JPH11232449A - Color image processing method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To naturally reproduce even a color image that has high chroma saturation. SOLUTION: A 1st lightness calculation part 32 finds the 1st lightness value L*i1 , based on an input color and the lightness ranges of input and output systems. A 2nd lightness calculation part 33 calculates the 2nd lightness value L*i2 based on the input color, the lightness ranges of input and output systems, the lightness of the color that has the same hue as the input color and has the highest chroma saturation in the input system and the lightness of the color that has the same hue as the input color and has the highest chroma saturation in the output system. A saturation ratio calculation part 34 calculates a saturation ratio (h). based on the RGB value, etc., of the input color. Then a lightness control part 35 sets the lightness L*i , between the 1st and 2nd lightness value in response to the saturation ratio (h).

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. In particular, the present invention relates to a color image processing method and apparatus in a case where a color reproduction range of an output system differs from a color reproduction range of an input system.

[0002]

2. Description of the Related Art Hereinafter, a CRT (additive color mixture using three RGB input colors) is used as an input system, and a color printer such as an electrophotographic system or an inkjet system is used as an output system.
The following description will be made with reference to an example of three color inks of n, Magenta, and Yellow, or subtractive color mixing using four color inks obtained by adding Black to the three colors.

In general, the color reproduction range differs between a CRT and a color printer, and the color reproduction range of the color printer is generally smaller than the color reproduction range of the CRT, although there is a partial reversal.

As a processing method for reproducing a high-quality color image when the color reproduction ranges of the input system and the output system are different, first, the difference in the brightness range in the input / output system is adjusted, and then the difference in the saturation is adjusted. The method of adjusting is common. A specific example of this method will be described with reference to the drawings.

FIG. 10 is a diagram in which the horizontal axis represents saturation and the vertical axis represents lightness in the hue of the input color to be processed. In the figure, the outer triangle indicates the color reproduction range igm of the input system in that hue, and the inner triangle indicates the color reproduction range ogm of the output system in the hue. Further, the position (black circle position) to which the symbol “i” is attached indicates an input color to be processed, the position (black circle position) indicating “ims” indicates the maximum chroma color of the input system in the hue, and “oms”. (Black circle position) indicates the maximum chroma color of the output system in that hue.

First, the brightness is adjusted so that the brightness of the input color falls within the range of the brightness of the output system. This adjustment is generally made proportionally using information on the brightness range of the input system and the brightness range of the output system. FIG. 11 shows a state in which the adjustment of the brightness has been completed. I ′ in FIG. 11 is a color obtained by performing brightness adjustment on the input color.

After the brightness adjustment is completed, saturation adjustment is performed.
For saturation adjustment, a method of proportionally adjusting the saturation range of each input / output system is considered, but here,
It is assumed that all colors outside the saturation range of the output system are adjusted by a clipping method that replaces the colors at the edges of the output system color reproduction range. The position (black circle position) with the symbol “i ″” in FIG. 11 is a color (output color) obtained by performing saturation adjustment on the color i ′. In this way, the input colors can be kept within the color reproduction range of the output system.

[0008]

The above-mentioned conventional method has the following problems.

When the color reproduction range is adjusted by the above-described method, the output system after the adjustment maintains the lightness balance but decreases the saturation. This problem becomes more pronounced as the saturation of the input color increases. When reproducing natural images such as photographs on the output system, this phenomenon is not a major problem, but when reproducing artificial color graphics using many primary colors on the output system, the decrease in saturation adversely affects the quality. Will be exerted.

The present invention provides natural color reproduction without reducing the saturation even when reproducing artificial color graphics and the like using a large number of primary colors in an output system, and even when reproducing natural images such as photographs. An object of the present invention is to provide a method for adjusting a color gamut of an input / output system which can be maintained.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above-mentioned object, and a first aspect of the present invention is to adjust the brightness of an arbitrary input color according to an output system and then output the adjusted color. In the color image processing apparatus, an adjustment range setting unit for setting a range for adjusting lightness (hereinafter, referred to as a “lightness adjustment range”), a saturation evaluation unit for obtaining an index value reflecting the saturation of an input color, and the index A color image processing apparatus comprising: a brightness adjustment unit that sets a brightness value of an output color within the brightness adjustment range according to a value.

The adjustment range setting means corresponds to the brightness range of the input system, the brightness range of the output system, the brightness of the input color, the brightness of the maximum saturation color in the input system having the same hue as the input color, and the input color. It is preferable to have upper limit value setting means for setting an upper limit value of the lightness adjustment range based on the lightness of the maximum chroma color in the output system at the same hue as the output color.

[0013] The adjustment range setting means is configured to determine a brightness range of an input system, a brightness range of an output system, and a brightness of an input color.
It is preferable to have a lower limit value setting means for setting a lower limit value of the brightness adjustment range.

It is preferable that the adjustment range setting means changes the brightness adjustment range according to the hue of the input color.

The adjustment range setting means includes a hue of an input color,
Lightness range of input system, lightness range of output system, lightness of input color,
Set the upper limit of the lightness adjustment range based on the lightness of the maximum chroma color in the input system at the same hue as the input color, and the lightness of the maximum chroma color in the output system at the same hue as the output color corresponding to the input color. It is preferable to have an upper limit value setting unit that performs the operation.

The upper limit value setting means includes a storage means for storing a table defining an adjustment coefficient set for each hue, an input color hue adjustment coefficient, an input system lightness range, an output system lightness range, The brightness adjustment range based on the brightness of the input color, the brightness of the maximum chroma color in the input system at the same hue as the input color, and the brightness of the maximum chroma color in the output system at the same hue as the output color corresponding to the input color. And an arithmetic means for calculating the upper limit value of.

[0017] The adjustment range setting means may be configured to determine a brightness range of an input system, a brightness range of an output system, and a brightness of an input color.
It is preferable to have a lower limit value setting means for setting a lower limit value of the brightness adjustment range.

According to a second aspect of the present invention, in a color image processing method in which the brightness of an arbitrary input color is adjusted according to an output system and then output, a range in which the brightness is adjusted (hereinafter referred to as a "brightness adjustment range"). ) Is set, an index value reflecting the saturation of the input color is obtained, and the brightness value of the output color is set within the brightness adjustment range according to the index value. Provided.

The difference between the lightness of the color with the highest saturation in the same hue as the input color and the highest lightness or the lowest in the same hue as the input color, and the lightness of the input color and the highest in the same hue as the input color. Or the ratio of the difference between the lowest lightness and the lightness of the color with the highest saturation in the same hue as the output color corresponding to the input color and the highest or lowest lightness in the same hue as the output color. The brightness value of the output color corresponding to the input color and the ratio of the difference between the highest brightness or the lowest brightness in the same hue as the output color with respect to the difference are obtained, and the brightness adjustment is performed. It is preferable to set the upper limit of the range.

The ratio of the difference between the minimum lightness and the maximum lightness in the input system and the difference between the minimum lightness and the lightness of the input color is the lightness stored for the difference between the minimum lightness and the maximum lightness in the output system. It is preferable to determine a value and use this as the lower limit of the brightness adjustment range.

According to a third aspect of the present invention, in a color image processing method for adjusting the brightness of an arbitrary input color according to an output system and outputting the adjusted color, a range in which the brightness is adjusted (hereinafter referred to as a "brightness adjustment range"). Is set according to the hue of the input color, an index value reflecting the saturation of the input color is obtained, and the brightness value of the output color is set within the brightness adjustment range according to the index value. Is provided.

The difference between the lightness of the color with the highest saturation in the same hue as the input color and the highest lightness or the lowest lightness in the same hue as the input color is the lightness of the input color and the highest in the same hue as the input color. Or the ratio of the difference between the lowest lightness and the lightness of the color with the highest saturation in the same hue as the output color corresponding to the input color and the highest or lowest lightness in the same hue as the output color. A lightness value in which both the ratio of the lightness of the output color corresponding to the input color to the difference and the ratio of the difference between the highest lightness or the lowest lightness in the same hue as the output color is obtained, is calculated. It is preferable that a value obtained by integrating the coefficient values set according to the hue be the upper limit value of the lightness adjustment range.

