JP2001036758A - Color correction processing method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a color transformation corresponding to the entire range of lightness between black and white colors by subtracting the value set in a black color space shown by a 1st image output means from the value set in a color space of image data on the 1st image output means, performing the color transformation of the subtracted value by means of a color transformation parameter and adding the value set in the black color space shown by a 2nd image output means to the value obtained via the color transformation. SOLUTION: A color space transformation part 16 subtracts the 3-stimulus value of the display enable black colors of a color monitor 14 and a color printer 24 from the 3-stimulus value of white colors of the monitor 14 and the printer 24 to obtain the matrix elements of a color space transformation matrix M. A color transformation part 18 subtracts the 3-stimulus value of black color to be displayed on the monitor 14 from the 3-stimulus value (X1, Y1, Z1) to be displayed on the monitor 14, multiplying the subtracted value by a color transformation matrix M and adds the 3-stimulus value of the display enable black color of the printer 24 to the multiplication result to obtain the 3-stimulus value (X2, Y2, Z2) which are displayed on the printer 24.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color correction for displaying an image obtained by two or more image output means by matching the range of lightness that can be displayed when at least values in a black color space are different. A processing method, in which white and black in a hard copy image such as a photograph or a printed matter and a soft copy image displayed by a self-luminous display means such as a CRT display device or a liquid crystal display device can be corrected and displayed. The present invention belongs to the technical field of a color correction processing method for performing color correction corresponding to the entire range of lightness.

[0002]

2. Description of the Related Art Today, color CRT monitors, color liquid crystal monitors, color printers, and the like have become widespread and are widely used as color image output devices. These image output devices usually include R (red), G (green), B (blue), C (cyan), M (magenta), Y (yellow), C,
By controlling the image data for M, Y, and K (black), a color image having a desired color can be displayed or printed out. However, since such color image data depends on the output characteristics and spectral sensitivity characteristics of the image output device, when outputting to image output devices having different characteristics,
It is necessary to perform color conversion of image data in consideration of the characteristics. In particular, since the spectral sensitivity characteristics are greatly different between a color CRT monitor or a color liquid crystal monitor and a color printer, for example, the color of an image displayed on a color CRT monitor should match the color of an image output to a color printer to some extent. In addition, it is necessary to optimize the color conversion to match the appearance of the colors.

On the other hand, color image data consisting of R, G, B, C, M, and Y is converted into image data that does not depend on an image input / output device such as a scanner, a color CRT monitor, and a color printer. Tristimulus values (X, Y, Z) and CIE of the CIEXYZ display system specified by the Commission (CIE)
The image data is converted into image data such as lightness L ^* (brightness) and perceived chromaticity indices a ^* and b ^* (hue and saturation) of the L ^* a ^* b ^* color system, and are identical in the color space of these display color systems. If it is image data, no matter how the image corresponding to this image data is output to the image output device, the tristimulus values (X, Y, Z)
There is a method in which color matching (color matching) can be achieved at a colorimetric value level by matching colorimetric values measured by a color measuring device.

However, in the above-mentioned method, color matching can be performed by aligning colorimetric values only between hard copy images printed by a color printer or the like. Color CR
In the case of a self-luminous image output device such as a T monitor or a color liquid crystal monitor, the color temperature is about 9300K and the display screen has a bluish tint, while it is printed on white paper output by a color printer or the like. When observing an image under a light bulb as an observation light source, for example, its color temperature is
It is yellowish in degree, the difference between the two color temperatures is large,
The displayable color space also differs greatly. Therefore, it is difficult to match color appearances by aligning colorimetric values. Furthermore, in addition to the above-described large difference in color temperature between a self-luminous image output device such as a color CRT monitor and a non-self-luminous image output device such as a color printer, the influence of chromatic adaptation due to differences in image output methods and viewing environments. Even if the colorimetric values are aligned in a state where is removed, the color appearance does not always match.

[0005] In view of this, it is conceivable that color conversion is performed by utilizing the concept of a chromatic adaptation model by von Kries and Naya to match colors. For example, in a color correction method for performing color conversion using a von Kries color adaptation model, the tristimulus values (X, Y, Z) of a CIEXYZ display system of an object under test light and the corresponding values when the reference light is changed. Utilizing the fact that there is a linear relationship converted by the matrix between the tristimulus values (X ′, Y′Z ′) of the color, the tristimulus values under other illumination light of which the color temperature changes are calculated. Can be calculated. For example, by converting color image data of tristimulus values of a color CRT monitor into a color space that can be displayed by a color printer and displaying the color space on a color CRT monitor, the color CRT monitor is displayed.
The color appearance of an image displayed on an RT monitor or the like can be matched to a certain extent with the color appearance of an image output by a color printer or the like. Japanese Patent Application Laid-Open No. 9-219800 discloses a color correction processing apparatus for performing chromatic adaptation correction using the method of von Kries.

