JP4541772B2 - Color conversion method, profile creation method and apparatus - Google Patents

Description

  The present invention relates to a color conversion method, a profile creation method, and a profile creation apparatus.

  Since the color characteristics of image input / output devices vary from model to model, when color image data is used between different models, there is a problem that the reproduced colors do not match. As a method for solving this problem and unifying the color reproduction of color images between different apparatuses, a color management system (hereinafter referred to as CMS) is used.

  In CMS, the same color image is reproduced by a plurality of image input / output devices (for example, a color copier, a color monitor, a digital camera, and a color printer), so that a common color for mutually converting the color signals of the devices is used. A space (hereinafter referred to as a color mapping color space) is used. Color matching between devices is realized by converting the color signal of the input system device into the color signal of the output system device so that the color signals in the color mapping color space match. Here, the input system device indicates a device that is a color matching target. For example, when the color of the color printer B is matched with the color of the color printer A, the color printer A is the input system device and the color printer B is the output system. It becomes a device. As the color mapping color space, a colorimetric value space such as CIEXYZ or CIELAB is generally used. That is, in general, in CMS, the color signal of the input system device is converted into the color signal of the output system device so that the colorimetric values match.

  However, particularly in the low saturation region, even if the colorimetric values are simply combined, a good reproduced image may not be obtained, which is a problem of CMS. For example, when ink or toner is used for the white signal in printing by a color printer, even if the colorimetric value matches that of the input system device, it is perceived as “color cast” and the impression is bad. Therefore, the white color normally printed by a color printer is the color of the image recording medium (printing paper) itself, and no ink or toner is used. That is, the white color of the color printer needs to be reproduced with a color unique to the output system device regardless of the colorimetric value of the input system device.

  In addition, since the gray of medium brightness also determines the print color so that the chromaticity continuously changes from white specific to the output system device to black, the color unique to the output system device regardless of the colorimetric value of the input system device. It is desirable to reproduce with. Furthermore, in order to make the maximum use of the dynamic range of the device, black is also required to be printed in the maximum density color unique to the output system device or a color close to the maximum density color regardless of the colorimetric value of the input system device. is there. That is, the conventional method using the colorimetric value space for the color mapping color space has a problem that good reproduction cannot be obtained in a low saturation region.

  In order to solve the above problems, improvement of the color mapping color space has been studied. For example, an improved color mapping color space is proposed in which the isoluminance plane of the colorimetric value space is translated so that the gray color signal including white and black of the device becomes a color signal indicating an achromatic color (saturation = 0). Has been. FIG. 12 is a diagram showing an example of the relationship between such an improved color mapping color space and the CIELAB color space, which is a colorimetric value space. In the figure, the horizontal axis represents a * in the CIELAB color space, and the vertical axis represents the same b *. In addition, a point P in the figure indicates a gray of the apparatus, a point P ′ indicates an achromatic color in the colorimetric value space, 5001 indicates the color reproduction range of the apparatus in the CIELAB color space, and 5002 indicates in the improved color mapping color space. Indicates the color reproduction range of the device. As shown in the figure, the color signal in the improved color mapping color space is obtained by translating the color signal in the CIELAB color space by a vector PP ′. The above conversion (translation) is performed for all brightness values. In the improved color mapping color space, grays having different colorimetric values unique to each device can be represented by points on the same straight line, and grays having the same brightness can be handled by the same color signal. Such a technique for preventing color cast by moving a gray line is described in Patent Document 1, for example.

JP 2001-326826 A

  However, when the improved color mapping color space described above is used, the reproducibility of the low saturation portion is improved, but the improvement of the low saturation portion affects the chromatic color, and conversely, the reproducibility of the chromatic color is deteriorated. There is a problem of doing. For example, important colors such as skin color are desired to be reproduced with the same colorimetric value regardless of the device, but in the improved color mapping color space, colors having the same colorimetric value are represented by different color signals depending on the device. . Therefore, even if the color signals are converted so that the color signals match in the improved color mapping color space, a good reproduced image cannot be obtained.

  The present invention has been made in view of the above problems, a color conversion method capable of achieving both low color saturation reproducibility and chromatic color reproducibility, and a method of creating profile data used in the color conversion method, and To provide an apparatus.

In order to achieve the above object, a color conversion method of the present invention is a color conversion method for converting a color signal of an image output device, and is a first method for converting a color signal of an image output device into a color signal of a uniform color space. And a second conversion step for converting a color signal in the uniform color space into a color signal in the color mapping color space. The second conversion step is (1) after the conversion in the first conversion step. Is output outside the low saturation region, the color signal after the conversion in the first conversion step is output as the color signal after the conversion in the second conversion step, and (2) the first When the color signal after the conversion by the conversion process exists in the low saturation region, the signal of the image output device among the color signals after the conversion by the first conversion process is used as the signal after the conversion by the second conversion process. The gray line color signal is output as a signal converted to an achromatic color signal in a uniform color space. Of the color signals after conversion in the conversion process, color signals other than the gray line signal of the image output device output a signal converted and output to another color signal in the low saturation region, and the low saturation region outputs the image. It is defined as an area including a color signal having the same brightness as the color signal after the conversion in the first conversion step and a color signal indicating an achromatic color in a uniform color space on the gray line of the apparatus .
The above-described object is a color conversion method for converting the color signal of the image output device, the first conversion step of converting the color signal of the image output device into the color signal of the uniform color space, and the uniform color space. A second conversion step of converting the color signal into a color signal in the color mapping color space, and the second conversion step is (1) the color signal after the conversion in the first conversion step is outside the low saturation region. The color signal after the conversion by the first conversion step is output as the color signal after the conversion by the second conversion step, and (2) the color signal after the conversion by the first conversion step is low. If it exists in the saturation region, the intersection of the color signal after the conversion in the first conversion step and the straight line passing through the color signal having the same lightness and the low saturation region is defined, and the first conversion step The converted color signal is converted into a color signal between the intersection and the color signal indicating an achromatic color in a uniform color space. A color signal having the same brightness as the color signal after the conversion by the first conversion step on the gray line of the image output device; It is also achieved by the color conversion method of the present invention characterized by being defined as a region including a color signal indicating an achromatic color in a uniform color space.