The ratio of the difference between the minimum lightness and the maximum lightness in the input system and the difference between the minimum lightness and the lightness of the input color is the lightness stored with respect to the difference between the minimum lightness and the maximum lightness in the output system. It is preferable to determine a value and use this as the lower limit of the brightness adjustment range.

[0024]

Embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 The color image processing apparatus according to Embodiment 1 adjusts the lightness according to the saturation of an input color so that a highly saturated image can be reproduced more naturally. Is the biggest feature.

First, the outline of the main features of this apparatus will be described with reference to FIG. Details of each part will be described later for each part.

The color space used in the present invention may be any color space that can be separated into lightness and hue information. In the present embodiment, CIE L *
The description will be made using the a * b * color space.

This color image processing apparatus includes an input color space information storage section 30, an output color space information storage section 31, a first brightness calculation section 32, a second brightness calculation section 33, a saturation calculation section 34, and a brightness adjustment section 35. , Saturation adjustment section 36 and output color reproduction section 3
7 is provided. Input color space information storage unit 30
Has white CIE XYZ values (X
_iw , Y _iw , Z _iw ), white lightness value (L * _iw ), black lightness value (L * _ik ), and a 3 × 3 matrix (MTX [3] [3] for converting RGB values into XYZ values ]) Are stored. The output color space information storage unit 31 stores white lightness value (L * _ow ), black lightness value (L * _ok ), and cyan (L * _c , a * _c , b * _c ) in the output color space. , Magenta (L * _m , a * _m , b * _m ), yellow (L * _y , a * _y , b * _y ), red (L * _r , a * _r , b * _r ), blue (L * _b , a * _b , b * _b ) and green (L * _g , a * _g , b * _g ) CIE at 100% printing
L * a * b * values are stored.

Data input from outside (R of input color i)
The GB value (R _i , G _i , B _i ) is calculated by the first lightness calculation unit 32,
It is input to the second lightness calculator 33 and the saturation calculator 34. First brightness calculating unit 32, RGB values of the input color _{i (R i, G i,} B i) on the basis of, CIE L * a * b * value _{(L * i1, a * i} , b * i) the calculate. This L * _i1 (hereinafter referred to as “first brightness value (L * _i1 )”) is exclusively
This is determined from the viewpoint that the lightness of the input color i falls within the lightness range of the output system, and does not consider the saturation. That is, the first lightness value (L * _i1 )
The brightness ratio is stored independently of the hue. In particular,
The first lightness value (L * _i1 ) is obtained by _calculating the ratio of the difference between the lowest lightness and the highest lightness in the input system and the difference between the lowest lightness and the lightness of the input color by the minimum lightness and the highest lightness in the output system. Is a brightness value calculated to be stored for the difference (see FIG. 4). Various data necessary for the calculation are stored in the input color space information storage unit 30 and the output color space information storage unit 3.
I get it from 1. The first lightness calculator 32 outputs the CIE L * a * b * values (L * _i1 , a * _i , b * _i ) thus obtained to the lightness controller 35.

The second lightness calculator 33 calculates the RGB values of the input color i.
Based on the values (R _i , G _i , B _i ), a second lightness value (L
* Calculate _i2 ). The second lightness value (L * _i2 ) is a value in the output system lightness range determined in consideration of the lightness of the maximum saturation point of the output system depending on the hue. Specifically, the second
Lightness value (L * _i2) is the lightness L * _ims and up to the input color i of the same hue lightness L * _iw most having high saturation color ims input color i of the same hue (or minimum lightness L * _ik ), the ratio of the difference between the lightness L * _i of the input color i and the highest lightness L * _iw (or the lowest lightness L * _ik ) of the same hue as the input color i, and the input Difference between the lightness L * _{oms of the} color oms having the highest saturation in the same hue as the output color corresponding to the color i and the highest lightness L * _ow (or the lowest lightness L * _ok ) in the same hue as the output color. And the ratio of the difference between the lightness of the output color corresponding to the input color i and the highest lightness L * _ow (or the lowest lightness L * _ok ) of the same hue as that of the output color. Of the output color (see FIG. 5). Various data necessary for the calculation are obtained from the input color space information storage unit 30 and the output color space information storage unit 31. The second brightness calculating unit 33 outputs the obtained second brightness value (L * _i2 ) to the brightness adjusting unit 35.

The saturation calculating section 34 calculates a saturation h indicating the degree of vividness of the input color i based on the RGB values (R _i , G _i , B _i ) of the input color i. Various data necessary for the calculation are obtained from the input color space information storage unit 30 and the output color space information storage unit 31. The saturation calculator 34 outputs the calculated saturation h to the brightness controller 35.

The brightness adjuster 35 calculates the saturation h calculated by the saturation calculator 34 and the CIE calculated by the first brightness calculator 32.
CIE L * a * b * based on the L * a * b * values (L * _i1 , a * _i , b * _i ) and the second brightness value (L * _i2 ) calculated by the second brightness calculation unit 33. The values (L * _i , a * _i , b * _i ) are obtained and output to the saturation adjusting unit 36. That is, the brightness adjusting unit 35
Adjusts the brightness according to the saturation h so that the brightness of the input color i falls within the brightness range of the output system. The brightness value (L * _i ) is set between the first brightness value (L * _i1 ) and the second brightness value (L * _i2 ) according to the magnitude of the saturation h. As the saturation h of the input color i decreases (ie, approaches an achromatic color), the first lightness value (L
* Adjust the brightness to approach _i1 ). Conversely, input color i
Increases the saturation h (that is, becomes a vivid color)
, The lightness is adjusted so as to approach the second lightness value (L * _i2 ). When the saturation h = 0, L * _i = L *
_{When i1} and the saturation h = 1, L * _i = L * _i2 .

The saturation adjusting section 36 adjusts the CIE L * to make the saturation of the input color i fall within the saturation range of the output system.
The saturation of the a * b * value (L * _i , a * _i , b * _i ) is adjusted by a known method, and the result is set as the CIE L * a * b * value (L * _i ,
a * _i , b * _i ).

The output color reproduction section 37 outputs the CIEL * a * b * value (L) of the input color i within the color reproduction range of the output system.
* _i , a * _i , b * _i ) are converted into output color signals that can be output by a known method.

As described above, the color image processing apparatus according to the present embodiment can reproduce a highly saturated image more naturally by adjusting the brightness according to the saturation h.

The outline of the main features has been described above.

The "brightness adjustment range" referred to in the claims is a section defined by the first brightness value and the second brightness value in the first embodiment.
The “adjustment range determining means” refers to the input color space information storage unit 3
0, a first lightness calculator 32, a second lightness calculator 33, and an output color space information storage 31. The “index value” corresponds to the saturation h. The “saturation evaluation unit” is realized by the saturation calculator 34 and the output color space information storage 31. “Brightness adjusting means” corresponds to the brightness adjusting unit 35. The “upper limit setting unit” is realized by the input color space information storage unit 30, the output color space information storage unit 31, and the second brightness calculation unit 33. The “lower limit setting unit” is realized by the input color space information storage unit 30, the output color space information storage unit 31, and the first lightness calculation unit 32. However, since the above-described units operate in close cooperation with each other, the correspondence described here is not strict.

Hereinafter, the above components will be described in detail with reference to FIGS.

First, the details of the first lightness calculator 32 in FIG. 1 will be described.

The first lightness calculator 32 calculates the first lightness value (L * _i1 ). As described above, the first lightness value (L * _i1 ) is a value that preserves the lightness ratio independently of the hue and is within the output system lightness range. The details will be described below.