[0006]

However, these color complements
In the positive method, color conversion of the color space is performed based on all white.
If the black color is different in the color space,
Does not match the brightness of black. An example
For example, a color CRT image display device and a color printer
Color CRT image display when matching the color appearance between
The displayable brightness of the device is CIEL^*a^*b^*Color system
Lightness L^*Is generally 0 to 100, while the color pre
The lightness that can be displayed based on the white
Exponent L^*5 to 100, the lowest brightness of black
Degree L^*Are different (lightness L^*Indicates that the maximum value is white and the minimum value is black
Color). In order to match the appearance of colors,
Need to match, so a certain color correction is needed
It is said. In the above example, the lightness L ^*The maximum value of
That is, the white color matches in the color space, but the white color is different
If the appearances of the images differ, color correction is naturally required.

Therefore, when the color correction is linearly performed on the lightness L ^{* of} the CIEL ^* a ^* b ^* color system, in the above example, the minimum value of the lightness L ^* of the color printer is 5, which is offset. Therefore, there is a problem that the offset equally affects the tone difference due to the overall brightness and changes the brightness of the image. Further, after converting the image data into tristimulus values (X, Y, Z) of the CIEXYZ display system, which is a luminance space, color conversion is performed using a method by von Kries, etc. CIEL ^* a ^* b ^*
In the color system, there is a problem that the hue angle changes under the influence of lightness and saturation, and the hue is not maintained by the color conversion. In particular, after performing a certain process by performing a color conversion, an inverse conversion may be performed. In this case, however, there is a problem that the hue is not restored.

Therefore, the present invention solves the above-mentioned problem, and associates a color space in which black that can be displayed is different depending on the observation light source and the output means, to correspond the entire range of brightness from black to white. It is an object of the present invention to provide a color correction processing method and a color correction processing apparatus for performing color conversion by performing color conversion. Furthermore, even when color conversion to a different color space is performed depending on the observation light source and output means, and then the color conversion is reversed and the color space is returned to the color space before the color conversion, the hue is always maintained. It is another object to provide a processing method and a color correction processing device.

[0009]

According to a first aspect of the present invention, an image data in a color space of a first image output means is displayed by the first image output means. When performing color conversion on the color space of the second image output means having different values on the black color space, the values on the black color space displayed by the first and second image output means are subtracted. The color spaces of the first and second image output means having the black as the origin are obtained respectively, and the color spaces of the first and second image output means having the black as the origin are associated with the color spaces. A color conversion parameter is obtained in advance, and the first image output means uses the first data from the value in the color space of the image data.
The value in the black color space represented by the image output means is subtracted, converted using the color conversion parameter, and the value obtained by performing the conversion is displayed by the second image output means. By adding the values on the black color space,
An object of the present invention is to provide a color correction processing method characterized by performing color conversion.

Here, it is preferable that the color space is a luminance space. Preferably, the color conversion is conversion using chromatic adaptation correction.

After converting the image data of the first image output means into a luminance space, performing the color conversion using the above-described color correction processing method, and performing color conversion on the color space of the second image output means. By adjusting the lightness or saturation of the color-converted image data in the uniform color space, the representative point located in the same hue plane in the uniform color space as the image data of the first image output means is adjusted. It is preferable to obtain image data located on the hue plane in the uniform color space of the converted representative point obtained by performing the color conversion.

In a second aspect of the present invention, the color space of the first image output means and the color space of the second image output means having at least a different black color space in the color space are associated with each other, and A color correction processing device for performing color conversion, wherein a value in a black color space that can be displayed by the first image output means is converted into a color space of image data output to the first image output means. Subtracts from the represented image data, and this subtracted value is
The color conversion is performed by using a color conversion parameter obtained in advance from a color space obtained by subtracting a value on each black color space displayed by the first and second image output means, and performing this color conversion. By adding the value in the black color space displayed by the second image output means to the value obtained by the above, the image data of the first image output means is converted to the image data of the second image output means. Another object of the present invention is to provide a color correction processing device including a color conversion unit for converting a color into a displayed color space.

