not limited to the present embodiment, but can be applied to any case where conversion between a light source color and an object color is performed. In the present embodiment, a process in the case of observing a printed material under the same light source as the light source on which the monitor is placed will be described.

FIG. 1 shows an outline of the system of the present embodiment. This system includes a scanner 600, a host 601,
It comprises a host 601 and a monitor 602.

The scanner 600 is a full-color scanner generally used in a color copying machine, and obtains, for example, RGB signals by reading a document image placed on a document table.

The host 601 executes image processing such as image conversion processing in accordance with observation light source information, which will be described later, based on a program stored in a hard disk in the host, and outputs the result to the monitor 602.

The monitor 602 displays a preview image corresponding to a document image based on image data from the host.

Hereinafter, the CP of the host 601 will be described with reference to FIG.
The flow of processing executed by U will be described.

The RGB image data (R1G1B1) obtained by the scanner 600 is converted into an RGB → XYZ conversion process 70
At 0, it is converted to X1Y1Z1 based on the scanner profile in which the scanner color characteristics are stored. This X1Y1Z1 is obtained based on D65, which is a standard light source in the scanner.

In the image conversion processing 701, in order to create an image in consideration of the difference between the observation light source and the color mode of the input / output image, the monitor for displaying and observing the print image, the observation light source information 703 of the monitor, and the image. Image conversion using the characteristics of (1) and (2) is performed.

The image conversion processing 701 will be described in detail with reference to FIG.

The image conversion process 701 shown in FIG. 5 includes a light source conversion process 72 for converting an image in accordance with a light source for observation.
0 and a color mode conversion process 710 for converting according to the mode of the image.

First, in a light source conversion process 720, the image is converted into an image corresponding to the observation light source. R1 which is scanner data
X converted from G1B1 with reference to standard light source (D65)
Using Equation 1, the 1Y1Z1 data is subjected to chromatic adaptation conversion into a color signal X2Y2Z2 adapted to a light source for actually observing an image.

Equation 1 is a Von Kries color adaptation conversion equation.

(Equation 1) Von Kries' color adaptation equation

[0036]

[Outside 1]

More specifically, the scanner profile 70
4, the white point (X _d65 Y _d65 Z) of the standard light source (D65) when the scanner profile is created.
The _d65) as tristimulus values of the test light and the formula 1 observation light source information _{(X wk Y wk Z wk)} 703 as a tristimulus value of the reference light
And data X2Y2Z2 matched to the light source to be observed.
Convert to The observation light source information 703 may be a value measured using an external sensor or the like, or a value selected or input by a user.

Next, in the color mode conversion processing 710, XYZ data (X2Y2Z
In 2), color mode conversion between the object color and the light source color is performed so that the display image that is the light source color and the original image that is the object color appear to be the same color.

As shown in FIG. 5, the color mode conversion processing 710 includes a perceptual reference white calculation processing 711 and an adaptation conversion processing 712 using the calculated data.

Humans see the color of an image on the basis of a certain white color. When viewing a printed matter, the color of the light source being observed is white, and when looking at the monitor, both the white color of the monitor light source and the white point of the monitor are displayed. It has been found that a certain proportion has adapted. White as a reference when viewing colors on a monitor is defined as a perceived reference white.

When comparing a printed image placed under a certain light source with a display image, a perceived reference white point of a monitor is first calculated, and a display image is created based on white data indicating the perceived reference white point.

In this embodiment, since it is assumed that the printed matter and the monitor are observed under the same light source, the observation light source information of the printed matter is equal to the observation light source information of the monitor. I have.

In the perceptual reference white calculation process 711, a perceptual reference white is created using the monitor white point information and the observation light source information 703 stored in the monitor profile.
Using this perceptual criterion and observation light source information, a chromatic adaptation conversion process using Expression 1 is performed.

As shown in detail in FIG. 6, the perceived reference white is calculated separately for chromaticity and luminance.