The first lightness calculating section 32 stores an RGB → XYZ conversion matrix (MTX) in the input color space information storage section 30.
[3] [3]), the RGB values (R _i ,
G _i , B _i ) are converted to CIE XYZ values by a known method. Further, referring to the white CIE XYZ values (X _iw , Y _iw , Z _iw ) of the input color space information storage unit 30, the CIE L * a * b * values (L * _i , a * _i , b
* _i ).

Subsequently, the first lightness calculating section 32 outputs the white lightness (L * _iw ) and the black lightness (L * _ik ) from the input color space information storage section 30, and the output color space information storage section. 3
The brightness of white (L * _ow ) and the brightness of black (L
* _ok ) get. Then, a first lightness value (L * _i1 ) is calculated using these (see FIG. 4). First lightness value (L *
_i1 ) is a distance (brightness difference) [L * _ow−
L * _ok] and the distance ratio of (lightness _{difference) [L * i 1 -L *} ok] is the distance (lightness _{difference) [L * iw -L * ik} ] a distance (lightness difference)
It is the same as the ratio of [L * _i -L * _ik ] and within the output system brightness range. Specifically, L * _i1 is calculated by solving the following equation.

L * _i1 = ((L * _i −L * _ik )) ÷ (L * _iw −
L * _ik )) × (L * _ow− L * _ok ) + L * _ok Finally, the first lightness calculator 32 calculates the CIE L * a * b * values (L * _i1 , a *) _i , b * _i ) are output to the brightness controller 35.

Next, the details of the second brightness calculation section 33 in FIG. 1 will be described with reference to FIGS. 2, 5, 6, and 8.

The second brightness calculating section 33 calculates the second brightness value (L * _i2 ). As already mentioned, this second lightness value (L * _i2 ) depends on the hue,
This value is within the output system lightness range in consideration of the lightness of the maximum saturation point of the output system. The details will be described below.

The second brightness calculation section 33 includes a maximum saturation RGB value calculation section 40, an RGB → LAB conversion section I41, and an RGB → L
It comprises an AB conversion section II42, an output system maximum saturation point calculation section 43, and a second brightness calculation core section 44.

Data input from outside (R of input color i)
The GB values (R _i , G _i , B _i ) are input to the maximum saturation RGB value calculation unit 40, the RGB → LAB conversion unit II42, and the output system maximum saturation point calculation unit 43.

The maximum saturation RGB value calculation section 40 calculates the input color i
Based on the RGB values (R _i , G _i , B _i ) of the input color i, a color ims having the same hue as the input color i and having the highest saturation in the input system.
The GB value (R _ims , G _ims , B _ims ) is calculated. The specific calculation method is as follows (see FIG. 8).

First, the maximum chroma RGB value calculating section 40 orders RGB based on the magnitude of the RGB values (R _i , G _i , B _i ) of the input color i. To generalize and explain,
Here, the one having the largest value is expressed as UP _i , the one having the next largest value is expressed as MIDLE _i , and the one having the smallest value is expressed as LOW _i . At this time, the RGB values (R _ims , G _ims , B _ims ) of the color ims having the same hue and the highest saturation are as follows.

UP _ims 1.0 MIDLE _ims (1.0 ÷ (UP _i −LOW _i )) ×
(MIDLE _i -LOW _i ) LOW _ims 0.0 where the RGB values (R _i , G _i , B _i ) are normalized to 0.0 to 1.0 as shown in FIG. .

For example, UP → R, MIDLE → G, LO
If W → B, the RGB values (R _ims , G _ims , B _ims ) of the color ims having the same hue and the highest saturation are as follows.

R _ims = 1.0 G _ims = (1.0 ÷ (R _i −B _i )) × (G _i −B _i ) B _ims = 0.0 The maximum saturation RGB value calculation unit 40 The RGB values (R _ims , G _ims , B _ims ) of the color ims having the same hue as the input color i and having the highest saturation in the input system are obtained as described above.
Output to the LAB conversion unit I41.

The RGB → LAB conversion unit I41 outputs the RGB value (R) of the color ims having the same hue as the input color i and the highest saturation in the input system, which is input from the maximum saturation RGB value calculation unit 40.
_ims , G _ims , B _ims ) by the first lightness calculator 32 (FIG. 1).
By the same operation as the above, the CIEL * a * b * value (L * _ims , a *
_ims , b * _ims ). And it outputs this of L * _{im s} to the second brightness calculating core unit 44.

The RGB → LAB conversion section II 42 outputs the input color i
CIE L * a * based on the RGB values (R _i , G _i , B _i ) of the first lightness calculation unit 32 (FIG. 1).
The b * value (L * _i , a * _i , b * _i ) is calculated. Then, the obtained (L * _i , a * _i , b * _i ) is output to the second brightness calculation core unit 44 and the output system maximum saturation point calculation unit 43.

The output system maximum chroma point calculation unit 43 stores the cyan (L) in the output color space from the output color space information storage unit 31.
* _c , a * _c , b * _c ), magenta (L * _m , a * _m , b * _m ), yellow (L * _y , a * _y , b * _y ), red (L * _r , a *) _r , b * _r ), blue (L * _b , a * _b , b * _b ), and green (L * _g , a * _g , b * _g ) at the time of 100% printing of CIE L * a * b * Get the value. Also, as described above, the RGB → LAB conversion unit
From II42, the CIE L * a * b * values (L * _i ,
a * _i , b * _i ).

Then, the output system maximum chroma point calculation unit 43
It is determined which of the hue sections formed by red, yellow, green, cyan, blue, and magenta on the hue plane is included in the input color i. In the description here, as shown in FIG.
It shall be in the red-yellow section.

Next, the output system maximum saturation point calculation section 43 calculates the intersection of a straight line connecting the input color and the origin and a straight line connecting red and yellow (this intersection corresponds to the position of the color oms) on the hue plane. _H ) component value (a * _oms , b * _oms ). The intersection can be calculated by solving the following simultaneous equations.

B * _oms = (b * _i ÷ a * _i ) × a * _oms b * _oms = ((b * _r− b * _y ) ÷ (a * _r− a * _y )) × a * _oms
+ (A * _r * b * _y- a * _y * b * _r ) ÷ (a * _r- a * _y ) Subsequently, the output-system maximum chroma point calculation unit 43 calculates the red-yellow distance on the hue plane. , The ratio of the intersection-red distance calculated above is calculated. If this ratio is S, S can be calculated by the following equation.

S = (distance between oms and red) ÷ (distance between yellow and red) Next, the calculated ratio S, red lightness (L * _r ), and yellow lightness (L * _y ) are used. Calculates the intersection om
The brightness of s (L * _oms ) is calculated.

As described above, the output system maximum saturation point calculation unit 43 determines that the input color i has the same hue and the output system as L * _oms = S × L * _y + (1.0−S) × L * _r. The most saturated color oms C
The IE L * a * b * values (L * _oms , a * _oms , b * _oms ) can be calculated. The output system maximum chroma point calculation unit 43 outputs the calculated L * _oms to the second brightness calculation core unit 44.

The second lightness calculation core unit 44 firstly receives the lightness of the input system white (L * _iw ) and the lightness of the input system black (L * _ik ).
From the input color space information storage unit 30. Also, RGB
→ The lightness (L * _ims ) of the color ims having the same hue as the input color i and the highest saturation in the input system is obtained from the LAB conversion section I41.
Further, the color component values (a * _i , b * _i ) of the input color i are obtained from the RGB → LAB conversion unit II42. When the lightness (L * _i ) of the input color i is larger than the lightness (L * _ims ) of ims, the ims-white distance (lightness difference) in the lightness axis direction.
And the ratio between ims and the distance (brightness difference) of the input color i is calculated and defined as S1 (see FIG. 5A). Conversely, when the lightness (L * _i ) of the input color i is smaller than the lightness (L * _ims ) of ims, the distance between ims-black (lightness difference) and the distance between ims-input color i (lightness) in the lightness axis direction. The difference is calculated as S1.