The above-described object is a profile creation device that creates profile data for converting color signals of an image output device, and converts the discrete color signals of the image output device into color signals of a uniform color space. A profile is obtained from correspondence information between the first conversion unit, the second conversion unit that converts the color signal of the uniform color space into the color signal of the color mapping color space, and the discrete color signal and the color signal of the color mapping color space. Profile generating means to be created, and the second converting means is : (1) when the color signal after the conversion by the first converting means exists outside the low saturation region, the second converting means When the color signal after the conversion by the first conversion means is output as the color signal after the conversion by (2), and (2) the color signal after the conversion by the first conversion means exists in the low saturation region, As a signal after conversion by the second conversion means Among the color signals after the conversion by the first conversion means, the gray line color signal of the image output device outputs a signal converted into an achromatic color signal in a uniform color space, and the color after the conversion by the first conversion means. Of the signals, the color signals other than the gray line signal of the image output device output a signal converted and output to another color signal in the low saturation region, and the low saturation region is the second signal on the gray line of the image output device. The profile creating apparatus of the present invention is defined as an area including a color signal having the same lightness as the color signal after conversion by one conversion means and a color signal indicating an achromatic color in a uniform color space. Achieved.
Another object of the present invention is to create a profile data for creating profile data for converting color signals of the image output apparatus, which converts the discrete color signals of the image output apparatus into color signals of a uniform color space. A profile is obtained from correspondence information between the first conversion unit, the second conversion unit that converts the color signal of the uniform color space into the color signal of the color mapping color space, and the discrete color signal and the color signal of the color mapping color space. Profile generating means to be created, and the second converting means is: (1) when the color signal after the conversion by the first converting means exists outside the low saturation region, the second converting means When the color signal after the conversion by the first conversion means is output as the color signal after the conversion by (1), and (2) the color signal after the conversion by the first conversion means exists in the low saturation region, Color signal after conversion by 1 conversion means The intersection of the straight line passing through the color signal having the same brightness and the low saturation region is defined, and the color signal after conversion by the first conversion means is defined between the color signal indicating an achromatic color in the uniform color space and the intersection. And is output as a color signal after conversion by the second conversion means, and the low saturation region has the same lightness as the color signal after conversion by the first conversion means on the gray line of the image output device. It is also achieved by the profile creating apparatus of the present invention characterized by color conversion characterized by being defined as an area including a color signal having a color signal and a color signal indicating an achromatic color in a uniform color space.

Another object of the present invention is to provide a profile creation method for creating profile data for converting color signals of an image output apparatus, which converts discrete color signals of an image output apparatus into color signals of a uniform color space. A profile is obtained from the correspondence information between the first conversion step, the second conversion step of converting the color signal of the uniform color space into the color signal of the color mapping color space, and the discrete color signal and the color signal of the color mapping color space. A profile creation step to be created, and the second conversion step is (1) the second conversion step when the color signal after the conversion by the first conversion step exists outside the low saturation region. When the color signal after the conversion by the first conversion step is output as the color signal after the conversion by (2), and (2) the color signal after the conversion by the first conversion step exists in the low saturation region, As a signal after conversion by the second conversion step Among the color signals after the conversion in the first conversion step, the gray line color signal of the image output device outputs a signal converted into an achromatic color signal in the uniform color space, and the color after the conversion in the first conversion step. Of the signals, the color signals other than the gray line signal of the image output device output a signal converted and output to another color signal in the low saturation region, and the low saturation region is the second signal on the gray line of the image output device. According to the profile creation method of the present invention, the region is defined as a region including a color signal having the same brightness as the color signal after the conversion in one conversion step and a color signal indicating an achromatic color in a uniform color space. Achieved.

  Further, the above object is to provide a program for causing a computer device to execute the color conversion method or profile creation method of the present invention, a program for causing the computer device to function as the profile creation device of the present invention, or a computer storing any one of these programs. It is also achieved by a readable recording medium.

  With such a configuration, according to the present invention, it is possible to achieve both the reproducibility of the low saturation portion and the reproducibility of the chromatic color.

Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the drawings.
<First Embodiment>
<CMS>
First, an outline of a CMS as an embodiment of a color conversion apparatus according to the present invention will be described with reference to FIG. As shown in FIG. 11, in the CMS according to the present embodiment, an input system profile conversion unit 3001, a color mapping unit 3002, an output system profile conversion unit 3003, an input system profile storage unit 3004, and an output system profile storage unit 3005. The color signal RGB of the input system device is converted into the color signal R′G′B ′ of the output system device.

  The input system device profile conversion unit 3001 converts the color signal RGB of the input system device into the color signal Lab of the color mapping color space using, for example, the input system device profile stored in the input system device profile storage unit 3004. The input system device profile used here is, for example, a look-up table (hereinafter referred to as LUT) that holds output color signals Lab related to discrete input color signals RGB, and the input system device profile conversion unit 3001 converts the LUT into the LUT. An arbitrary input color signal RGB is converted into a corresponding output color signal Lab by a known interpolation method used.