In a third aspect of the present invention, the image data in the color space of the first image output means is converted into at least one color space of black and white displayed by the first image output means. When performing color conversion on the color space of the second image output unit having a different upper value, the color space of the second image output unit is converted into the color space of the first image output unit in advance. A color space is obtained, and the brightness or saturation of the image data in the color space of the first image output means is adjusted and corrected according to the shape of the converted color space on the uniform color space, Thereafter, a color correction processing method characterized by performing color conversion on the corrected image data is provided.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a color correction processing apparatus for performing a color correction processing method according to the present invention will be described in detail based on a preferred embodiment shown in the accompanying drawings.

FIG. 1 shows an embodiment of a color correction processing apparatus for implementing the color correction processing method according to the first aspect of the present invention. A color correction processing device 10 shown in FIG. 1 is a device that processes image data sent from a scanner / image processing device 12 for color correction and outputs the processed data to a color monitor 14 or a color printer 24. color space conversion unit 16 for performing T ₁
A color conversion unit 18 for performing color conversion T ₂ , a brightness / saturation adjustment unit 20 for performing brightness / saturation adjustment T ₃ of image data, and an RGB space conversion unit 22 for obtaining output data suitable for the color monitor 14. And a CMY space conversion unit 26 that obtains image data suitable for the color printer 24. Note that the color space described in the present specification may be any space that can uniquely determine color characteristics,
Luminance space represented by CIEXYZ display system and CIEL ^*
A uniform color space represented by the a ^* b ^* color system and the CIEL ^* u ^* v ^* color system may be used.

The scanner / image processing device 12 takes in image data to be output to the color monitor 14 and performs desired image processing, for example, image processing for color balance adjustment, contrast correction, and brightness correction, and magnification caused by a lens. This device performs chromatic aberration correction processing, distortion aberration correction processing, scanner color shift correction processing, electronic scaling processing, sharpness enhancement correction, and the like. Image data is sent to the color space conversion unit 16 of the color correction processing apparatus 10. send.

The color space conversion unit 16 of the color correction processing device 10
Is red (R) obtained by the scanner / image processing device 12,
Image data of each pixel of green (G) and blue (B) is color-matched
CIEXYZ display using a transformation matrix determined by the function
Color space conversion T for converting to tristimulus values (X, Y, Z) of the system₁
I do. The image data by the R, G, and B pixels is R,
Using the tristimulus values of the three primary colors G and B, the image data is
Tristimulus value (X₁, Y₁, Z₁Can be converted to
You. In this embodiment, the tristimulus values of the CIEXYZ display system
(X, Y, Z), but not necessarily
Not limited to tristimulus values, X in CIE1964 display system_TenY
_TenZ_TenTristimulus value (X_Ten, Y_Ten, Z_Ten)
It may be replaced.

The color conversion unit 18 performs color conversion T ₂ on the data of the tristimulus values (X ₁ , Y ₁ , Z ₁ ) obtained by the color space conversion unit 16 and displays the data on the color printer 24. This is a part for obtaining three stimulus values (X ₂ , Y ₂ , Z ₂ ).
Conventionally, color conversion is based on only white, that is, a color in the displayable white color space of the color monitor 14 in which the luminance values of the R, G, and B pixels of the color monitor 14 are maximized, and white printer 24, for example, combining the color on the white color space of paper illuminated by D ₅₀ light source had to match the color appearance. Therefore, even after the color conversion is performed, the color monitor 14 and the color printer 24
In the color space, for example, the brightness of black that can be displayed by the color printer 24 is 5, and the brightness of black that can be displayed by the color monitor 14 is sometimes 0. Therefore, the color monitor 14 and the color printer 2
The lightness of the displayable white and black color spaces of No. 4 could not be completely matched.

For this reason, the color converter 18 converts the data of the tristimulus values (X ₁ , Y ₁ , Z ₁ ) obtained by the color space converter 16 into a color conversion T according to the following equation (1). ₂ is performed and converted into tristimulus values (X ₂ , Y ₂ , Z ₂ ).

(Equation 1)

Here, X _1k , Y _1k and Z _1k are tristimulus values (X
_1k , Y _1k , Z _1k ), X _2k , Y _2k and Z
_2k is a value of a tristimulus value (X _2k , Y _2k , Z _2k ) on a black color space that can be displayed by the color printer 24. That is,
In the color conversion T ₂ , the black tristimulus values (X _1k , Y _1k , Z _1k ) displayed on the color monitor 14 are converted from the tristimulus values (X ₁ , Y ₁ , Z ₁ ) displayed on the color monitor 14. The value is subtracted and the value is multiplied by a color conversion matrix M. That is, the offset amount of the black tristimulus value of the color monitor 14 is subtracted in advance and multiplied by the transformation matrix M. Then, color printer 2
Four displayable black tristimulus values (X _1K , Y _1K , Z _1K ) are added.