Subsequently, the second lightness calculation core unit 44 outputs the lightness of the output system white (L * _ow ) and the lightness of the output system black (L * _ow ).
* _ok ) is obtained from the output color space information storage unit 31. Also,
The output system maximum saturation point calculation unit 43 outputs the lightness (L) of the color oms having the same hue as the input color i and having the highest saturation in the output system.
* _oms ) get. Then, a second brightness value (L * _i2 ) within the output system brightness range is calculated by performing a proportional calculation using the previously calculated distance ratio S1 (see FIG. 5B). Specifically, L * _i2 is calculated by solving the following equation. L * _i> L * when the _{ims L * i2 = S1 × L} * oms + (1.0-S1) × L * ow L * i ≦ L * For _{ims L * i2 = S1 × L} * oms + ( 1.0−S1) × L * _ok The second lightness calculator 33 calculates L * _i2 obtained as described above.
Is output to the brightness adjusting unit 35.

Next, details of the saturation calculator 34 of FIG. 1 will be described with reference to FIGS.

The saturation calculating section 34 is for calculating the saturation h indicating the vividness of the input color i. As shown in FIG. 3, the saturation calculator 34 includes a maximum saturation RGB value calculator 50, an RGB → LAB converter I51, and an RGB → LA
A B conversion unit II 52 and a saturation calculation core unit 53 are provided.

Data input from outside (R of input color i)
The GB values (R _i , G _i , B _i ) are input to the maximum saturation RGB value calculation unit 50 and the RGB → LAB conversion unit II 52.

The RGB → LAB converter II 52 outputs the input color i
CIE L * a * based on the RGB values (R _i , G _i , B _i ) of the first lightness calculation unit 32 (FIG. 1).
The b * value (L * _i , a * _i , b * _i ) is calculated. Then, the calculated (L * _i , a * _i , b * _i ) is output to the saturation calculating core unit 53.

The maximum saturation RGB value calculation unit 50 calculates the input color i
Based on the RGB values (R _i , G _i , B _i ) of
By the same operation as the B value calculation unit 40 (FIG. 2), RGB values (R _ims , G _ims , B _ims ) indicating the color ims having the same hue as the input color i and having the highest saturation in the input system are calculated. This is output to the RGB → LAB conversion unit I51. Continue, RGB
→ The LAB conversion unit I51 includes a maximum saturation RGB value calculation unit 50.
The RGB values (R _ims , G _ims , and G _{ims) of} the color ims having the same hue as the input color i and having the highest saturation in the input system,
B _ims ) is _converted to a CIE L * a * b * value (L * _ims , a * _ims , b) by the same operation as the first lightness calculation unit 32 (FIG. 1).
* _ims ) and outputs this to the saturation calculation core unit 53.

The saturation calculation core unit 53 firstly outputs RGB →
Input from LAB conversion section I51, the input color i of the same hue at and most having high saturation color hue component values ims input system and _{(a * i ms, b *} ims), from RGB → LAB converter unit II52 Based on the input hue component values (a * _i , b * _i ) of the input color i, the saturation of each color is calculated by a known method. Here, the saturation of ims is Sims, and the saturation of i is Si.

Next, the saturation calculation core unit 53 converts the RGB →
The brightness (L * _ims ) of _ims is obtained from the LAB conversion unit I51. Further, the brightness (L * _i ) of the input color i is obtained from the RGB → LAB converter II 52. Further, the input color space information storage unit 3
From 0, the lightness of the input system white (L * _iw ) and the lightness of the input system black (L * _ik ) are obtained. Then, the brightness of the input color i (L *
_{If i} ) is greater than the lightness of ims (L * _ims ), the distance of ims-white in the lightness axis direction (lightness difference) is:
The ratio between ims and the distance (brightness difference) of the input color i is calculated, and this is defined as S1 (see FIG. 7). Conversely, if the lightness (L * _i ) of the input color i is smaller than the lightness (L * _ims ) of ims, the ims-black distance (lightness difference) in the lightness axis direction and the ims-input color i The ratio with respect to the distance (brightness difference) is calculated and set as S1.

After that, the saturation calculation core unit 53 performs a proportional calculation using the saturation Sims calculated previously,
The saturation Sims ′ corresponding to the lightness of i is calculated. Specifically, Sims' is calculated by solving the following equation.

Sims' = S1 × Sims Finally, the saturation calculating core unit 53 calculates the saturation h by solving the following equation.

H = Si ÷ Sims' The saturation calculating section 34 calculates the saturation h obtained as described above.
Is output to the brightness adjusting unit 35 (see FIG. 1).

Next, details of the brightness adjusting section 35 of FIG. 1 will be described.

The lightness adjusting section 35 outputs a first lightness value (L
* _i1 ), the second lightness value (L * _i2 ), and the saturation h. The details will be described below.

The brightness adjusting section 35 includes a first brightness value (L * _i1 ) obtained from the first brightness calculating section 32 and a second brightness calculating section 33.
Based on the second lightness value obtained from (L * _i2), calculates a brightness adjusting vector vL * _i. Specifically, vL * _i is calculated by the following equation.

VL * _i = L * _i2− L * _i1 Subsequently, the brightness adjusting section 35 obtains the saturation h from the saturation calculating section 34. Then, the lightness L * _i adjusted based on the saturation h and the lightness adjustment vector vL * _i previously obtained is calculated. Specifically, by solving the following equation, L * _i
Is calculated.

[0077] _{L * i = L * i1 +} vL * i × h As apparent from this equation, the brightness adjusting unit 35 in accordance with the saturation h decreases (approaches the achromatic), the first lightness value (L * Adjust the brightness to approach _i1 ). vice versa,
As the saturation h increases (becomes brighter),
Adjust the brightness to approach the second brightness value (L * _i2 ).

The brightness adjusting section 35 adjusts the brightness L * _i adjusted in this way and the input color i obtained from the first brightness calculating section 32.
The hue component values (a * _i , b * _i ) are output to the saturation adjustment unit 36. Since the saturation adjustment unit 36 and the output system color reproduction unit 37 are already well-known, detailed description will be omitted.

As described above, in the color image processing apparatus according to the first embodiment, the first lightness value (L * _i1 ) within the output system lightness range in which the lightness ratio is stored without depending on the hue.
And a second lightness value (L * _i2 ) within the output system lightness range in consideration of the lightness of the maximum saturation point of the output system depending on the hue, and the saturation h of the input color becomes small ( (Approaching achromatic color) to the first lightness value (L * _i1 )
Conversely, the lightness is adjusted so as to approach the second lightness value (L * _i2 ) as the saturation h increases (becomes vivid colors). Therefore, no matter what the color reproduction range of each output device is, it is necessary to reproduce high-saturation colors in the output system if the input colors are high saturation, without breaking the lightness balance near achromatic colors. Can be. Therefore, high-quality color reproduction is possible for both artificial color graphics using a large number of primary colors and natural images such as photographs.

In the present embodiment, the brightness is adjusted according to the saturation. However, the lightness may be adjusted in accordance with the saturation of the input color and further some other index value reflecting the saturation value.

The upper limit value and the lower limit value of the brightness adjustment range are as follows:
The present invention is not limited to the first brightness value and the second brightness value described above. The brightness value obtained by a method different from the above-described method may be adopted as the upper limit value and the lower limit value.

Embodiment 2 The color image processing apparatus of Embodiment 2 adjusts the lightness in accordance with the saturation and hue of the input color, so that any hue of a highly saturated image can be reproduced more naturally. The biggest feature is that it can be done.

First, the outline of the main features of this apparatus will be described with reference to FIG. Details of each part will be described later for each part.

The color space used in the present invention may be any color space that can be separated into lightness and hue information, but in the present embodiment, CIE L *
The description will be made using the a * b * color space.