  The color mapping unit 3002 converts the input color signal Lab into a color signal L′ a′b ′ that can be reproduced by the output system device. When the color reproduction ranges of the input system device and the output system device are the same, the color mapping unit 3002 generally outputs the input color signal Lab as it is. When the color reproduction ranges of the input system device and the output system device are different, the color mapping unit 3002 converts the input color signal Lab into the output color signal L′ a′b ′ by a known color reproduction range compression method or expansion method. . For example, the output system profile conversion unit 3003 uses the output system profile stored in the output system profile storage unit 3005 to convert the color signal L′ a′b ′ of the color mapping color space into the color signal of the output system. Convert to R'G'B '. The output system device profile used here is, for example, an LUT that holds the input color signal L′ a′b ′ related to the discrete output color signal R′G′B ′, and the output system device profile conversion unit 3003 An arbitrary input color signal L′ a′b ′ is converted into a corresponding output color signal R′G′B ′ by a known search and interpolation method using the LUT.

  Hereinafter, as the first embodiment, in such a CMS, the color signals (Lab and L′ a′b ′) of the color mapping color space are obtained from the color signals (RGB and R′G′B ′) of the apparatus. The color conversion method will be described. As a second embodiment, a method for creating profiles stored in the input system profile storage unit 3004 and the output system profile storage unit 3005 in such a CMS will be described. As a third embodiment, a creation method for interactively adjusting and creating a profile created in the second embodiment will be described.

<Color conversion method>
FIG. 1 is a schematic diagram for explaining a color conversion method according to the first embodiment of the present invention, and shows an iso-lightness surface in a CIELAB color space as an example of a uniform color space. In the figure, point P is a point indicating gray specific to the image output apparatus, point O is a point indicating achromatic color, 101 is the outermost contour of the low saturation region R including point P and point O, and point B is the region concerned. It is an arbitrary point on the outermost contour 101 of R. At this time, in the color conversion method of the present embodiment, for example, the color indicated by the point A on the line segment BP is changed to the color indicated by the point D on the line segment BO so that the ratio of PB: PA and OB: OD becomes equal. It is characterized by converting. Further, it is characterized in that colors outside the region R are not converted (input color signals are output as they are).

  Due to these characteristics, the color conversion method of the present embodiment converts gray P having different colorimetric values depending on the image output device so as to be the same color signal indicated by the point O, and colors outside the region R such as skin color. Can convert the color of the same colorimetric value into the same color signal.

<Color conversion procedure>
Next, the color conversion procedure of this embodiment is shown using the flowchart of FIG.
First, in step S201, initial setting processing including acquisition of parameters, a color conversion table, a gray line table, and the like, which will be described later, is performed. In step S202, the color signal RGB of the image output apparatus is acquired. In step S203, the color signal RGB acquired in step S202 is converted into a color signal Lab ((L *, a *, b *) = (L, a, b)) in the colorimetric color space. The conversion is performed by a known interpolation method using the color conversion table acquired in step S201. The color conversion table is, for example, a grid point ({R, G, B} = {0, 0, 0}, {0, 0, 32}, {0, 0, 64} of an 8-bit RGB color signal) , ..., {0,0,255}, {0,32,0}, ..., {255,255,255}) are output by the image output device, and this output image Is a table storing the colorimetric values Lab. The color signal Lab converted in step S203 will be described as the color signal A below.

  In step S204, the color signal P on the gray line of the image output apparatus at the lightness of the color signal A is obtained. The color signal P is calculated using the gray line table acquired in step S201. Details will be described later. Next, in step S205, it is determined whether or not the color signal A is a color signal in the low saturation region R. If the color signal is in the low saturation region R, the process proceeds to step S206, where the color signal A is outside the low saturation region R. If it is a color signal, the process proceeds to step S210. As described above, the low saturation region R is a low saturation region including the color signal P and the achromatic color signal O.

  If the color signal A is a color signal in the low saturation region R, the color signal P is compared with the color signal A in step S206, and if both are the same color signal, the process proceeds to step S211. If they are not the same color signal, the process proceeds to step S207. Next, in step S207, the color signal B indicated by the intersection is obtained from the straight line connecting the color signal P and the color signal A and the outermost contour of the low saturation region R. When there are two intersections, the distance between the color signal A and the color signal P is obtained for each intersection, and the intersection closer to the color signal A than the color signal P (distance with the color signal A <color signal P The color signal B is defined as the distance between and the intersection point.

  In step S208, the color signal A is converted by the conversion function for converting the color signal on the line segment BP connecting the color signal B and the color signal P into the color signal on the line segment BO connecting the color signal B and the color signal O. To obtain an output color signal D ((L *, a *, b *) = (L, a ′, b ′)), and the process proceeds to step S209.

  On the other hand, if the color signal A is a color signal outside the region R in step S205, the color signal A is set as it is in the output color signal D (without conversion) in step S210, and the process proceeds to step S209. move on. If the color signal P and the color signal A are the same color signal in step S206, the color signal O is set as the output color signal D in step S211, and the process proceeds to step S209. Finally, in step S209, the output color signal D set in step S208, step S210, or step S211 is output.