Note that the conversion matrix M for performing the color conversion T ₂ is represented by vo
In the method by von Kries, white tristimulus values (X _1w , X _1w ,
Y _{1 w,} Z _{1 w)} and white color printer 24, for example, D ₅₀ light source of a white tristimulus value of the paper _{(X 2w, Y 2w, Z} 2w)
, The matrix element of the conversion matrix M is obtained. The color conversion unit 16 _calculates the white tristimulus values (X _1w ,
Y _1w , Z _1w ) and the white tristimulus values (X _2w , Y _2w , Z _2w ) of the color printer 24, the black tristimulus values (X _1K , Y _1K , Z) that can be displayed on the respective color monitors 14. _1K )
And the corrected white tristimulus values ( _X1w ', _Y1w ', _Z1w ') obtained by subtracting the black tristimulus values ( _X2K , _Y2K , _Z2K ) that can be displayed by the color printer 24. And (X _2w ′, Y _2w ′, Z _2w ′).

As described above, the black 3
Conversion matrix M to a value obtained by subtracting the offset of the stimulus value in advance
, And then add the tristimulus values (X _1K , Y _1K , Z _1K ) of black that can be displayed by the color printer 24, and add the tristimulus values (X ₂ , Y ₂ ,
Z ₂ ). Obtained tristimulus values (X ₂ , Y ₂ , Z ₂ )
Is sent to the brightness / saturation adjustment unit 20.

The color conversion T ₂ performed by the color conversion unit 18 is
The method is not limited to a method using a conversion matrix used for performing chromatic adaptation correction by the method according to von Kries, but may be any method that can use a conventional color conversion method for performing color conversion based on white.

The lightness / saturation adjusting unit 20 adjusts the tristimulus values (X ₂ , Y ₂ , Z ₂ ) to adjust the tristimulus values (X ₂ , Y ₂₎ .
₂ , Z ₂ ) CIEL ^* a ^* b ^{* of} uniform color space determined from
The hue angle in the color system, that is, b ^* / a ^* is kept constant. The CIEL ^* a ^* b ^* color system is
Using tristimulus values (X, Y, Z), the following equation (2)
４ (4) can be obtained. ^{L * = 116 (Y / Y} n) (1/3) -16 (2) a * = 500 {(X / X n) (1/3) - (Y / Y n) (1/3)} ( 3) b ^* = 200 ｛(Y / Y _n ) ^(1/3) − (Z / Z _n ) ^(1/3) ｝ (4) Here, X _n , Y _n and Zn are reference _values. These are tristimulus values.

Generally, when the color conversion section 18 performs the color conversion T ₂ , the hue angle b ^* / a ^* changes, and the hue slightly changes. For example, as shown in FIG. 2, CIEL ^* a ^* b ^* color coordinates of the located A ₁ to A ₆ point on the color system is changed, by moving each of the points A ₁ '~A _6' If the hue changes and the color space shape changes from S ₁ to S ₂ , the point A ₁
Hue plane P composed of colors having the same hue angle as
Is converted to a curved surface P ′ by a color conversion T ₂ . That is, the color having the same hue by the color conversion T ₂ are, not necessarily identical hues. This is because the linearly converted tristimulus values (X, Y, Z) are determined by the non-linear equations of the above equations (3) and (4), and a ^* and b ^* change. For this reason, the same hue plane is not maintained by the color conversion T ₂ , and if the hue plane P is subjected to the color conversion T ₂ and then the inverse conversion T ₂ ⁻¹ , the hue does not return to the original hue plane P. .
Therefore, the lightness / saturation adjusting unit 20 outputs the tristimulus values (X ₂ ,
Y ₂ , Z ₂ ) to adjust the tristimulus values (X ₂ , Y ₂ ,
Z ₂₎ of uniform color space determined from CIEL ^* a ^* b ^* configured to maintain a constant hue angle or b ^* / a ^* in the color system.