This color image processing apparatus includes an input color space information storage unit 30, an output color space information storage unit 31, a first brightness calculation unit 32, a second brightness calculation unit 33, a saturation calculation unit 34, and a brightness adjustment unit 35. , Saturation adjustment section 36 and output color reproduction section 3
7 is provided. Input color space information storage unit 30
Has white CIE XYZ values (X
_iw , Y _iw , Z _iw ), white lightness value (L * _iw ), black lightness value (L * _ik ), and a 3 × 3 matrix (MTX [3] [3] for converting RGB values into XYZ values ]) Are stored. The output color space information storage unit 31 stores a white lightness value (L * _ow ) and a black lightness value (L) in the output color space.
* _ok ), cyan (L * _c , a * _c , b * _c ), magenta (L
* _m , a * _m , b * _m ), yellow (L * _y , a * _y , b * _y ), red (L
* _r , a * _r , b * _r ), blue (L * _b , a * _b , b * _b ), green (L
* _g , a * _g , b * _g ) CIE L at 100% printing
* a * b * values are stored.

Although not shown in FIG. 1, the output color space information storage 31 of the second embodiment stores
Yellow, yellow-green, green-cyan, cyan-blue, blue-magenta,
Hue-specific lightness adjustment vector coefficients are stored for each of the six magenta-red sections. The hue-based lightness adjustment vector coefficient is a value in the range of 0 to 1 that defines the lightness adjustment range by the lightness adjustment unit 35 for each hue, and is in accordance with the reproducible chroma range of the output system and the input system. The value is set. For example, when the lightness of the color having the highest saturation in the input system is extremely different from the lightness of the color having the highest saturation in the output system, the hue-based lightness adjustment vector coefficient is reduced.
If the difference between the two lightnesses is small, increase the value. For example, for a hue in which the difference between the lightness of the color with the highest saturation in the input system and the lightness of the color with the highest saturation in the output system exceeds a predetermined threshold value, this hue-specific lightness adjustment vector coefficient A value smaller than 1 is set so as not to exceed the threshold value of the brightness difference.

Data input from outside (R of input color i)
The GB value (R _i , G _i , B _i ) is calculated by the first lightness calculation unit 32,
It is input to the second lightness calculator 33 and the saturation calculator 34.

The first lightness calculator 32 calculates the RGB values of the input color i.
Based on the value _{(R i, G i, B} i), and calculates the CIE L * a * b * values _{(L * i1, a * i} , b * i). This L * _i1 (hereinafter referred to as “first brightness value (L * _i1 )”) is exclusively
This is determined from the viewpoint that the lightness of the input color i falls within the lightness range of the output system, and does not consider the saturation. That is, the first lightness value (L * _i1 )
The brightness ratio is stored independently of the hue. In particular,
The first lightness value (L * _i1 ) is obtained by _calculating the ratio of the difference between the lowest lightness and the highest lightness in the input system and the difference between the lowest lightness and the lightness of the input color by the minimum lightness and the highest lightness in the output system. Is a brightness value calculated to be stored for the difference (see FIG. 4). Various data necessary for the calculation are stored in the input color space information storage unit 30 and the output color space information storage unit 3.
I get it from 1. The first lightness calculator 32 outputs the CIE L * a * b * values (L * _i1 , a * _i , b * _i ) thus obtained to the lightness controller 35.

The second lightness calculating section 33 calculates the RGB values of the input color i.
Based on the values (R _i , G _i , B _i ), a second lightness value (L
* Calculate _i2 ). The second lightness value (L * _i2 ) is a value in the output system lightness range determined in consideration of the lightness of the maximum saturation point of the output system depending on the hue. Specifically, the second
Lightness value (L * _i2) is the lightness L * _ims and up to the input color i of the same hue lightness L * _iw most having high saturation color ims input color i of the same hue (or minimum lightness L * _ik ), the ratio of the difference between the lightness L * _i of the input color i and the highest lightness L * _iw (or the lowest lightness L * _ik ) of the same hue as the input color i, and the input Difference between the lightness L * _{oms of the} color oms having the highest saturation in the same hue as the output color corresponding to the color i and the highest lightness L * _ow (or the lowest lightness L * _ok ) in the same hue as the output color. And the ratio of the difference between the lightness of the output color corresponding to the input color i and the highest lightness L * _ow (or the lowest lightness L * _ok ) of the same hue as that of the output color. Of the output color (see FIG. 5). Various data necessary for the calculation are obtained from the input color space information storage unit 30 and the output color space information storage unit 31. The second brightness calculating unit 33 outputs the obtained second brightness value (L * _i2 ) to the brightness adjusting unit 35.
Although not shown in FIG. 1, the second lightness calculation unit 33 according to the second embodiment includes an output color space information storage unit 31.
, And obtains a hue-based lightness adjustment vector coefficient of the input color i, and outputs this as kvL * to the lightness adjustment unit 35 (see FIG. 9).

The saturation calculator 34 calculates a saturation h indicating the degree of vividness of the input color i based on the RGB values (R _i , G _i , B _i ) of the input color i. Various data necessary for the calculation are obtained from the input color space information storage unit 30 and the output color space information storage unit 31. The saturation calculator 34 outputs the calculated saturation h to the brightness controller 35.

The brightness adjuster 35 calculates the saturation h calculated by the saturation calculator 34 and the CIE calculated by the first brightness calculator 32.
The L * a * b * value (L * _i1 , a * _i , b * _i ), the second lightness value (L * _i2 ) obtained from the second lightness calculator 33, and the hue-based lightness adjustment vector coefficient kvL * Based on CIE L * a
The * b * values (L * _i , a * _i , b * _i ) are obtained, and these are calculated by the saturation adjusting unit 3.
Output to 6. That is, the brightness adjusting unit 35 adjusts the brightness within a predetermined brightness adjustment range (lower limit value, upper limit value) according to the saturation h so that the brightness of the input color i falls within the brightness range of the output system. As the saturation h of the input color i decreases (ie, approaches the achromatic color), the brightness is adjusted so as to approach the lower limit. Conversely, as the saturation h of the input color i increases (that is, becomes more vivid), the brightness is adjusted so as to approach the upper limit. Note that the saturation h = 0
, L * _i = lower limit, and if saturation h = 1, L * _i
= The upper limit. In this case, the brightness adjustment range (lower limit value, upper limit value) itself is finely set according to the hue of the input color using the hue-specific brightness adjustment vector coefficient kvL *. The lower limit of the brightness adjustment range is the first brightness value (L *
_i1 ). The upper limit is the hue-based lightness adjustment vector coefficient k
Depending on vL *, it is changed between the first lightness value (L * _i1 ) and the second lightness value (L * _i2 ). When the hue-based lightness adjustment vector coefficient kvL * is 1, the upper limit of the lightness adjustment range is the second lightness value (L * _i2 ). When the hue-based lightness adjustment vector coefficient kvL * is 0, the upper limit of the lightness adjustment range is also the first lightness value (L * _i1 ).

The saturation adjusting section 36 adjusts the CIE L * to make the saturation of the input color i fall within the saturation range of the output system.
The saturation of the a * b * value (L * _i , a * _i , b * _i ) is adjusted by a known method, and the result is set as the CIE L * a * b * value (L * _i ,
a * _i , b * _i ).

The output color reproduction section 37 outputs the CIEL * a * b * value (L) of the input color i within the color reproduction range of the output system.
* _i , a * _i , b * _i ) are converted into output color signals that can be output by a known method.

As described above, the color image processing apparatus can naturally reproduce even a highly saturated image by adjusting the lightness according to the saturation h. Moreover, the second embodiment
In the color image processing apparatus described above, since the adjustment range of lightness is also changed according to the hue, an image can be reproduced more naturally even in an output system in which the reproducible saturation range is largely different depending on the hue.

The outline of the main features has been described above.