Hereinafter, the processing content of each process is demonstrated in detail.
<Low chroma region R>
FIG. 3 is a schematic diagram for explaining an example of the low saturation region R used in the present embodiment, and shows an iso-lightness surface in the CIELAB color space. The low saturation region R in the present embodiment is defined by an ellipse whose main axis is a straight line passing through the color signal P indicating gray and the achromatic color signal O of the image output apparatus. In the figure, the horizontal axis indicates a * in the CIELAB color space, and the vertical axis indicates the same b *. In the figure, point P is a point indicating the color signal P, point O is a point indicating the color signal O, 3001 is the outermost region of the region R, θ is an angle formed by the horizontal axis a * and the straight line OP, and a point G is Indicates the center of the ellipse. From the coordinates (Pa, Pb) of the point P and the coordinates (0, 0) of the point O, the coordinates (Ga, Gb) of the point G are obtained by the following equations.
Ga = Pa / 2 (1)
Gb = Pb / 2 (2)

Further, the distance E between the point O and the point P is obtained by the following equation.
E = √ (Pa ² + Pb ² ) (3)
When α and β are the parameters acquired in step S201, the lengths L1 and L2 of the main axis of the ellipse are obtained by the following equations.
L1 = E · α (4)
L2 = L1 · β (5)

  The parameter α is a value of 1 or more (for example, 1.8). If the value α is large, the change of the color signal included in the region R becomes gradual, but the range affected by the conversion is widened. Conversely, when the value is small, the range affected by the conversion is narrowed, but the color signal included in the region R may change abruptly, resulting in poor gradation. The parameter β is a parameter for determining an elliptical shape. If the value of the parameter β is large, the range affected by the conversion is widened, and if the value is small, the color signal in the region R may change abruptly, resulting in a gradation failure.

  Further, as shown in FIG. 3, an st coordinate system is considered, which includes a vector OP and a vector obtained by rotating the vector OP by 90 degrees counterclockwise with the point G as the origin. In FIG. 3, conversion from (a *, b *) coordinates to (s, t) coordinates is performed by the following equation.

However, M is a matrix given by the following equation.

Here, θ is an angle shown in FIG. 3 and is given by the following equation.
θ = atan (Pb / Pa) (8)
Also, conversion from (s, t) coordinates to (a *, b *) coordinates is performed by the following equation.

<Calculation method of color signal P>
Next, the calculation method of the color signal P in S204 will be described in detail. FIG. 4 is a diagram showing an example of the gray line table acquired in step S201 of FIG. As shown in the figure, the gray line table of the present embodiment is a table storing colorimetric values CIELAB relating to discrete gray levels GL. The gray level GL is a color signal having the same R, G, and B signals. For example, the value of the gray level 32 (GL = 32) is (R, G, B) = (32, 32, 32). The colorimetric value when the image is output by the image output device is stored. Using the gray line table, the values of the chromaticity coordinates a * and b * at an arbitrary lightness L can be obtained by a known interpolation method. That is, for the color signal P, the gray chromaticity coordinates corresponding to the lightness value L of the color signal A are calculated by a known interpolation method based on the gray line table acquired in step S201, and the chromaticity coordinates and lightness are calculated. Can be generated by the value L.

<Internal / external determination method>
Next, the inside / outside determination method performed in step S205 of FIG. 2 will be described in detail. In this embodiment, in order to determine whether or not the color signal A is within the region R, the following determination process is performed. That is, first, the chromaticity coordinates (a, b) of the color signal A are converted into coordinate values (S, T) in the (s, t) coordinate system using the equation (6). Next, the following evaluation function Q is calculated.
Q = √ ((2S / L1) ² + (2T / L2) ² ) (10)
Here, L1 and L2 are the lengths of the principal axes of the ellipses given by the equations (4) and (5), respectively. When the value of the evaluation function Q in Expression (10) is 1, the color signal A (S, T) is on an ellipse. If the Q is less than 1, the color signal A is in the ellipse, that is, in a low saturation region. If it is within the R region and Q is greater than 1, the color signal A is outside the ellipse, that is, outside the low saturation region R. In addition, when it is necessary to process the color signal A on the ellipse as belonging to either the ellipse or the outside of the ellipse, it can be arbitrarily set which one belongs. Therefore, in the following description, the color signal A on the ellipse is handled as a signal inside or outside the area depending on the setting. However, in terms of ease of subsequent processing, the color signal A on the ellipse is preferably handled as a color signal outside the region.

<Calculation method of color signal B>
Next, the calculation method of the color signal B in step S207 of FIG. 2 will be described in detail. The color signal B is an intersection of a straight line connecting the color signal P and the color signal A and the outermost contour of the low saturation region R. When the coordinate values of the color signal P and the color signal A in the (s, t) coordinate system are Pst (Ps, Pt) and Ast (As, At), respectively, on the straight line connecting the color signal P and the color signal A The color signal (S, T) satisfies the following expression.
T = (At−Pt) / (As−Ps) × (S−Ps) + Pt (11)

Further, the color signal (S, T) on the outermost contour in the low saturation region R satisfies the following expression because the value of the evaluation function Q is 1 in the above expression (10).
√ ((2S / L1) ² + (2T / L2) ² ) = 1 (12)
The coordinate value Bst (S, T) of the color signal B in the (s, t) coordinate system is obtained by solving simultaneous equations of the above equations (11) and (12). When there are two solutions of the simultaneous equations and there are two intersections, the distance between the above Pst and Ast is obtained for each intersection, and the intersection closer to Ast than Pst is defined as Bst.

  That is, in the present embodiment, the following calculation process is performed to obtain the color signal B. That is, first, the chromaticity coordinates of the color signal P and the color signal A are converted into coordinate values in the (s, t) coordinate system using the equation (6). Next, the coordinate value of the color signal B in the (s, t) coordinate system is calculated by solving the simultaneous equations of the above equations (11) and (12). Finally, the (s, t) coordinate system is converted from the (s, t) coordinate system to the (a *, b *) coordinate system by the above equation (9), and the coordinate value of the color signal B in the (a *, b *) coordinate system is calculated.