That is, tristimulus values (X ₁ , Y ₁ , Z ₁ )
Image data and CIEL ^* a ^* b ^* color system on, the hue plane formed by the representative points after conversion obtained by performing color conversion T ₂ to the representative points located on the same hue plane of 3 The three stimulus values (X ₃ , Y ₃ , Z ₃ ) are adjusted using the brightness / saturation adjustment T ₃ so that the image data of the stimulus values (X ₁ , Y ₁ , Z ₁ ) are converted.
Z ₃ ). For example, as shown in FIG. 2, a point C ₁ having image data of tristimulus values (X ₁ , Y ₁ , Z ₁ )
As it converted into '' the same hue plane P having a hue angle equal to the 'representative point A ₁ after conversion by the color conversion T ₂ of the representative point A ₁ have the same hue, i.e., CIEL ^* a ^*
b ^* to the constant b ^* / a ^* on the color system, L ^*,
Adjust a ^* and b ^* . Thus, tristimulus values _{(X 1, Y 1, Z} 1) C 1 point is image data of the lightness and saturation adjustment T ₃ what is converted to a point C ₁ 'by the original color conversion T ₂ To a point C ₁ ″. Consequently, for the same hue plane P '', even if the inverse conversion of the color conversion T _2, can be returned to the same hue plane P, it is possible to maintain the hue angle.

[0027] Note that the method of adjusting the lightness and saturation adjustment T _3, within hue plane formed by the representative points after the conversion, in which lightness and saturation adjustment is performed such that the image data is converted Any one can be used, but CIEL
^* a ^* b ^* Color difference on color system (ΔL ^{* 2} + Δa ^{* 2} + Δb ^{* 2} )
^(1/2) (ΔL ^* , Δa ^*, and Δb ^* are the amounts of change in L ^* , a ^*, and b ^* due to brightness / saturation adjustment), the smaller the better. The selection of the representative point is not particularly limited, but preferably corresponds to the number of hues provided in a look-up table (LUT) including a large number of data sets.

The RGB space conversion unit 22 is a color monitor 1
This is a part for obtaining image data (R, G, B) by conversion so as to conform to the spectral sensitivity characteristic of No. 4. CMY space conversion unit 2
Reference numeral 6 denotes a portion for obtaining image data (C, M, Y) by conversion so as to match the spectral sensitivity characteristics of the color printer 24. In this way, the image data displayed on the color monitor 14 is obtained, and the entire brightness from black to white displayed on the color monitor 14 is changed from the entire brightness from black to white displayed on the color printer 24. And the same color of the image displayed on the color printer 24 is
The same hue can be maintained in the color monitor 14 as well.

The conversion from the input to the output of the image data of the color correction processor 10 may be individually processed using a conversion formula for each component, or may be collectively obtained by a look-up table. It may be configured as follows.

Next, an example of the color correction method of the present invention will be described.
Based on a color correction method implemented in the processing apparatus 10.
I will tell. First, the image obtained by the scanner / image processing device 12 was obtained.
The image data is converted to the spectral sensitivity characteristics of the scanner's reading sensor.
Image data (G_r,
G_b, G_b), And the converted image data
Is subjected to the desired image processing described above,
Sent to 10. In the color correction processing device 10, as shown in FIG.
First, the image signal read by the scanner
Represents image data (G_r,
G_g, G_b) Is the color space conversion T₁According to CIEXY
The tristimulus value of the Z display system (X₁, Y₁, Z ₁Is converted to
You. Tristimulus value (X₁, Y₁, Z₁) Is given by the following equation (5).
As shown, the tristimulus values for each of the primary colors R, G and B
(X_r, Y_r, Z_r), (X_g, Y_g, Z_g)and
(X_b, Y_b, Z_b) To image data (G_r, G_g,
G_b) Element G _r, G_gAnd G_bEach corresponding three stimuli
The value is multiplied as a coefficient and expressed as a linear sum.

(Equation 2)

Next, the obtained tristimulus values (X ₁ , Y ₁ , Z
₁ ) is subjected to color conversion T ₂ to obtain tristimulus values (X ₂ , Y ₂ , Z
₂ ) get. The color conversion T ₂ is performed according to the above equation (1). That is, in the color conversion T ₂ , the tristimulus values (X ₁ , Y ₁ , Z ₁ ) displayed on the color monitor 14 are converted to the black tristimulus values (X _1k , Y _1k , Z) displayed on the color monitor 14.
_1k ) is subtracted, and the value is multiplied by a color conversion matrix M.
That is, before multiplying the color conversion matrix M, the color monitor 1
The offset of the black tristimulus value of 4 is subtracted in advance. After multiplying by the color conversion matrix M, the tristimulus values (X _1B , Y _1B , Z _1B ) of black that can be displayed by the color printer 24 are added, and the tristimulus values (X ₂ , Y ₂ , Z ₂ ).