In the second embodiment, the “brightness adjustment range” referred to in the claims is a section defined by a first brightness value, a second brightness value, and a hue-based brightness adjustment vector coefficient. It is. The “adjustment range determining unit” includes an input color space information storage unit 30, a first lightness calculation unit 32,
This is realized by the second lightness calculation unit 33 and the output color space information storage unit 31. The “index value” corresponds to the saturation h. The “saturation evaluation unit” is realized by the saturation calculator 34 and the output color space information storage 31. “Brightness adjusting means” corresponds to the brightness adjusting unit 35. The “upper limit setting unit” is realized by the input color space information storage unit 30, the output color space information storage unit 31, the second brightness calculation unit 33, and the brightness adjustment unit 35. The “adjustment coefficient” corresponds to a hue-based lightness adjustment vector coefficient. The “storage unit” corresponds to the output color space information storage unit 31. The “calculating means” includes the second brightness calculating unit 33 and the brightness adjusting unit 3
5 is realized. "Lower limit setting means"
Input color space information storage unit 30, Output color space information storage unit 31
And the first brightness calculation unit 32. However, since the above-described units operate in close cooperation with each other, the correspondence described here is not strict.

[0097] Hereinafter, each of the above-described parts will be described with reference to FIGS.
Each part will be described in detail with reference to FIG.

First, the details of the first lightness calculator 32 in FIG. 1 will be described.

The first lightness calculator 32 calculates the first lightness value (L * _i1 ). As described above, the first lightness value (L * _i1 ) is a value that preserves the lightness ratio independently of the hue and is within the output system lightness range. The details will be described below.

The first lightness calculating section 32 stores the RGB → XYZ conversion matrix (MTX) in the input color space information storage section 30.
[3] [3]), the RGB values (R _i ,
G _i , B _i ) are converted to CIE XYZ values by a known method. Further, referring to the white CIE XYZ values (X _iw , Y _iw , Z _iw ) of the input color space information storage unit 30, the CIE L * a * b * values (L * _i , a * _i , b
* _i ).

Subsequently, the first lightness calculating section 32 outputs the white lightness (L * _iw ) and the black lightness (L * _ik ) from the input color space information storage section 30 and the output color space information storage section. 3
The brightness of white (L * _ow ) and the brightness of black (L
* _ok ) get. Then, a first lightness value (L * _i1 ) is calculated using these (see FIG. 4). First lightness value (L *
_i1 ) is a distance (brightness difference) [L * _ow−
L * _ok] and the distance ratio of (lightness _{difference) [L * i 1 -L *} ok] is the distance (lightness _{difference) [L * iw -L * ik} ] a distance (lightness difference)
It is the same as the ratio of [L * _i -L * _ik ] and within the output system brightness range. Specifically, L * _i1 is calculated by solving the following equation.

L * _i1 = ((L * _i −L * _ik )) ÷ (L * _iw −
L * _ik )) × (L * _ow− L * _ok ) + L * _ok Finally, the first lightness calculator 32 calculates the CIE L * a * b * values (L * _i1 , a *) _i , b * _i ) are output to the brightness controller 35.

Next, the details of the second lightness calculating section 33 in FIG. 1 will be described with reference to FIGS. 9, 5, 6, and 8. FIG.

The second brightness calculation section 33 calculates the second brightness value (L * _i2 ). As already mentioned, this second lightness value (L * _i2 ) depends on the hue,
This value is within the output system lightness range in consideration of the lightness of the maximum saturation point of the output system. The details will be described below.

The second lightness calculating section 33 includes a maximum chroma RGB value calculating section 110, an RGB → LAB converting section I111, and RGB.
→ LAB conversion unit II112, output system maximum saturation point calculation unit 11
3 and a second brightness calculation core unit 114.

Data input from outside (R of input color i)
The GB values (R _i , G _i , B _i ) are input to the maximum saturation RGB value calculation unit 110, the RGB → LAB conversion unit II 112, and the output system maximum saturation point calculation unit 113.

The maximum saturation RGB value calculation section 110 calculates the input color i based on the RGB values (R _i , G _i , B _i ) of the input color i.
And RGB values (R _ims , G _ims , B _ims ) indicating the color ims having the same hue and the highest saturation in the input system. The specific calculation method is as follows (see FIG. 8).

The maximum chroma RGB value calculating section 110 calculates the RGB value of the input color i based on the RGB values (R _i , G _i , B _i ).
Order the GB. For general description, the one having the largest value is represented by UP _i , the one having the next largest value is represented by MIDLE _i , and the one having the smallest value are represented by LOW _i . At this time, the RGB values (R _ims , G _ims , B _ims ) of the color ims having the same hue and the highest saturation are as follows.

UP _ims 1.0 MIDLE _ims (1.0 ÷ (UP _i −LOW _i )) ×
(MIDLE _i -LOW _i ) LOW _ims 0.0 where the RGB values (R _i , G _i , B _i ) are normalized to 0.0 to 1.0 as shown in FIG. .

For example, UP → R, MIDLE → G, LO
If W → B, the RGB values (R _ims , G _ims , B _ims ) of the color ims having the same hue and the highest saturation are as follows.

R _ims = 1.0 G _ims = (1.0 ÷ (R _i −B _i )) × (G _i −B _i ) B _ims = 0.0 The maximum saturation RGB value calculation section 110 The RGB values (R _ims , G _ims , B _ims ) of the color ims having the same hue as the input color i and having the highest saturation in the input system are obtained as described above.
Output to the LAB conversion unit I111.

The RGB → LAB conversion unit I111 firstly
R of the color ims having the same hue as the input color i and having the highest saturation in the input system, which is input from the maximum saturation RGB value calculation unit 110
The GB values (R _ims , G _ims , B _ims ) are _converted to the first lightness calculating unit 3.
2 (FIG. 1) to convert to CIE L * a * b * values (L * _ims , a * _ims , b * _ims ). Then, L * _ims among them is output to second brightness calculation core section 114.

The RGB → LAB conversion unit II 112 performs the same operation as the CIE L * based on the RGB values (R _i , G _i , B _i ) of the input color i by the same operation as the first brightness calculation unit 32 (FIG. 1).
The a * b * value (L * _i , a * _i , b * _i ) is calculated. Then, the obtained (L * _i , a * _i , b * _i ) is converted into the second brightness calculation core unit 114.
The output is output to the output system maximum saturation point calculation unit 113.

The output system maximum saturation point calculation unit 113 outputs the cyan (L * _c , a * _c , b * _c ) and magenta (L * _m , a *) in the output color space from the output color space information storage unit 31. _m , b
* _m ), yellow (L * _y , a * _y , b * _y ), red (L * _r , a * _r , b
* _r ), blue (L * _b , a * _b , b * _b ), green (L * _g , a * _g , b
* _g ) CIE L * at 100% printing for each
Get a * b * value. Also, as described above, RGB → L
The CIE L * a * b of the input color i from the AB conversion unit II 112
* Value (L * _i , a * _i , b * _i ) is obtained.

Then, the output system maximum saturation point calculation unit 113
Means that the input color i is red, yellow, green, cyan,
It is determined which of the hue sections formed by blue and magenta falls. In the description here, as shown in FIG. After the hue section is determined, the output-system maximum chroma point calculation unit 113 obtains the hue-based lightness adjustment vector coefficient kvL * of the corresponding hue from the output color space information storage unit 31 and holds it.

Next, the output system maximum chroma point calculation unit 113 calculates
Calculate the hue component values (a * _oms , b * _oms ) at the intersection of the straight line connecting the input color and the origin and the straight line connecting red and yellow (this intersection corresponds to the position of the color oms) on the hue plane. I do.
The intersection can be calculated by solving the following simultaneous equations.