The color signal B can also be obtained by the following method. A color signal on a straight line Lpa passing through the color signal P = (L, Pa, Pb) and the color signal A = (L, a, b) is defined as a color signal F = (L, U, V). At this time, the b * value V of the color signal F is obtained from the a * value U of the color signal F using the following equation (13).
V (U) = (b−Pb) / (a−Pa) × (U−Pa) + Pb (13)

  That is, the color signal F on the straight line Lpa can be uniquely expressed by the value of U, and this is represented by F (U) = (L, U, V (U)). Of the color signals F (U1) and F (U2) corresponding to two U values U1 and U2 having a sufficiently small difference, one is in the region R and one is outside the region R. At some point, the color signal B is provided by one of the color signals (eg, F (U1)).

FIG. 5 is a flowchart showing a second calculation procedure of the color signal B in the present embodiment.
First, in step S501, initial values of a U value Umin corresponding to a color signal in the region R and a U value Umax corresponding to a color signal considered to be outside the region R are set. For example, Pa is set for Umin, and Umax is set to 10 if Pa <a, and is set to -10 if Pa> a. Next, in step S502, it is determined whether or not the color signal corresponding to Umax is within the region R by the inside / outside determination method using equation (10). If within the region, the process proceeds to step S503, and outside the region. If there is, the process proceeds to step S504. Here, the color signal corresponding to Umax is given by (L, Umax, V (Umax)). Note that V (Umax) is obtained using equation (13).

If it is determined in step S502 that the color signal corresponding to Umax is within the area, Umax is corrected so that the color signal corresponding to Umax is outside the area R in step S503, and the process returns to step S502. Umax is corrected by the following equation, for example.
Umax after correction = Umax before correction × 2 (14)
If it is determined in step S502 that the region is out of the region, in step S504, an average value Uave of Umax and Umin is obtained by the following equation.
Uave = (Umax + Umin) / 2 (15)

  Next, in step S505, it is determined by the inside / outside determination method whether or not the color signal F (Uave) corresponding to Uave is within the region R. If it is within the region, the process proceeds to step S507. The process proceeds to S506. If it is determined in step S505 that the region is out of the region, in step S506, Umax is set and updated in Umax, and the process proceeds to step S508. If it is determined in step S505 that it is within the area, in step S507, Umin is set and updated in Umin, and the process proceeds to step S508. In step S508, the difference between Umax and Umin is calculated. If the absolute value is less than the predetermined value SH, the process proceeds to step S509, and if it is equal to or greater than SH, the process returns to step S504. If the absolute value of the difference between Umax and Umin is less than the predetermined value SH in step S508, the color signal B is given by (L, Umin, V (Umin)), for example. In step S509, the color signal B is output.

<Conversion function>
Next, the conversion function used for converting the color signal A to the color signal D in step S208 of FIG. 2 will be described in detail. As described above, the conversion function is a function for converting the color signal on the line segment BP to the color signal on the line segment BO, and the color signal A (L, a, b), which is the color signal on the line segment BP, is converted. The color signal D (L, a ′, b ′) on the line segment BO is converted. FIG. 6 is a diagram illustrating an example of a conversion function that can be used in the present embodiment. The horizontal signal is a color signal on a line segment BP whose input value is an input value, and the vertical axis is a color signal on a line segment BO whose output value is an output value. Indicates. The conversion function shown in FIG. 6 is linear conversion, and is converted so that the ratio between the distance between the line segment BP and the distance between the line segments BA is equal to the ratio between the distance between the line segment BO and the distance between the line segments BD. That is, when the conversion function shown in FIG. 6 is used, the color signal D is obtained by the following equations (16) and (17).
a ′ = (a−Ba) / (Pa−Ba) × (Oa−Ba) + Ba (16)
b ′ = (b−Bb) / (Pb−Bb) × (Ob−Bb) + Bb (17)
Here, the coordinates of the point O are (L, Oa, Ob) and the coordinates of the point B are (L, Ba, Bb).

  As described above, the color conversion method according to the present embodiment is the color conversion method for converting the color signal of the image output apparatus into the color signal of the color mapping color space, and the color included in the predetermined low saturation region. Converts the colorimetric value color (gray) that varies depending on the device to the same color signal in the color mapping color space, and in other areas including chromatic colors such as skin color, the same regardless of the device. It is possible to convert the colors of the colorimetric values so as to be the same color signal even in the color matching color space.

  As a result, “color cast” in CMS can be suppressed and the dynamic range of the apparatus can be utilized to the maximum, and chromatic colors such as skin color can be reproduced with colorimetrically equal colors. Become.

  In the embodiment, CIELAB is used as the color space. However, other uniform color spaces may be used. More preferably, a CAM color space can be used.

<Second Embodiment>
In the present embodiment, a profile creation device that creates a profile of an image output device used in CMS using the color conversion method described in the first embodiment will be described.

<Functional configuration>
FIG. 7 is a block diagram illustrating a functional configuration example of the profile creation device according to the present embodiment. As shown in FIG. 7, the profile creation apparatus 700 of this embodiment includes a data input unit 701, a colorimetric value conversion table storage unit 702, a parameter storage unit 703, an interpolation calculation unit 704, a gray line table storage unit 705, a data output. 706, a color signal generation unit 707, a low saturation area conversion unit 708, and an output profile storage unit 709.

  The colorimetric value conversion table storage unit 702 inputs and stores the colorimetric value conversion table of the image output apparatus via the data input unit 701. The profile creation apparatus according to the present embodiment creates a profile (profile stored in the input system profile storage unit 3004) for converting the color signal of the image output apparatus into a color mapping color signal in the CMS shown in FIG. 11, for example. To do.

