JP2003153026A - Color conversion method and image display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method of converting the colors, without giving visually a sense of incongruity, and an image display using the same. SOLUTION: The display comprises an image input means 71 for inputting an image signal of at least three color data, a setting means 72 for setting a goal color reproducing region, a setting means 73 for setting a visual coefficient suited for sight, a conversion means 74 for converting the color of the image signal fed from the image input means 71, based on the goal color reproducing region and the visual coefficient, and a display means 75 for displaying the color-converted image signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color conversion method for converting an image signal into a signal suitable for a target color reproduction range and an image display device using this color conversion method.

[0002]

2. Description of the Related Art As this type of conventional image processing method, for example, an image processing method as disclosed in Japanese Patent Laid-Open No. 2000-92337 can be mentioned. This Japanese Patent Laid-Open No. 2000-9
According to Japanese Patent Laid-Open No. 2337, the saturation cannot be sufficiently obtained in a portion having high lightness in the image represented by the digital image data only by making the gradation harder, and basically, the digital camera and the scanner are self-luminous. Since the digital image data has been acquired on the assumption that it will be displayed on a type CRT,
Due to the difference in color reproduction characteristics between the reflective print and the CRT,
In order to solve these problems, it is not possible to obtain a print image having desired color reproduction characteristics by simply increasing or decreasing the saturation (C *). It is an object of the present invention to provide an image processing method and apparatus capable of performing image processing as described above, and a computer-readable recording medium recording a program for causing a computer to execute the image processing method.

FIG. 9 is a schematic block diagram showing the configuration of a print system equipped with the image processing apparatus disclosed in Japanese Patent Laid-Open No. 2000-92337. This printing system uses image data S acquired by the digital camera 1.
Image processing means 2 for performing image processing on 0 to obtain processed image data S1 and printing means 3 for reproducing the processed image data S1 as a print image. The image processing means 2 includes a correction means 4 for performing density correction and color balance correction on the image data S0, and a gradation processing means 5 for performing gradation processing on the image data S0 processed by the correction means 4. And a color conversion processing means 6 for performing color conversion processing on the image data S0 processed by the gradation processing means 5.

In this printing system, an image processing method for subjecting digital image data to image processing for adjusting the saturation of each pixel of an original image represented by the digital image data to obtain processed image data, It is characterized in that the saturation of each pixel of the original image is weighted and adjusted by the hue and / or the brightness of each pixel of the original image. Specifically, the weight for the saturation is a function of the saturation of the original image (for example, CIE1976C *), the weight increases monotonously when C * is 0 to 40, and the weight monotonously decreases when C * is 50 or more. Thus, it is preferable to weight the saturation. The image output in FIG. 9 will be converted into the set weighted color. The above image processing method has an advantage that image processing can be performed on digital image data so as to obtain a desired saturation.

[0005]

However, since the above-mentioned conventional image processing method uses the weighting coefficient,
Although it is possible to output a preferable saturation, there is no guarantee that a visually preferable image will be obtained because its weighting coefficient does not correspond to the visibility, and it is difficult to realize color conversion with high visual evaluation. Further, the conventional out-of-gamut compression method has a problem that the visual effect is deteriorated because the weighting is performed to output a preferable saturation and not the weighting considering the visual characteristics.

The present invention has been made in order to solve the above problems, and when the color space reproduced by the image display device is converted into a target color space, a perception suitable for visual sense is obtained. By performing color conversion using a coefficient, it is possible to perform color conversion that is highly evaluated visually, and to round colors that can be reproduced in the target color reproduction range but cannot be reproduced by the display device. At this time, by using a color difference formula using a visual coefficient suitable for vision, it is possible to perform color conversion that does not give a visually uncomfortable feeling. Furthermore, when applying color matching between a plurality of image display devices, An object of the present invention is to provide a color conversion method and an image display device capable of reducing a visual color difference between matching image display devices.

[0007]

A color conversion method according to the present invention is a first color conversion method for determining a target color reproduction range in a color conversion method for converting a color space reproduced by an image signal into a target color space. Steps, a second step of determining a visual coefficient suitable for the visual sense, and a third step of performing color conversion based on the target color gamut and the visual coefficient.

Further, the color conversion is performed using a color difference formula to which the visual coefficient is applied. Further, the color space reproduced by the image signal is converted into a color space having hue, lightness, and saturation as variables, and the converted color space is color-converted by a color difference formula to which the visual coefficient is applied. is there. The visual coefficient is represented by a function of a variable other than the above variables. Further, when there is a color that cannot be reproduced in the target color reproduction range, the color outside the target color reproduction range is color-converted using the color difference formula to which the visual coefficient is applied and replaced with a reproducible color.