B * _oms = (b * _i ÷ a * _i ) × a * _oms b * _oms = ((b * _r− b * _y ) ÷ (a * _r− a * _y )) × a * _oms
+ (A * _r * b * _y- a * _y * b * _r ) ÷ (a * _r- a * _y ) Subsequently, the output-system maximum chroma point calculation unit 113 calculates the distance between red and yellow on the hue plane. , The ratio of the intersection-red distance calculated above is calculated. If this ratio is S, S can be calculated by the following equation.

S = (distance between oms and red) ÷ (distance between yellow and red) Next, using the calculated ratio S, red lightness (L * _r ), and yellow lightness (L * _y ), Calculates the intersection om
The brightness of s (L * _oms ) is calculated.

The output-system maximum chroma point calculation unit 113 calculates L * _oms = S × L * _y + (1.0−S) × L * _r .
A color om having the same hue as the input color i and the highest saturation in the output system
CIE L * a * b * value of s (L * _oms , a * _oms , b * _oms )
Can be calculated.

The output system maximum chroma point calculation unit 113 calculates the calculated L * _oms and the hue-based lightness adjustment vector coefficient kvL * in the second
Output to the brightness calculation core unit 114.

The second lightness calculating core unit 114 firstly outputs the lightness of the input white (L * _iw ) and the lightness of the black input (L * _iw ).
* _ik ) is obtained from the input color space information storage unit 30. Also,
The lightness (L * _ims ) of the color ims having the same hue as the input color i and the highest saturation in the input system from the RGB → LAB conversion unit _I111
Get. Further, the color component values (a * _i , b * _i ) of the input color i are obtained from the RGB → LAB conversion unit II 112. If the lightness (L * _i ) of the input color i is larger than the lightness (L * _ims ) of ims, the distance between ims-white (lightness difference) in the lightness axis direction and the distance between ims-input color i ( The ratio is calculated as S1 (see FIG. 5A). Conversely, the brightness of the input color i (L * _i ) is the brightness of ims (L * _ims )
If smaller, the distance between ims-black (lightness difference) and the distance between ims-input color i (lightness difference) in the lightness axis direction
Is calculated, and this is defined as S1.

Subsequently, the second lightness calculation core unit 114 outputs the lightness of the output system white (L * _ow ) and the lightness of the output system black (L * _ow ).
_ok ) is obtained from the output color space information storage unit 31. The output system maximum saturation point calculation unit 113 outputs the lightness (L) of the color oms having the same hue as the input color i and having the highest saturation in the output system.
* _oms ) and the hue-based lightness adjustment vector coefficient kvL *. Then, by performing a proportional calculation using the previously calculated distance ratio S1, a second lightness value (L) within the output system lightness range is obtained.
* _i2 ) (see FIG. 5B). Specifically, L * _i2 is calculated by solving the following equation.

[0123] L * _i> L * In the case of _{ims L * i2 = S1 × L} * oms + (1.0-S1) × L * ow L * In the case of _{i ≦ L * ims L * i2} = S1 × L * _oms + (1.0−S1) × L * _ok The second lightness calculator 33 calculates L * _i2 obtained as described above.
And the hue-based brightness adjustment vector coefficient kvL * is output to the brightness adjustment unit 35.

Next, details of the saturation calculator 34 of FIG. 1 will be described with reference to FIGS.

The saturation calculator 34 is for calculating the saturation h indicating the vividness of the input color i. As shown in FIG. 3, the saturation calculator 34 includes a maximum saturation RGB value calculator 50, an RGB → LAB converter I51, and an RGB → LA
A B conversion unit II 52 and a saturation calculation core unit 53 are provided.

Data input from outside (R of input color i)
The GB values (R _i , G _i , B _i ) are input to the maximum saturation RGB value calculation unit 50 and the RGB → LAB conversion unit II 52.

The RGB → LAB conversion section II 52 outputs the input color i
CIE L * a * based on the RGB values (R _i , G _i , B _i ) of the first lightness calculation unit 32 (FIG. 1).
The b * value (L * _i , a * _i , b * _i ) is calculated. Then, the calculated (L * _i , a * _i , b * _i ) is output to the saturation calculating core unit 53.

The maximum chroma RGB value calculating section 50 calculates the input color i
Based on the RGB values (R _i , G _i , B _i ) of
By the same operation as the B value calculation unit 110 (FIG. 9), RGB values (R _ims , G _ims , B _ims ) indicating the color ims having the same hue as the input color i and having the highest saturation in the input system are calculated. This is output to the RGB → LAB conversion unit I51. Next, R
The GB → LAB conversion unit I51 outputs the RGB values (R _ims , G _{i ms} , G _{i ms) of} the color ims having the same hue as the input color i and having the highest saturation in the input system, which is input from the maximum saturation RGB value calculation unit 50. B
_ims ) is _converted to a CIE L * a * b * value (L * _ims , a * _ims , b * _ims ) by the same operation as the first lightness calculation unit 32 (FIG. 1).
And outputs it to the saturation calculation core unit 53.

The saturation calculation core unit 53 firstly outputs RGB →
Input from LAB conversion section I51, the input color i of the same hue at and most having high saturation color hue component values ims input system and _{(a * i ms, b *} ims), from RGB → LAB converter unit II52 Based on the input hue component values (a * _i , b * _i ) of the input color i, the saturation of each color is calculated by a known method. Here, the saturation of ims is Sims, and the saturation of i is Si.

Next, the saturation calculation core unit 53 converts the RGB →
The brightness (L * _ims ) of _ims is obtained from the LAB conversion unit I51. Further, the brightness (L * _i ) of the input color i is obtained from the RGB → LAB converter II 52. Further, the input color space information storage unit 3
From 0, the lightness of the input system white (L * _iw ) and the lightness of the input system black (L * _ik ) are obtained. Then, the brightness of the input color i (L *
_{If i} ) is greater than the lightness of ims (L * _ims ), the distance of ims-white in the lightness axis direction (lightness difference) is:
The ratio between ims and the distance (brightness difference) of the input color i is calculated, and this is defined as S1 (see FIG. 7). Conversely, if the lightness (L * _i ) of the input color i is smaller than the lightness (L * _ims ) of ims, the ims-black distance (lightness difference) in the lightness axis direction and the ims-input color i The ratio with respect to the distance (brightness difference) is calculated and set as S1.

Thereafter, the saturation calculating core unit 53 performs a proportional calculation using the previously calculated saturation Sims,
The saturation Sims ′ corresponding to the lightness of i is calculated. Specifically, Sims' is calculated by solving the following equation.

Sims' = S1 × Sims Finally, the saturation calculating core unit 53 calculates the saturation h by solving the following equation.

H = Si ÷ Sims' The saturation calculating section 34 calculates the saturation h obtained as described above.
Is output to the brightness adjusting unit 35 (see FIG. 1).

Next, details of the brightness adjusting section 35 of FIG. 1 will be described.

The lightness adjusting section 35 controls the first lightness value (L
* _i1 ), the second lightness value (L * _i2 ), the saturation h, and the hue-specific lightness adjustment vector coefficient kvL * to adjust the lightness. The details will be described below.

The brightness adjusting section 35 includes a first brightness value (L * _i1 ) obtained from the first brightness calculating section 32 and a second brightness calculating section 33.
Based on the second lightness value obtained from (L * _i2), calculates a brightness adjusting vector vL * _i. Specifically, vL * _i is calculated by the following equation.

VL * _i = L * _i2 −L * _i1 Subsequently, the brightness adjustment section 35 receives the hue-based brightness adjustment vector coefficient kvL * from the second brightness calculation section 33 and the saturation calculation section 34 obtains the saturation degree. get h. And this saturation h
Then, the brightness L * _i adjusted based on the hue-based brightness adjustment vector coefficient kvL * and the brightness adjustment vector vL * _i obtained in advance is calculated. Specifically, L * _i is calculated by solving the following equation.

L * _i = L * _i1 + kvL * × vL * _i × h The brightness adjusting unit 35 adjusts the brightness L * _i thus adjusted and the hue component of the input color i obtained from the first brightness calculating unit 32. The values (a * _i , b * _i ) are output to the saturation controller 36.