In the color conversion T ₂ , black tristimulus values are subtracted in advance, color conversion is performed based on a conversion matrix M based on white, and then black tristimulus values that can be displayed by the color printer 24 are added. Therefore, it is possible to correct the difference in color appearance due to the difference in white while making the offset adjustment based on the difference in lightness of black one-to-one corresponding to the brightness. The lightness of black is represented by the lightness value of the CIEL ^* a ^* b ^* color system, that is, L ^*
Is not directly converted to a linear value, so that the offset adjustment of the black L ^* value does not evenly affect the gradation on the display image on the color monitor 14. Since this correction is performed in a luminance space such as a CIEXYZ display system,
The value in the black luminance space is smaller than the value in white, and the influence on the gradation on the display image is small from medium brightness to high brightness by offset adjustment.

Next, the color conversion T_TwoTristimulus values (X
₁, Y₁, Z₁Hue angle b)^*/ A ^*Are the same
EL^*a^*b^*The representative point on the color system, i.e.,
Color conversion T_TwoThe converted representative converted by
The color conversion T so that the phase angles of the points are the same_TwoTo give
Tristimulus value (X_Two, Y_Two, Z_TwoKey)
And adjust the tristimulus value (X_Three, Y_Three, Z_ThreeGet) And
For example, as shown in FIG. 2, tristimulus values (X₁,
Y₁, Z₁) Is CIEL^*a^*b^*Point C on color system
₁And the same color located on the same hue plane P as this point
Representative point A with phase₁Is the color conversion T_TwoConverted by
A₁’, The point C₁Is the transformation T_ThreeBy
Is the representative point A after conversion₁Point on the same hue plane P '' as
C₁''.

When the same hue plane is converted by the color conversion T ₂ , for example, as shown in FIG. 2, the same hue plane P is originally converted to a curved surface P ′, and the hue is no longer constant. Hue changes. In this case, the brightness, ie L ^*
When values and saturation i.e. ^{(a * 2 + b * 2} ) (1/2) the value freely adjust the performs inverse transformation T ₂ ^-1 of the color conversion T _2, the hue does not return to the original. Therefore, the color hue after performing a color transformation T _2, by color before conversion is corrected hue after conversion obtained by performing color conversion T ₂ in the same representative color, then the inverse transformation T _{Even if 2} ^-1 is applied, the original hue can be restored.

From the tristimulus values (X ₃ , Y ₃ , Z ₃ ) obtained by the lightness / chroma adjustment T ₃ , RGB image data (R, G, B) conforming to the signal of the color monitor 14 is obtained.
R, G, and B can be obtained by multiplying the tristimulus values (X ₃ , Y ₃ , Z ₃ ) by a conversion matrix determined according to the color printer 24. The image data (R, G, B) thus obtained is sent to the color monitor 14. On the other hand, image data (C, M, Y) to be output to the color printer 24 can be obtained by multiplying the tristimulus values (X ₁ , Y ₁ , Z ₁ ) by a conversion matrix determined according to the color monitor printer 24. In this way, the brightness and saturation are adjusted, and white and black can be output to the color monitor 14 and the color printer 24 in one-to-one correspondence.

The color correction in the present embodiment, the difference in the displayable color space of the color monitor 14 and a color printer 24 due to the difference in the color space of white and black, the color conversion T ₂
Is associated with, further, the performed lightness and saturation adjustment T _3, a color having the same hue is converted to the same color.

FIG. 4 shows a color correction processing device 50 for implementing the color correction processing method according to the third embodiment of the present invention. The color correction processing device 50 shown in FIG. 4 performs processing for color correction on image data output from the scanner / image processing device 12 and output to the color monitor 14, and performs color correction processing on the color printer 24 and the color monitor 14. A color space conversion unit 16 that performs a color space conversion T ₁ , a lightness / saturation adjustment unit 54 that performs a lightness / saturation adjustment T ₄ of image data, and a lightness / saturation adjustment T ₄ . Color conversion T for the image data obtained by
₂ color conversion unit 18 that performs a CMY space converter 26 to obtain an output data suitable for the color printer 24, a color monitor from the image data subjected to brightness and saturation adjustment T ₄ 14
And an RGB space conversion unit 22 for obtaining image data conforming to. In the color correction processing device 50, when the components are the same as the components of the color correction processing device 10, the same identification numbers are given and the description of the configuration is omitted. In the third aspect of the color correction processing method of the present invention, color conversion is not limited to the color conversion T ₂ based on the equation (1), if the conventional color conversion such as a known method by the color adaptation correction Good.