Further, the color conversion method according to the present invention comprises a step of subjectivity evaluation for obtaining an interval scale obtained from perceptual characteristics, and a statistical process for making the interval scale more reliable. And a step of calculating a visual coefficient, which means a visual correlation with respect to the three attributes of color, based on the highly reliable interval scale. Further, the calculation of the visual coefficient is performed based on the approximation of the interval scale.

Further, the image display device according to the present invention is
Image input means for inputting an image signal composed of at least three or more color data, target color reproduction area setting means for setting a target color reproduction area, visual coefficient setting means for setting a visual coefficient suitable for vision, and It is provided with color conversion means for performing color conversion of the image signal from the image input means on the basis of the target color reproduction area and the visual coefficient, and image display means for displaying the color-converted image signal.

Further, the target color reproduction area setting means calculates the target color reproduction area based on the characteristics of the target color reproduction area or the characteristics of the image display device. Further, the visual coefficient setting means changes the visual coefficient suitable for the sight according to the preference of the user when the visual coefficient suitable for the sight is selected. Further, when there is a color that cannot be reproduced in the target color reproduction area, the color conversion means performs color conversion of a color outside the target color reproduction area by using the color difference formula to which the visual coefficient is applied to obtain a reproducible color. It has a color gamut compression means for replacement.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.
It will be described with reference to the drawings. Embodiment 1. 1 is a block diagram showing an example of an entire circuit configuration used in a color conversion method according to a first embodiment of the present invention. In the figure, 11 is a target color gamut determining means, 12 is a visual coefficient determining means, and 13 is a color converting means. In the target color gamut determining means 11, a fixed target color gamut to be matched is set in advance according to the application, or is set by a user action from the target color gamut previously stored in the memory. It is decided by whether to do. Further, the visual coefficient determining means 12 is also set in advance according to the application similarly to the target color gamut determining means 11, or the coefficient value input by the user is read and set as the visual coefficient. The target color gamut and the visual coefficient are input to the color conversion means 13, and by the calculation of the target color gamut and the visual coefficient, the display device outputs the color that the user visually wants to finally output. The color gamut of is calculated and the output image signal is obtained.

Next, the operation will be described. The target color reproduction area determination means 11 determines the target color reproduction area according to the purpose. The target color gamut is at least the representative hue, R,
Includes G, B, C, M, Y pure colors and chromaticity data for white (W) and black (Bk). Pure colors are, for example, R (255,0,0), G in RGB signals.
(0,255,0), B (0,0,255), C (0,255,255), M (255,0,25)
5) and Y (255,255,0). The data described in the target color gamut is not limited to this, but the representative hue R,
It may include chromaticity data of gradation colors of several steps from Bk of G, B, C, M, Y to pure color and from highly saturated color to W. The target color reproduction area may be, for example, a standard color space of NTSC or sRGB, a color reproduction characteristic of a target image display device, or the like.

Further, these color gamuts are described in chromaticity such as L * a * b * color space or RGB color space, XYZ color space, YCbCr, YUV and the like. Alternatively, it may be described in a color space represented by three signals corresponding to a human pancreatic body using a color adaptation model in consideration of the influence of the environment on the visual sense. The optimum color space for color conversion by the color conversion means 13 performed after this is L * a * b *
Since it is a color space, the L * a * b * color space is used as a basic operation, but the other color spaces described above may be used.

The information on the selected color reproduction range is the above L * a * b *.
When the description is made in a color space other than the color space, the target color gamut determination means 11 may include a color space conversion means for converting to the L * a * b * color space. The color space conversion means converts to the L * a * b * color space using the color reproduction characteristics of the target color reproduction range. For example,
When converting from RGB color space, pure color of R, G, B and W, Bk
XYZ chromaticity data is used as the color reproduction characteristics of the reproduction range, the color mixture is converted to the XYZ color space using additive color mixing, and the XYZ color space is converted to the L * a * b * color space using a known conversion formula. .

The visual coefficient deciding means 12 decides the visual coefficient suitable for the visual sense so that the color transformation corresponding to the human visual sense can be performed at the time of the color transformation. The visual coefficient is composed of a number of coefficients corresponding to the number of axes of the color space in which the color gamut is described, that is, several spatial dimensions. For example, the L * a * b * color space is composed of three different coefficients. Also, each visual coefficient range is 0.
0 ≦ k ≦ 1.0. Or have a width comparable to that.