  As described in the first embodiment, the colorimetric value conversion table is an LUT of colorimetric values indicating the color reproduction characteristics of the image output apparatus. For example, an RGB color signal ({R , G, B} = {0,0,0}, {0,0,32}, {0,0,64}, ..., {0,0,255}, {0,32,0}, ..., {255, 255, 255}) is output by the image output device and obtained by measuring the color of the output image. The parameter storage unit 703 stores parameters (α in Expression (4) and β in Expression (5)) for determining the shape of the low-saturation region R in advance or acquired via the data input unit 701. And store. The interpolation calculation unit 704 uses the colorimetric value conversion table of the image output device stored in the colorimetric value conversion table storage unit 702 to make known the output color of the image output device corresponding to an arbitrary input RGB color signal. Calculate and output by interpolation method.

  The gray line table storage unit 705 generates a discrete gray line color signal by the color signal generation unit 707, and the interpolation calculation unit 704 calculates the output color of the image output device corresponding to the gray line color signal. Is stored. The gray line table is, for example, the table shown in FIG. 4 described in the first embodiment. The low saturation area converting unit 708 includes a colorimetric value conversion table of the image output apparatus stored in the colorimetric value conversion table storage unit 702, a gray line table stored in the gray line table storage unit 705, and a parameter storage unit. Using the parameters stored in 703, the discrete RGB color signals forming the LUT generated by the color signal generation unit 707 are converted based on the color conversion method described in the first embodiment, and the output profile Store in the storage unit 709. The discrete RGB color signals constituting the LUT are, for example, 8-bit 9-slice grid point color signals ({R, G, B} = {0,0,0}, {0,0,32}, {0 , 0,64}, ..., {0,0,255}, {0,32,0}, ..., {255,255,255}). The color signal stored in the output profile storage unit 709 is output via the data output unit 706.

<Profile creation procedure>
Next, the profile creation procedure in the present embodiment will be described using the flowchart of FIG.
First, in step S801, initial setting processing is performed. Specifically, parameters for determining the shape of the low saturation region R and the colorimetric value conversion table of the image output device are acquired and stored in the parameter storage unit 703 and the colorimetric value conversion table storage unit 702, respectively. Do. In step S 802, a gray line table is created using the colorimetric value conversion table acquired in step S 801 and stored in the gray line table storage unit 705. In step S803, an RGB color signal of 8-bit 9-slice grid points constituting the profile LUT is generated.

  Subsequently, in order to obtain the color signal of the color mapping color space corresponding to the RGB color signal by the method described in the first embodiment, the flowchart shown in FIG. 2 is executed from step S203, and the RGB color signal is converted to the RGB color signal in step S209. After obtaining the color signal D of the corresponding color mapping color space, the process proceeds to step S804.

  In step S804, the color signal of the color mapping color space obtained in step S209 is stored in the output profile storage unit 709. In step S805, it is determined whether or not the color signals of the corresponding color mapping color space have been stored for all the color signals constituting the LUT of the profile. If all the color signals have been stored, step S806 is performed. If not, the process returns to step S803. Finally, in step S806, the output profile stored in the output profile storage unit 709 is output.

  As described above, the profile creation apparatus according to the present embodiment creates a profile of an image output apparatus used in CMS using the color conversion method described in the first embodiment. The CMS stores and uses the profile created by the profile creation device of the present embodiment in the input system profile storage unit 3004, so that the gray line of the input system device is different from the gray line of the output system device in terms of colorimetry. In addition, the color signal of the input system device is changed to the color signal of the output system device so that the skin color and other colors outside the predetermined low saturation region are reproduced with the same colorimetric values as the input system device. It becomes possible to convert.

  In this embodiment, the gray line table is created using the colorimetric value conversion table stored in the colorimetric value conversion table storage unit 702, but may be input via the data input unit 701 separately.

■ <Third Embodiment>
The third embodiment is characterized in that a function for interactively adjusting the size of the low saturation region R is added to the profile creation apparatus described in the second embodiment. Since the functional configuration and profile creation procedure of the profile creation apparatus according to the present embodiment are the same as those of the second embodiment, a description thereof will be omitted, and only characteristic functions in the present embodiment will be described.

<Parameter setting UI>
The profile creation apparatus according to the present embodiment provides a UI (user interface) for interactively setting parameters stored in the parameter storage unit 703. This function is realized as a part of the function of the data input unit 701 in FIG. 7, for example, and is presented to the user in the step of acquiring parameters in step S801 in FIG.

  FIG. 9 is a diagram illustrating an example of a UI provided by the profile creation apparatus according to the present embodiment, which includes a parameter setting unit 901, a low saturation region confirmation unit 902, an OK button 903, and a cancel button 904.

  Such a UI is presented to the user by displaying it on a display device if the profile creation device is implemented using a general-purpose computer device commercially available as a personal computer, for example. Then, the user operates the UI using an input device typically used for UI operation, such as a keyboard and a mouse. The operation result is reflected in the UI in real time, and the user can interactively determine the setting value while checking the operation result.

  The provision of the user setting function using such a UI (GUI) itself is a well-known technique in computer software, and is not directly related to the essence of the present embodiment, so that further description is omitted.

  In FIG. 9, a parameter setting unit 901 includes controls for setting parameters. In the example of FIG. 9, a slide bar 905 for specifying the size of a low saturation region and a low saturation region confirmation unit 902 Has a slide bar 906 for designating the brightness of the equal brightness surface to be displayed.