First, monitor white point information (X _wm Y _wm Z _wm ) stored in the monitor profile 705,
Observation light source information (X _wk Y
_wk Z _wk ) XYZ → xyY conversion processing 8 for the tristimulus values of 703
00 converts the chromaticity (xy) to the luminance (Y), chroma respectively chromaticity calculation process 801, the luminance is substituted into the luminance calculation process 802, a perceptual reference white chromaticity (x _w y _w) luminance (Y
_W ) is calculated.

As described in Japanese Patent Application No. 7-25863, the chromaticity value is defined as s where the ratio of the monitor adapts to white and 1-s where the ratio adapts to the observation light source. The values are X _wk and Y _wk , and the chromaticity values of the monitor white are X _wm and
_Assuming that Y _wm , the chromaticity values X _w and Y _w of the perceptual reference white signal can be obtained from Expression 2. This indicates that, as shown in FIG. 3, the perceived reference white as a reference for viewing the color is located between the white of the monitor and the white of the observation light source.

Here, since the adaptation ratio of the monitor and the observation light source to white is different for each observation light source at the time of image observation, the adaptation ratio s, 1-s varies depending on the observation light source. The reference white point also changes for each light source.

(Equation 2) Chromaticity value of perceptual reference white x _w = (1−s) · x _wk + s · x _wm y _w = (1−s) · y _wk + s · y _wm

The luminance of the perceived reference white color of the monitor can be estimated based on the experimental results shown in FIG. Also, even when the following Haupner equation (Equation 3) is used, if the horizontal axis is the luminance of the peripheral visual field and the vertical axis is the luminance of the test visual field, the experimental results shown in FIG. It could be confirmed.

As shown in FIG. 7, when there is a test field of different brightness in a peripheral field of view having a certain brightness as shown in FIG. 7, the brightness of the test field perceived by a human and the actual brightness are different. Is one of the expressions indicating the luminance contrast sensitivity. Here, this relationship is extended to the brightness perception relationship between the object color and the light source color, and is used as a relational expression when calculating the luminance of the perception reference white of the light source color.

In particular, in this embodiment, the luminance of the peripheral visual field is defined as the luminance of the observation light source, and the luminance of the test visual field is defined as the perceived reference white. It can be determined using Equation 3. Therefore, the relationship between the luminance value of the observation light source and the luminance value of the perceived reference white is monotonically increasing when the luminance value of the observation light source is the horizontal axis and the luminance value of the perceived reference white is the vertical axis, as in FIG. It can be said that the relationship satisfies the upward convex curve.

[0052] (Equation 3) perception reference white luminance value _{H = C t (φ) L} t n -H 0 (L u, φ) H 0 (L u, φ) = C t (φ) [S ₀ ( φ) + S ₁
(Phi) L _u ^n] H: Stimulation L _t brightness sensation L _t: luminance L _u of the test field of the apparent size expressed in minutes (visual angle) phi: ambient with viewing angle 180 ° around the test field Field-of-view luminance C _t (φ), S ₀ (φ), S ₁ (φ): function n: constant

The chromaticity values x _w and y _{w of} the perceived reference white obtained in the chromaticity calculation processing 801 and the chromaticity value Y _w of the perceived reference white obtained in the luminance calculation processing 802 are converted into xyY → XYZ conversion processing 8
03 is converted into XYZ by perceptual reference white information (X
_w Y _w Z _w ) is output to the adaptation conversion process.

[0054] Formula 2-Formula 3 perceptual reference white information calculated from _{(X w Y w Z w)} , is a light source converted based on the obtained observation light source information (X _wk Y _wk Z _wk) from such sensors The converted data X2Y2Z2 is converted again using Equation 1, and finally converted data X3Y3Z3 to be displayed on the monitor is obtained in consideration of the color mode.

Specifically, the observation light source information (X _wk Y
_wk Z _wk ) as the tristimulus value of the test light, and Equations 2 and 3
Of the monitor perceived reference white (X _w Y _w Z
By substituting _w ) into Equation 1 as the tristimulus value of the reference light, data in which not only the observation light source but also the color mode difference is corrected can be obtained.