The color conversion means 13 is a target color reproduction area and visual coefficient determination means 12 determined by the target color reproduction area determination means 11.
The image signal displayed on the image display device corresponding to the color in the target color reproduction range is calculated based on the visual coefficient determined in step S3.
The color conversion unit 13 newly recalculates the target color gamut by using the visual coefficient, calculates the image color signal for reproducing the target color gamut, and the like, which is not described in the target color gamut. Means for interpolating the colors of. When the target color gamut is described in a color space different from that of the image signal, a color space conversion unit that converts the color space in which the target color gamut is described into the color space of the image signal may be provided. The color conversion means 13 will be specifically described.

For example, the visual coefficients may be weighting coefficients L1, a1, b1 for L * a * b *. Data of the target color gamut is multiplied by these coefficients, and the calculation result is set as a new target color gamut. The color of the reproduced image depends on the image color signal input to the image display device and the characteristics of the image display device to be displayed. In order to realize the reproduction of the target reproduction area, that is, the color space conversion means requires data indicating the characteristics of the image display device. At least the R, G, B pure colors of the image display device and the XYZ chromaticity data at W, Bk of the image display device are required for the characteristic data of the image display device. For example, if the target color gamut is represented by data in the L * a * b * color space, the image display device characteristics can be determined using a known formula that represents the relationship between the L * a * b * color space and the XYZ color space. Based on this, the data is converted back to XYZ color space data and converted to an image signal using additive color mixing. Other colors not described in the target color gamut are calculated by interpolation. Interpolation methods include linear interpolation and spline interpolation.

A color conversion method that has been generally developed is, for example, an image signal RGB1 corresponding to a target color gamut data, C1 (L1, a1, b1) in the L * a * b * color space. (R1, G1, B
There is a means to calculate 1). That is, the conversion method is such that the color signal data RGB1 capable of reproducing the color C1 is obtained, and RGB1 is output when the RGB1 ′ signal is input to the image display device. However, the L * a * b * color space is a color space that takes into account the visual characteristics, and its visual characteristics are exhibited compared to other color spaces, but it is not perfect and Deviations may occur. Especially in the blue region, the difference is remarkable.

As described above, in this embodiment, color conversion with a high visual effect can be realized by performing color conversion using the visual coefficient.

Embodiment 2. FIG. 2 is a block diagram showing a color conversion means used in the color conversion method according to the second embodiment of the present invention. In the figure, 21 is a minimum color difference calculation means, and 22 is a minimum color difference correspondence color signal calculation means.

Next, the operation will be described. When recalculating the target color gamut using the above visual coefficient, the minimum color difference calculating means 11 calculates the visual color difference using the color difference formula, and searches for a color having the minimum visual color difference other than 0. The minimum color difference correspondence color signal calculation means 12 calculates an image signal for displaying the retrieved color on the image display device.

For example, the color difference formula in the L * a * b * color space is expressed by the Euclidean distance. As shown in the following formula (1), the difference between each spatial axis is multiplied by the visual coefficient to obtain the difference. Visual difference. This conversion is not a linear conversion, and the direction of conversion may be randomly disturbed. In order to avoid this, a method may be used in which the target color gamut is only pure colors R, G, B, C, M, and Y of the representative hue, and colors of other gradations and colors between hues are interpolated. Or, the target color gamut is composed of a small number of sampling points of gradation colors from Bk to pure color and from pure color to W,
Other colors may be similarly interpolated. The interpolation method includes linear interpolation and spline interpolation.

[0024]

[Equation 1]

Embodiment 3. FIG. 3 is a block diagram showing a color conversion means used in the color conversion method according to the third embodiment of the present invention. In the figure, parts corresponding to those in FIG. 2 are designated by the same reference numerals, and duplicate description thereof will be omitted. In the figure, 31 is a color space conversion means, and the color conversion means 13 of the present embodiment is the minimum color difference calculation means 2 of the second embodiment.
1. In addition to the minimum color difference correspondence color signal calculation means 22, a color space conversion means 31 is provided.

Next, the operation will be described. The color difference equation in the second embodiment is replaced with parameters of hue, lightness, and saturation, and color conversion is performed using this color difference equation. The L * a * b * color space can be calculated using the three attributes of color: hue (H), lightness (V), and saturation (C). The conversion formula is shown in the following formula (2).