  The slide bar 905 is used for setting the parameter α in Expression (4). When the bar is moved to the right, the low saturation region (region R) is increased, and when the bar is moved to the left, the low saturation region is decreased. Corresponding to the movement of the slide bar 905, the size of the low saturation region outermost contour 907 displayed on the low saturation region confirmation unit 902 changes. The slide bar 906 is used to set the lightness of the equal lightness surface displayed in the low saturation area confirmation unit 902. The lightness increases when the bar is moved to the right, and the lightness decreases when the bar is moved to the left. Corresponding to the movement of the slide bar 906, the brightness displayed on the low saturation area confirmation unit 902 changes.

  The low saturation area confirmation unit 902 is a graph showing the isoluminance surface of the color space, and includes an outermost contour 907 of the low saturation area, a color chromaticity point 908 on the gray line of the apparatus, and a point 909 indicating an achromatic color. Illustrated. When the OK button 903 is pressed, a parameter value determined by the position of the slide bar is set and stored in the parameter storage unit 703. When the cancel button 904 is pressed, the setting is ignored.

  FIG. 10 is a diagram showing another UI example of the parameter setting unit 901. In order to specify the text box 1001 for directly specifying the parameter α in the equation (4) with a numerical value and the parameter β in the equation (5). Text box 1002 and a text box 1003 for designating the brightness to be displayed in the low saturation area confirmation unit 902.

  As described above, the parameter α is a value of 1 or more, and when the value is large, the change of the color signal in the low saturation region becomes gradual, but the range affected by the conversion is widened. On the contrary, if the value is small, the range affected by the conversion is narrowed, but the color signal in the low saturation region may change suddenly, resulting in poor gradation. The parameter β is a parameter for determining an elliptical shape. If the value of the parameter β is large, the range affected by the conversion is widened, and if the value is small, the color signal in the low saturation region may change suddenly, resulting in poor gradation. When the OK button 903 is pressed, a parameter value determined by the position of the slide bar is set and stored in the parameter storage unit 703. When the cancel button 904 is pressed, the setting is ignored.

  When the cancel button 904 is pressed, for example, prestored initial values are used as the values of α and β. In the example of FIG. 9, since β is not specified, for example, an initial value is used as the value of β even when the OK button is pressed.

  According to the profile created by the profile creation device of the present embodiment, the color signal in the low saturation region and the color signal outside the low saturation region are the same as the profile created by the profile creation device of the second embodiment. The color conversion method of the first embodiment for performing different conversions can be implemented. Then, according to the profile creation device of the present embodiment, the user can interactively set the size of the low saturation region.

<Other embodiments>
A software program that realizes the functions of the above-described embodiments is supplied directly from a recording medium or to a system or apparatus having a computer that can execute the program using wired / wireless communication. The present invention includes a case where an equivalent function is achieved by a computer executing the supplied program.

  Accordingly, the program code itself supplied and installed in the computer in order to implement the functional processing of the present invention by the computer also realizes the present invention. That is, the computer program itself for realizing the functional processing of the present invention is also included in the present invention.

  In this case, the program may be in any form as long as it has a program function, such as an object code, a program executed by an interpreter, or script data supplied to the OS.

  As a recording medium for supplying the program, for example, a magnetic recording medium such as a flexible disk, a hard disk, a magnetic tape, MO, CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-R, DVD- There are optical / magneto-optical storage media such as RW, and non-volatile semiconductor memory.

  As a program supply method using wired / wireless communication, a computer program forming the present invention on a server on a computer network, or a computer forming the present invention on a client computer such as a compressed file including an automatic installation function A method of storing a data file (program data file) that can be a program and downloading the program data file to a connected client computer can be used. In this case, the program data file can be divided into a plurality of segment files, and the segment files can be arranged on different servers.

  That is, the present invention includes a server device that allows a plurality of users to download a program data file for realizing the functional processing of the present invention on a computer.

  In addition, the program of the present invention is encrypted, stored in a storage medium such as a CD-ROM, distributed to the user, and key information for decrypting the encryption for a user who satisfies a predetermined condition is provided via a homepage via the Internet, for example It is also possible to realize the program by downloading it from the computer and executing the encrypted program using the key information and installing it on the computer.

  In addition to the functions of the above-described embodiments being realized by the computer executing the read program, the OS running on the computer based on an instruction of the program is a part of the actual processing. Alternatively, the functions of the above-described embodiment can be realized by performing all of them and performing the processing.

  Furthermore, after the program read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion board or The CPU of the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments can also be realized by the processing.

It is a schematic diagram of a cross section of equal brightness for explaining a color conversion method according to an embodiment of the present invention. It is a flowchart which shows the color conversion procedure of 1st Embodiment. It is a schematic diagram of a cross section of equal brightness for explaining the low saturation region of the first embodiment. It is a figure which shows an example of the gray line table in 1st Embodiment. It is a flowchart which shows the acquisition procedure of the color signal B in 1st Embodiment. It is a figure which shows the color conversion function in 1st Embodiment. It is a figure which shows the function structure in 2nd Embodiment. It is a flowchart which shows the profile creation procedure in 2nd Embodiment. It is a figure which shows the parameter setting UI in 3rd Embodiment. It is a figure which shows the parameter setting UI in 3rd Embodiment. It is a figure explaining the outline | summary of CMS which concerns on embodiment of this invention. It is a schematic diagram of a cross section of equal lightness for explaining a conventional color conversion method.