After all, the luminance value of the observation light source and the luminance value of the perceived reference white satisfy the relationship as shown in FIG. 2 and all the colors in the image are represented by the reference data. When the input data (X1Y1Z1) of a certain color and the output data (X3Y3Z3) of the light source color after conversion are compared, the luminance (Y _wk ) of the observation light source and the perception are compared. Not only the reference white luminance (Y _w ), but also the luminance of the object color and the light source color (Y 2, Y 3) satisfies the relationship shown in FIG.

In order to convert the X3Y3Z3 in which the difference between the observation light source and the color mode has been corrected into a monitor output signal, in the XYZ → RGB conversion processing 702, R2 is calculated based on the monitor profile storing the monitor color characteristics.
It is converted to G2B2.

A comparison between the image output from the monitor based on the converted color signal and the original read by the scanner shows that even when the color modes such as the light source color and the object color are different, humans match. You can create an image that you can feel.

In the present embodiment, the luminance value and the chromaticity value of the perceived reference white are calculated by different processes according to the influence of the observation light source. Therefore, the perceived reference white color can be calculated with high accuracy, and the chromatic adaptation conversion processing between the light source color and the object color can be favorably performed.

Further, since the color adaptation conversion processing is performed on image data independent of the input / output device, the color matching processing (RGB → XYZ conversion processing, XYZ ← X) according to the scanner profile and the monitor profile.
RGB conversion processing) and chromatic adaptation conversion processing can be favorably matched.

(Modification) Unlike the first embodiment, even when the observation light source of the printed matter and the observation light source of the monitor are different light sources, the luminance of the perceived reference white can be calculated from Expression 3 above. The luminance still satisfies the same relationship as in FIG. In this case, the same effect as in the first embodiment can be obtained by substituting the monitor observation light source information at the time of calculating the monitor perception reference white using Expressions 2 and 3 and the observation light source information of the printed matter at the time of image conversion using Expression 1. Obtainable.

Here, the relationship between the luminance of the light source color and the luminance of the object color is based on the relationship of the logarithmic sensitivity of the Haupner. However, in addition to the expression expressed as the luminance contrast function and other expressions, the luminance of the object color is plotted on the horizontal axis. Any one can be applied as long as it satisfies the relationship shown by a monotonically increasing upwardly convex curve on a coordinate plane having the color luminance as the vertical axis.

(Other Embodiments) Even if the present invention is applied to a system composed of a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), even if one device (for example, a copying machine, a facsimile machine) is used. May be applied to such a device.

Also, a software program for realizing the functions of the above-described embodiment is installed in a computer in an apparatus or a system connected to the various devices so as to operate the various devices so as to realize the functions of the above-described embodiment. The invention implemented by supplying the code and causing the computer (CPU or MPU) of the system or apparatus to operate the various devices according to the stored program is also included in the scope of the present invention.

In this case, the program code itself of the software realizes the functions of the above-described embodiment, and the program code itself and means for supplying the program code to the computer, for example, the program code The storage medium storing the information constitutes the present invention.

As a storage medium for storing such a program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, magnetic tape, nonvolatile memory card, ROM or the like can be used.

When the computer executes the supplied program code, not only the functions of the above-described embodiments are realized, but also the OS (operating system) running on the computer or another program. Needless to say, the program code is included in the embodiment of the present invention even when the functions of the above-described embodiment are realized in cooperation with application software or the like.

Further, the supplied program code is stored in a memory provided in a function expansion board of the computer or a function expansion unit connected to the computer, and then stored in the function expansion board or the function storage unit based on the instruction of the program code. It is needless to say that the present invention includes a case where a provided CPU or the like performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

A plurality of tables for performing image conversion processing according to certain observation light source information, a scanner profile, and a monitor profile are prepared in advance, an arbitrary table is selected, and the image conversion processing is performed using the selected table. You can go.

[0070]

According to the present invention, color matching between the light source color and the object color can be realized with high accuracy.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an outline of a system according to a first embodiment.

FIG. 2 is a diagram illustrating the relationship between the luminance of an object color and the luminance of a light source color when performing color matching.

FIG. 3 is a diagram illustrating a relationship between chromaticities when calculating white as a perceptual reference.

FIG. 4 is a diagram illustrating a data flow according to the first embodiment;

FIG. 5 is a diagram showing an image conversion process in detail.