[0027]

[Equation 2]

Color space conversion means 31 using the above equation (2)
After the color space is converted by the equation (1), the visual color difference is calculated using the visual coefficient by applying the above equation (1), and the color having the minimum visual color difference and other than 0 is searched. For the searched color,
An image signal for displaying the color on the image display device is calculated. The visual coefficient range in this case is -1.0 ≤ visual coefficient ≤ 1.0
Becomes

As described above, in the present embodiment, the visual coefficient is represented by the parameters of hue, lightness, and saturation, so that the color conversion operation adapted to the visual sense can be facilitated and can be visually performed. A highly effective color conversion can be realized.

Fourth Embodiment The present embodiment shows a method of calculating a visual coefficient according to the present invention. The lightness of the visual coefficient may be expressed as a function of the saturation, the saturation may be expressed as a function of the lightness, or the hue may be expressed as a function of the saturation. For example, when the lightness represented by L * is 50 or more, the lightness may be set to be inversely proportional to the saturation or monotonically decreasing. In order to suppress the phenomenon that the degree of recognition of the hue difference becomes higher as the saturation becomes higher, it may be set to be inversely proportional to the saturation.

As described above, in the present embodiment, the visual coefficient is expressed as a function of each attribute so that the visual system reflects the hue, the saturation, and the brightness which influence each other to be recognized. , Color conversion with high visual effect can be performed.

Fifth Embodiment FIG. 4 is a block diagram showing a configuration for calculating a visual coefficient used in the color conversion method according to the fifth embodiment of the present invention. In the figure, 41
Is a subjective evaluation means, 42 is a statistical processing means, and 43 is a visual coefficient calculation means.

Next, the operation will be described. In the subjective evaluation means 41, in order to calculate a coefficient suitable for vision, a subjective evaluation experiment is performed by at least three subjects, a relationship of visual influences on hue, brightness, and saturation is obtained, and statistically processed. Then, the visual coefficient is calculated.

Here, the method of the subjective evaluation experiment will be described. Prepare an original color patch in which the chromaticity of at least R, G, B pure colors is known. C, M, Y or
Intermediate colors of representative colors, colors between representative hues, and the like may be included. The color patch may be either a reflective type such as a printed matter or a transmissive type such as an image display device, but it is better to be able to present colors uniformly. Color patches suitable for this experiment include, for example:
Munsell color chart set etc. Four or more color patches are prepared for each attribute, with the original color patch as the center and the chromaticity shifted at equal intervals in the hue, saturation, and lightness directions. This is a comparison patch. The original color patch and the comparison patch are arranged side by side around the height of the subject's line of sight, and the subject sits in the center of these patches and at a position several cm apart from these subjects and the subject is placed side by side. Ask them to give a measure of the distance between patches.
The width of the interval scale may be selected from 10 numerical values or 5 numerical values, and a selectable range is set according to the precision pursued by the experiment. An interval scale for chromaticity is obtained by such a subjective evaluation experiment. When four comparison patches are prepared for each attribute, 4 * 3 interval scale data are obtained for any original patch. The subjective evaluation means shown here is an example, and the subjective evaluation means is not limited to this as long as it is a method that subjectively obtains the interval scale.

The statistical processing means 42 processes the interval scale with variations obtained by the subjective evaluation means 41 based on Thurston's statistical processing method, performs verification, and establishes a highly reliable interval scale.

The visual coefficient calculating means 43 is a statistical processing means 4.
From the highly reliable interval scale obtained by 2, the visual coefficient which means the correlation with the parameters of hue, lightness and saturation is obtained. For example, the visual coefficient is the ratio of the width of the range that the interval scale can take in each attribute.

In this way, in this embodiment, since the visual coefficient is calculated by subjective evaluation, color conversion with a high visual effect can be performed.

Sixth Embodiment FIG. 5 is a diagram showing an example of quadratic approximation by the visual coefficient calculation means 43 used in the color conversion method according to the sixth embodiment of the present invention. 5 is a diagram in which the interval scale calculated by the statistical processing means 42 in the fifth embodiment is plotted, and in the fifth embodiment, the first data, that is, the leftmost data or the fifth data in FIG. The difference in the interval scale between the rightmost data and the third data is taken for each attribute, and the ratio is used as the visual coefficient. This may be the reciprocal.

The present embodiment is a method in which the slope coefficient when this plot is approximated by a quadratic equation is calculated and the ratio of these attributes is used as the visual coefficient. FIG. 5 shows an example of the quadratic approximation, but not limited to the quadratic approximation, the ellipse approximation by the principal component analysis is used to obtain the ratio of the major axis and the minor axis, and the ratio between these attributes It may be a coefficient.