Claims (7)

A color conversion method for converting a color signal of an image output device,
A first conversion step of converting a color signal of the image output device into a color signal of a uniform color space;
A second conversion step of converting the color signal of the uniform color space into a color signal of the color mapping color space,
Said second conversion step,
(1) When the color signal after the conversion by the first conversion step exists outside the low saturation region, the conversion by the first conversion step is performed as the color signal after the conversion by the second conversion step. The later color signal is output,
(2) When the color signal after the conversion by the first conversion step is present in the low saturation region, as the signal after the conversion by the second conversion step,
Of the color signals after the conversion in the first conversion step, the gray line color signal of the image output device outputs a signal converted into an achromatic color signal in the uniform color space,
Of the color signals after the conversion by the first conversion step, the color signals other than the gray line signals of the image output device output signals converted and output to other color signals in the low saturation region,
The low saturation region includes a color signal having the same brightness as the color signal after the conversion by the first conversion step on the gray line of the image output device, and a color signal indicating an achromatic color in the uniform color space. A color conversion method characterized by being defined as an area to be included . A color conversion method for converting a color signal of an image output device,
A first conversion step of converting a color signal of the image output device into a color signal of a uniform color space;
A second conversion step of converting the color signal of the uniform color space into a color signal of the color mapping color space,
Said second conversion step,
(1) When the color signal after the conversion by the first conversion step exists outside the low saturation region, the color signal after the conversion by the first conversion step is used as the color signal after the conversion by the second conversion step. and it outputs a color signal,
(2) When the color signal after the conversion by the first conversion step exists in the low saturation region, the color signal after the conversion by the first conversion step and the color signal having the same brightness are obtained. linear and the passing defines the intersection of the low-saturation region, a color signal between the color signal converted by the first conversion step, prior Symbol intersection and a color signal indicating the achromatic color in the uniform color space And output as a color signal after the conversion by the second conversion step,
The low saturation region includes a color signal having the same brightness as the color signal after the conversion by the first conversion step on the gray line of the image output device, and a color signal indicating an achromatic color in the uniform color space. color conversion how to characterized in that it is defined as an area including. A profile creation device for creating profile data for converting color signals of an image output device,
First conversion means for converting discrete color signals of the image output device into color signals of a uniform color space;
Second conversion means for converting the color signal of the uniform color space into a color signal of a color mapping color space;
Profile creation means for creating a profile from correspondence information between the discrete color signal and the color signal of the color mapping color space;
It said second conversion means,
(1) When the color signal after the conversion by the first conversion means exists outside the low saturation region, the color signal after the conversion by the second conversion means is converted by the first conversion means. The later color signal is output,
(2) When the color signal after the conversion by the first conversion means is present in the low saturation region, the signal after the conversion by the second conversion means is
Among the color signals converted by the first conversion means, the gray line color signal of the image output device outputs a signal converted into an achromatic color signal in the uniform color space,
Among the color signals after the conversion by the first conversion means, the color signals other than the gray line signal of the image output device outputs a signal converted and output to another color signal in the low saturation region,
The low saturation region includes a color signal having the same brightness as the color signal after conversion by the first conversion unit on the gray line of the image output apparatus, and a color signal indicating an achromatic color in the uniform color space. A profile creation device characterized by being defined as an area to be included . A profile creation device for creating profile data for converting color signals of an image output device,
First conversion means for converting discrete color signals of the image output device into color signals of a uniform color space;
Second conversion means for converting the color signal of the uniform color space into a color signal of a color mapping color space;
Profile creation means for creating a profile from correspondence information between the discrete color signal and the color signal of the color mapping color space;
It said second conversion means,
(1) When the color signal after the conversion by the first conversion means exists outside the low saturation region, the conversion by the first conversion means is performed as the color signal after the conversion by the second conversion means. The later color signal is output ,
(2) When the color signal after the conversion by the first conversion means is present in the low saturation region, the color signal after the conversion by the first conversion means and the color signal having the same brightness are obtained. linear and the passing defines the intersection of the low-saturation region, a color signal between the color signal converted by the first converting means, before Symbol intersection and a color signal indicating the achromatic color in the uniform color space And output as a color signal after conversion by the second conversion means,
The low saturation region includes a color signal having the same brightness as the color signal after conversion by the first conversion unit on the gray line of the image output apparatus, and a color signal indicating an achromatic color in the uniform color space. color conversion characteristics and to pulp profile creation device that is characterized in that it is defined as an area including. UI presenting means for presenting a user interface for allowing a user to set a parameter for controlling the size of the low saturation region;
Profile generation device according to claim 3 or claim 4, characterized by further comprising a region determination means for determining the low-saturation region based on the parameters set via the user interface. A profile creation method for creating profile data for converting color signals of an image output device,
A first conversion step of converting discrete color signals of the image output device into color signals of a uniform color space;
A second conversion step of converting the color signal of the uniform color space into a color signal of the color mapping color space;
A profile creating step of creating a profile from correspondence information between the discrete color signal and the color signal of the color mapping color space,
Said second conversion step,
(1) When the color signal after the conversion by the first conversion step exists outside the low saturation region, the conversion by the first conversion step is performed as the color signal after the conversion by the second conversion step. The later color signal is output,
(2) When the color signal after the conversion by the first conversion step is present in the low saturation region, as the signal after the conversion by the second conversion step,
Of the color signals after the conversion in the first conversion step, the gray line color signal of the image output device outputs a signal converted into an achromatic color signal in the uniform color space,
Of the color signals after the conversion by the first conversion step, the color signals other than the gray line signals of the image output device output signals converted and output to other color signals in the low saturation region,
The low saturation region includes a color signal having the same brightness as the color signal after the conversion by the first conversion step on the gray line of the image output device, and a color signal indicating an achromatic color in the uniform color space. A profile creation method characterized by being defined as an area to be included . Program for executing the steps of the profile creation method according to each step or claim 6 of the color conversion method according to any one of claims 1 to 2 to the computer.

Images