The brightness / saturation adjustment unit 54 performs the inverse conversion T ₂ ^-1 of the color conversion T ₂ by the equation (1) or the like in advance from the known color space of the color printer 24 to the color space of the color monitor 14. The converted color space is obtained, and the image data of the tristimulus values (X ₅ , Y ₅ , Z ₅ ) obtained by the color space conversion unit 16 is adjusted to match the shape of the converted color space on the uniform color space. And CI
The lightness L ^* and saturation (a ^{* 2)} on the EL ^* a ^* b ^* color system
+ B ^{* 2} ) Adjust ^(1/2) . Thus, by performing the color correction processing unit 10 the color conversion T _2, then different as to adjust the brightness or saturation in the color space of the color printer 24, before performing the color conversion T _2, pre-color Since the image data is adjusted in such a manner that the color space of the printer 24 corresponds to the conversion color space obtained by performing the inverse conversion T ₂ ^-1 , the color space is converted to the color space of the color printer 24 by performing the color conversion T _2. afterwards,
Even if the color conversion is performed to the color space of the color monitor 14 by performing the inverse conversion T ₂ ^-1 , the hue can be preserved. The components other than the brightness / saturation adjustment unit 54 are the same as the components of the color correction processing device 10.

Next, an example of the third color correction method of the present invention will be described based on a color correction method implemented in the color correction processing device 50. First, the scanner / image processing device 12 obtains image data of three primary colors of R, G and B from image data depending on the scanner determined by the spectral sensitivity characteristics of the reading sensor of the scanner. The obtained image data is subjected to desired image processing, and the image data output to the color printer 24 is sent to the color correction processing device 50. In the color correction processing device 50, first, as shown in FIG.
_r , G _g , G _b ) are CIE according to the color space conversion T ₁ .
It is converted into tristimulus values (X ₅ , Y ₅ , Z ₅ ) of the XYZ display system. The tristimulus values (X ₅ , Y ₅ , Z ₅ ) are, as shown in equation (5), the tristimulus values (X _r ,
_Yr , _Zr ), ( _Xg , _Yg , _Zg ) and ( _Xb , Y
_b , Z _b ) to the element G of the image data (G _r , G _g , G _b )
_r , G _g, and G _b are multiplied as coefficients of the corresponding tristimulus values and expressed as a linear sum.

Next, the obtained tristimulus values (X ₅ , Y ₅ , Z
₅ ) On the other hand, the brightness / saturation adjustment T ₄
^* a ^* b ^* Lightness L ^* and chroma on the color system (a ^{* 2} + b
^{* 2} ) The adjustment of ^(1/2) is performed, and the tristimulus values (X ₆ , Y ₆ ,
Z ₆ ). Conventionally, color conversion T _{2 is} performed, and then lightness L
^* To have been adjusted by and saturation ^{(a * 2 + b * 2} ) (1/2), then performs an inverse transform T ₂ ^-1, when returning to the color space of the color printer 24, CIEL ^* a ^* The hue angle b ^* / a ^* on the b ^* color system is the original image data ( _Gr , G
_g , _Gb ), the hue angle b ^* / a ^* obtained on the color printer 14 does not match. However, before performing the color conversion T ₂ to be described later, since adjusting the image data, the hue is retained even applies transform T ₂ ^-1 · T _2. As for the method of adjusting the brightness and the saturation, the image data is adjusted by comparing the color space of the color printer 24 in advance with the shape of the color space subjected to the inverse transformation T ₂ ^-1 . For example, an image is formed on a curve in a color space determined from a curved surface obtained by performing an inverse transform T ₂ ^-1 on a hue surface in the color space of the color printer 14 and a hue surface in the color space of the color monitor 14 of interest. Adjust the brightness and saturation so that the data points come.

Thereafter, color conversion T ₂ is performed to obtain tristimulus values (X ₇ , Y ₇ , Z ₇ ) on the color space of the color printer 24. From the obtained tristimulus values (X ₇ , Y ₇ , Z ₇ ), image data (C, M, Y) is obtained as image data output to the color printer 24, and sent to the color printer 24. In addition, 3 obtained by performing the lightness / saturation adjustment T ₄
From the stimulus values (X ₆ , Y ₆ , Z ₆ ), image data (R, G,
B) is obtained and sent to the color monitor 14.

As shown in FIG. 6, the spatial shape in the six color space displayed on the color monitor 14 is S ₁ , and the space shape in the six color space corresponding to the color monitor 14 displayed on the color printer 24 is S ₁ . The space shape is S ₂ , and the color space shape S ₂ is
When the color space shape S ₃ is converted into the color space shape S ₃ by performing the inverse conversion T ₂ ⁻¹ , it is desirable that the color space shape S ₃ originally matches the color space shape S ₁ , but does not always match. Therefore, image data of a color space shape S in _{1 (G r, G g,} G b) a point on the uniform color space obtained from, while comparing a color space shape S _3, corrects the brightness and saturation. In this way, for example, a corrected hue Q is obtained. Thereafter, performs color conversion T _2.