Embodiment 7. FIG. 6 is a diagram showing a color gamut compression state in the case where the color conversion means of the color conversion method according to the seventh embodiment of the present invention has a color gamut compression function. In the above-mentioned color conversion means 13, there is an out-of-gamut color that can be reproduced in the target color reproduction range but cannot be reproduced in the image display device, and therefore it is necessary to replace these colors with reproducible colors. In this case, color gamut compression means may be provided. This is a means for color gamut compression using the color difference formula shown in the third embodiment.

The specific processing method will be described.
A color having the smallest visual color difference from the out-of-gamut color to be gamut-compressed is searched from the surface data in the reproduction area of the image display device. The visual color difference is obtained by using the above formula (1) or a combination of the above formulas (1) and (2).
In the color gamut compression using the color difference formula, the direction of compression may be randomly disturbed.To avoid this, only the representative hue is converted, and other gradation colors and colors between hues are interpolated. Good. The interpolation method includes linear interpolation, non-linear interpolation adapted to a γ curve, and linear interpolation including a polygonal point. The above example is an example in the L * a * b * color space, but the space to be applied is not limited to this.

As described above, in the present embodiment, the visual color difference is calculated from the color difference equation to which the visual coefficient is applied, and the out-of-gamut color is converted into the color having the minimum visual color difference, so that there is no visual discomfort. Color conversion is possible.

Embodiment 8. 7 and 8 are block diagrams showing an example of the configuration of an image display device having a color conversion method according to an eighth embodiment of the present invention. In the figure,
71 is an image signal input means, 72 is a target reproduction area setting means,
Reference numeral 73 is a visual coefficient setting means, 74 is a color conversion means, and 75 is an image display means. Further, 81 is a space conversion means, 82
Is a gamut compression means.

Next, the operation will be described. An image signal composed of at least three color data is input to the image signal input means 71. The input image signal is subjected to input image processing as preprocessing by the image signal input means 71 and output. Here, as the input image processing, processing such as gradation correction processing, pixel number conversion and hue correction color conversion according to the characteristics of the input image signal can be considered.

The target color gamut setting means 72 sets a target color gamut that is stored in advance. As the selection method, for example, a target color gamut that is stored in advance by a user action from the user interface is set. If there is no action from the user, the target color gamut set to the initial value is applied. The target color gamut is
At least representative hue, pure color of R, G, B, C, M, Y and white (W),
Includes chromaticity data for black (Bk). Pure color is, for example, RGB
For signals, R (255,0,0), G (0,255,0), B (0,0,255), C (0,
255,255), M (255,0,255), Y (255,255,0).
The data described in the target color gamut is not limited to this, but pure colors from Bk of representative hues R, G, B, C, M, and Y, and high saturation colors to W.
It may also include chromaticity data of gradation colors of several steps toward. The target color gamut is, for example, the standard color space of NTSC or sRGB,
Target color reproduction characteristics of the image display device may be considered.

These color gamuts are described in chromaticity such as L * a * b * color space or RGB color space, XYZ color space, YCbCr, YUV. Alternatively, it may be described in a color space represented by three signals corresponding to a human pancreatic body using a color adaptation model in consideration of the influence of the environment on the visual sense. The optimum color space for color conversion by the color conversion means 74 performed after this is L * a * b *
Since it is a color space, the L * a * b * color space is used as a basic operation, but the other color spaces described above may be used.

When the information of the color gamut to be selected is described in a color space other than the color space of the input image signal, the target color gamut setting means 73 sets L * a as shown in FIG. * b *
Space conversion means 81 for converting to a color space may be included. The space conversion means 81 converts into the L * a * b * color space using the color reproduction characteristics of the target color reproduction range. For example, when converting from the RGB color space, R, G, B pure colors and W, Bk XYZ chromaticity data are used as the color reproduction characteristics of the reproduction range, and XYZ
The color space is converted to the Z color space, and then the XYZ color space is converted to the L * a * b * color space using a known conversion formula.

The visual coefficient setting means 73 sets a visual coefficient suitable for vision so that color conversion corresponding to human vision can be performed when performing color conversion. The visual coefficient stored in advance is selected and set by the user's action from the user interface, or the user directly inputs the value and holds it as a parameter. If there is no action from the user, the visual coefficient set to the initial value is applied. The visual coefficient is composed of a number of coefficients corresponding to the number of axes of the color space in which the color gamut is described, that is, several spatial dimensions. For example, the L * a * b * color space is composed of three different coefficients. Also, each visual coefficient range is 0.0 ≦ k ≦
Set to 1.0. Or have a width comparable to that.