FIG. 6 is a diagram showing a perceptual reference white calculation process in detail.

FIG. 7 is a diagram showing experimental conditions for luminance contrast sensitivity.

Claims (14)

[Claims] 1. An image processing apparatus for performing image processing so that a light source color is visually equal to an object color, comprising: input means for inputting image data relating to the object color; Conversion means for converting the image data into colors, wherein the conversion means is a curve that is monotonically increasing and convex upward on a coordinate plane having the luminance of the object color as the horizontal axis and the luminance of the light source color as the vertical axis. An image processing apparatus that performs a conversion process while satisfying a relationship represented by: 2. A first correction unit that corrects the image data of the object color based on an input characteristic of an input device, and outputs the corrected image data of the object color to the conversion unit; 2. The image processing apparatus according to claim 1, further comprising a second correction unit configured to perform a correction according to an output characteristic of the output device on the image data on the light source color. 3. An image processing apparatus according to claim 1, wherein said conversion means is adapted to an observation light source. 4. An image processing apparatus for performing image processing so that an object color visually matches a light source color, comprising: input means for inputting image data related to a light source color; Conversion means for converting the image data into colors, wherein the conversion means is a curve that is monotonically increasing and convex upward on a coordinate plane having the luminance of the object color as the horizontal axis and the luminance of the light source color as the vertical axis. An image processing apparatus that performs a conversion process while satisfying a relationship represented by: 5. An image processing method for performing image processing so that an object color and a light source color are visually equal in color, comprising: inputting information relating to an observation light source; and a luminance component in perceptual reference white information based on the information relating to the observation light source. Calculating the chromaticity component in the perceptual reference white information using the chromatic adaptation ratio according to the information on the observation light source, and performing chromatic adaptation conversion processing on the image data based on the calculated perceptual reference white information An image processing method comprising: 6. A color adaptation conversion of input image data to image data dependent on the observation light source based on the information on the observation light source, and performing a color adaptation conversion process based on the calculated perceptual reference white information. The image processing method according to claim 5, wherein 7. A recording medium for storing a program for implementing the image processing method according to claim 6. 8. An image processing method for performing image processing such that a light source color visually matches an object color, wherein: an input step of inputting image data relating to the object color; A conversion step of converting the image data into color-related image data, wherein the conversion means has a curve that is monotonically increasing and convex upward on a coordinate plane having the luminance of the object color as the horizontal axis and the luminance of the light source color as the vertical axis. An image processing method comprising: performing a conversion process while satisfying a relationship represented by: 9. A recording medium for storing a program for realizing the image processing method according to claim 8. 10. An image processing method for performing image processing so that an object color visually matches a light source color, wherein: an input step of inputting image data relating to the light source color; A conversion step of converting the image data into color-related image data. An image processing method comprising: performing a conversion process while satisfying a relationship represented by: 11. A recording medium for storing a program for realizing the image processing method according to claim 10. 12. A luminance value and a chromaticity value of a perceived reference white as a reference of color perception when observing a monitor in order to visually match a color of a monitor which is a light source color and a color of a printed matter which is an object color. In the image input / output device that performs image conversion using, the luminance of the perceived reference white is monotonically increased upward on a coordinate plane with the luminance of the observation light source on the horizontal axis and the luminance of the perceived reference white on the vertical axis. An image processing apparatus characterized by satisfying a relationship represented by a curve. 13. The relationship that is monotonically increasing and convex upward is as follows:
13. The image input / output device according to claim 12, wherein the image input / output device is a quadratic curve. 14. The method according to claim 1, wherein the following equation of Hauwner is used for the conversion of the luminance.
The image input / output device according to the above. _{H = C t (φ) L} t n -H 0 (L u, φ) H 0 (L u, φ) = C t (φ) [S ₀ (φ) + S ₁
(Phi) L _u ^n] H: Stimulation L _t brightness sensation L _t: luminance L _u of the test field of the apparent size expressed in minutes (visual angle) phi: ambient with viewing angle 180 ° around the test field Field-of-view luminance C _t (φ), S ₀ (φ), S ₁ (φ): function n: constant