[0043] Thus, the image data of the color monitor 14, before performing the color conversion T _2, since the adjustment of the brightness or chroma, then performs color conversion T _2, further inverse transformation T ₂ ^-1
And the hue does not change from the original hue.

The color correction processing method and the color correction processing apparatus according to the present invention have been described in detail above. These color correction processing apparatuses perform conversion and adjustment of a portion configured for color correction by using respective functions. Or a lookup table (LUT) having a large number of data sets for collectively performing all conversions and adjustments configured for color correction. Good. The present invention is not limited to the above embodiments, and various improvements and modifications may be made without departing from the spirit of the present invention.

[0045]

As described above in detail, according to the present invention, a color space in which black that can be displayed is different depending on the observation light source and the output means is associated, and the brightness from black to white is adjusted. Color conversion can be performed corresponding to the entire range. Further, even when color conversion to a different color space is performed depending on the observation light source and output means, and then the color conversion is reversed to return to the color space before the color conversion, the hue can always be maintained. .

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a color correction processing apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating an example of a color correction processing method according to the present invention.

FIG. 3 is a flowchart illustrating an example of a color correction processing method according to the present invention.

FIG. 4 is a block diagram illustrating a color correction processing apparatus according to another embodiment of the present invention.

FIG. 5 is a flowchart illustrating another example of the color correction processing method of the present invention.

FIG. 6 is an explanatory diagram illustrating another example of the color correction processing method of the present invention.

[Explanation of symbols]

 10, 50 color correction processing unit 12 scanner / image processing unit 14 color monitor 16 color space conversion unit 18 color conversion unit 20, 54 brightness / saturation adjustment unit 22 RGB space conversion unit 24 color printer 26 CMY space conversion unit 52 inverse conversion Department

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5B057 AA11 CA01 CA08 CA12 CB01 CB08 CB12 CC01 CE16 DB02 DB06 DB09 5C077 LL19 MP08 PP31 PP32 PP33 PP37 PQ12 SS06 TT02 5C079 HB01 HB02 HB05 HB11 LA03 LB02 MA05 PA03

Claims (6)

[Claims] An image data in a color space of a first image output means is converted into a color space of a second image output means having a different value in a black color space displayed by the first image output means. When the color conversion is performed, the color space of the first and second image output units having the black as the origin is obtained by subtracting a value in the black color space displayed by the first and second image output units. Ask for each,
Using this, the first and the second with the black as the origin
A color conversion parameter corresponding to the color space of the image output means, and the color space of the black represented by the first image output means from a value on the color space of the image data of the first image output means. Subtracting the above value, performing conversion using the color conversion parameter, and adding a value in the black color space displayed by the second image output means to a value obtained by performing the conversion. A color correction processing method characterized by performing color conversion by using 2. A color correction processing method according to claim 1, wherein said color space is a luminance space. 3. The color correction processing method according to claim 1, wherein the color conversion is conversion using chromatic adaptation correction. 4. The image data of the first image output means is converted into a luminance space, the color conversion is performed using the color correction processing method according to claim 2, and the color space of the second image output means is converted. After the color conversion, the lightness or saturation of the color-converted image data in the uniform color space is adjusted, and the image data of the first image output unit is positioned in the same hue plane in the uniform color space. A color correction processing method comprising: obtaining image data located in a hue plane on a uniform color space of a converted representative point obtained by performing the color conversion on the representative point to be converted. 5. A color correction processing device for performing color conversion on image data by associating a color space of a first image output means with a color space of a second image output means having at least a different black color space in the color space. Subtracting a value in a black color space that can be displayed by the first image output means from image data expressed in a color space of image data output to the first image output means; The color conversion is performed by using a color conversion parameter obtained in advance from the color space obtained by subtracting the value in the black color space displayed by the first and second image output means from the subtracted value. By adding a value on the black color space displayed by the second image output means to the value obtained by performing the color conversion, the image data of the first image output means 2 on the color space displayed by the image output means Color correction processing device characterized by comprising a color conversion unit for conversion. 6. The image data in the color space of the first image output means is converted into a second color image having a different value in at least one of the black and white color spaces displayed by the first image output means.
When the color conversion is performed on the color space of the image output unit, the color space of the second image output unit is converted into the color space of the first image output unit to obtain a conversion color space. According to the shape of the color space in the uniform color space, the brightness or saturation of the image data in the color space of the first image output means is adjusted and corrected, and then the corrected image is corrected. A color correction processing method comprising performing color conversion on data.