Saturation adjusting section 36 and output system color reproducing section 37
Is already well known, and a detailed description thereof will be omitted.

As described above, in the second embodiment,
By using the hue-specific coefficients prepared in advance, it is possible to adjust to what extent a color close to the output system maximum chroma color is reproduced for a high chroma color in each hue. Therefore, even in an output device having a special color reproduction range, a color with high saturation can be reproduced in the output system if the input color is high chroma without breaking the lightness balance in the vicinity of achromatic colors. Therefore, high-quality color reproduction is possible for both artificial color graphics using a large number of primary colors and natural images such as photographs.

[0141]

As described above, according to the color image processing method and apparatus of the present invention, if the input color is high chroma, a color with high chroma is output in the output system without breaking the lightness balance near achromatic color. It is possible to reproduce high-quality color for both artificial color graphics using a large number of primary colors and natural images such as photographs.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an overall configuration of a color image processing device according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a second brightness calculating unit.

FIG. 3 is a block diagram illustrating a configuration of a saturation calculator.

FIG. 4 is a diagram illustrating a principle of obtaining a brightness value within an output system brightness range.

FIG. 5A is a diagram showing a method for obtaining S1, and FIG.
FIG. 7 is a diagram showing a method for obtaining a lightness value (L * _i2 ) within the output system lightness range.

FIG. 6 is a diagram showing a hue plane.

FIG. 7 is a diagram showing a method for obtaining S1.

FIG. 8 shows maximum saturation RGB values (R _ims , G _ims , B _ims )
FIG. 5 is a diagram showing a method for obtaining the.

FIG. 9 is a block diagram illustrating a configuration of a second brightness calculating unit according to Embodiment 2 of the present invention.

FIG. 10 is a color plan view showing a conventional color image processing method.

FIG. 11 is a diagram showing a conventional color image processing method.

[Explanation of symbols]

30 input color space information storage unit, 31 output color space information storage unit, 32 first lightness calculation unit, 33 second lightness calculation unit, 34 saturation calculation unit, 35 lightness adjustment unit,
36 saturation adjustment section, 37 output color reproduction section, 40
Maximum saturation RGB calculation unit, 41 RGB → LAB conversion unit
I, 42 RGB → LAB conversion section II, 43 output system maximum saturation point calculation section, 44 second brightness calculation core section, 50
Maximum saturation RGB calculation unit, 51 RGB → LAB conversion unit I, 52 RGB → LAB conversion unit II, 53 saturation calculation core unit, 110 Maximum saturation RGB calculation unit, 1
11 RGB → LAB conversion unit I, 112 RGB → L
AB converter II, 113 output system maximum chroma point calculator, 1
14 The second brightness calculation core unit.

Claims (13)

[Claims] 1. An adjustment range setting for setting a range for adjusting brightness (hereinafter referred to as a "brightness adjustment range") in a color image processing apparatus for outputting brightness after adjusting brightness of an arbitrary input color according to an output system. Means, saturation evaluation means for obtaining an index value reflecting the saturation of the input color, and brightness adjustment means for setting the brightness value of the output color within the brightness adjustment range according to the index value. Characteristic color image processing device. 2. The method according to claim 1, wherein the adjusting range setting means includes: an input system brightness range, an output system brightness range, an input color brightness,
Based on the lightness of the maximum chroma color in the input system at the same hue as the input color, and the lightness of the maximum chroma color in the output system at the same hue as the output color corresponding to the input color, the upper limit of the lightness adjustment range is 2. The color image processing apparatus according to claim 1, further comprising an upper limit value setting unit for setting. 3. The method according to claim 1, wherein the adjustment range setting unit includes a lower limit value setting unit that sets a lower limit value of the brightness adjustment range based on a brightness range of an input system, a brightness range of an output system, and brightness of an input color. The color image processing apparatus according to claim 1 or 2, wherein 4. The color image processing apparatus according to claim 1, wherein said adjustment range setting means changes said brightness adjustment range according to the hue of an input color. 5. The adjustment range setting means includes: a hue of an input color, a lightness range of an input system, a lightness range of an output system,
The brightness adjustment range based on the brightness of the input color, the brightness of the maximum chroma color in the input system at the same hue as the input color, and the brightness of the maximum chroma color in the output system at the same hue as the output color corresponding to the input color. 5. The color image processing apparatus according to claim 4, further comprising an upper limit value setting unit that sets an upper limit value of the color image. 6. An upper limit value setting unit, comprising: a storage unit storing a table defining an adjustment coefficient set for each hue, an input color hue adjustment coefficient, an input system lightness range, and an output system lightness. The brightness based on the range, the brightness of the input color, the brightness of the maximum chroma color in the input system at the same hue as the input color, and the brightness of the maximum chroma color in the output system at the same hue as the output color corresponding to the input color. 6. The color image processing apparatus according to claim 5, further comprising: an operation unit for obtaining an upper limit value of the adjustment range. 7. The adjustment range setting unit includes a lower limit value setting unit that sets a lower limit value of the brightness adjustment range based on a brightness range of an input system, a brightness range of an output system, and a brightness of an input color. The color image processing apparatus according to claim 4, 5 or 6, wherein 8. A color image processing method in which the brightness of an arbitrary input color is adjusted according to an output system and then output, wherein a range for adjusting the brightness (hereinafter referred to as “brightness adjustment range”) is set. A color image processing method comprising: obtaining an index value reflecting the saturation of the output color; and setting a lightness value of the output color within the lightness adjustment range according to the index value. 9. The lightness of an input color and the same hue as the input color with respect to the difference between the lightness of the color with the highest saturation in the same hue as the input color and the highest lightness or the lowest lightness in the same hue as the input color. And the ratio of the difference between the highest lightness or the lowest lightness, the lightness of the color with the same hue as the output color corresponding to the input color, and the highest lightness or the lowest lightness with the same hue as the output color For the difference between the brightness of the output color corresponding to the input color and the ratio of the difference between the highest brightness or the lowest brightness in the same hue as the output color, a brightness value in which both ratios match is obtained, 9. The color image processing method according to claim 8, wherein the upper limit of the brightness adjustment range is set. 10. The ratio of the difference between the minimum brightness and the maximum brightness in the input system and the difference between the minimum brightness and the brightness of the input color is stored for the difference between the minimum brightness and the maximum brightness in the output system. 10. The color image processing method according to claim 9, wherein a brightness value is obtained and the calculated brightness value is set as a lower limit value of the brightness adjustment range. 11. A color image processing method for adjusting the brightness of an arbitrary input color according to an output system and outputting the adjusted color, wherein a range in which the brightness is adjusted (hereinafter referred to as a “brightness adjustment range”) is set to a hue of the input color. An index value reflecting the saturation of the input color, and setting the brightness value of the output color within the brightness adjustment range according to the index value. 12. The lightness of an input color and the same hue as the input color with respect to the difference between the lightness of the color with the highest saturation in the same hue as the input color and the highest lightness or the lowest lightness in the same hue as the input color. And the ratio of the difference between the highest lightness or the lowest lightness, the lightness of the color with the highest saturation in the same hue as the output color corresponding to the input color, and the highest lightness or the lowest lightness in the same hue as the output color And the ratio of the difference between the lightness of the output color corresponding to the input color and the highest lightness or the lowest lightness in the same hue as the output color is determined. 12. The color image processing method according to claim 11, wherein a value obtained by integrating coefficient values set according to the hue of the color is set as an upper limit value of the lightness adjustment range. 13. The ratio of the difference between the minimum brightness and the maximum brightness in the input system and the difference between the minimum brightness and the brightness of the input color is stored for the difference between the minimum brightness and the maximum brightness in the output system. 13. The color image processing method according to claim 11, wherein a brightness value is obtained and the calculated brightness value is set as a lower limit value of the brightness adjustment range.