The color conversion means 74 is a target color reproduction area and visual coefficient setting means 73 set by the target color reproduction area setting means 72.
An image signal displayed on the image display device corresponding to a color in the target color reproduction range is calculated based on the visual coefficient set in step 2.
The color conversion unit 74 newly recalculates the target color gamut by using the visual coefficient, calculates the image color signal for reproducing the target color gamut, and the like, which is not described in the target color gamut. Means for interpolating the colors of. When the target color gamut is described in a color space different from that of the image signal, a color space conversion unit that converts the color space in which the target color gamut is described into the color space of the image signal may be provided.

The color conversion means 74 will be specifically described. For example, the visual coefficients may be weighting coefficients L1, a1, b1 for L * a * b *. Data of the target color gamut is multiplied by these coefficients, and the calculation result is set as a new target color gamut. The color of the reproduced image depends on the image color signal input to the image display device and the characteristics of the image display device to be displayed. Therefore, in order to reproduce the target reproduction area, data indicating the characteristics of the image display device is required. At least the R, G, B pure colors of the image display device and the XYZ chromaticity data at W, Bk of the image display device are required for the characteristic data of the image display device.

These data are stored in advance as initial values and these data are arbitrarily used, or the user selects the image display device characteristics stored in advance, or the user interface is displayed. The user is allowed to directly input data of these image display device characteristics by using the image display device characteristics. For example, when the target color gamut is represented by data in the L * a * b * color space, the image display device characteristics are calculated using a known formula that represents the relationship between the L * a * b * color space and the XYZ color space. Based on, the data is converted back to XYZ color space data and converted to an image signal using additive color mixing.
Other colors not described in the target color gamut are calculated by interpolation. The interpolation method includes linear interpolation and spline interpolation.

In the color converting means 74, there are out-of-gamut colors that can be reproduced in the target color reproduction range but cannot be reproduced in the image display device, and therefore it is necessary to replace these colors with reproducible colors. In this case, the color gamut compression means 82 may be provided. This is a means for color gamut compression using the color difference formula shown in the third embodiment.

A specific processing method of the color conversion means 74 will be described. A color having the smallest visual color difference from the out-of-gamut color to be gamut-compressed is searched from the surface data in the reproduction area of the image display device. For the visual color difference, use the above formula (1),
Alternatively, it can be obtained by a combination of the above formulas (1) and (2). In the color gamut compression using the color difference formula, the direction of compression may be randomly disturbed.To avoid this, only the representative hue is converted, and other gradation colors and colors between hues are interpolated. Good. The interpolation method is linear interpolation,
There are non-linear interpolation adapted to the γ curve, linear interpolation including polygonal line points, and the like.

The image display means 75 displays the image signal color-converted by the color conversion means 64 on the image display device. Also,
In some cases, these image signals are displayed by performing image processing such as gradation correction processing and data format conversion processing according to the characteristics of the image display device. Further, as the image display means 75, a liquid crystal panel, a CRT, a DLP, a projector or the like can be considered.

In this way, in the present embodiment, the visual color difference is calculated from the color difference formula to which the visual coefficient is applied, and the out-of-gamut color is converted into the color having the minimum visual color difference, so that there is no visual discomfort. An image evaluation device capable of color conversion can be realized.

[0056]

As described above, according to the present invention, in the color conversion method for converting the color space reproduced by the image signal into the target color space, the first color gamut for determining the target color gamut is determined. Since the method includes a step, a second step of determining a visual coefficient suitable for the visual sense, and a third step of performing color conversion based on the target color gamut and the visual coefficient, color conversion with a high visual effect is achieved. There is an effect that can be realized. In addition, since the color conversion is performed using the color difference formula to which the visual coefficient is applied, there is an effect that the color conversion can be visually performed without a feeling of strangeness.

Further, the color space reproduced by the image signal is converted into a color space having hue, lightness, and saturation as variables, and the converted color space is color-converted by a color difference equation to which the visual coefficient is applied. Therefore, there is an effect that the color conversion operation adapted to the visual sense can be facilitated, and the color conversion having a high visual effect can be realized. Further, since the visual coefficient is represented by a function of a variable other than the above variable, there is an effect that color conversion that is visually effective can be performed. Further, when there is a color that cannot be reproduced in the target color reproduction range, a color outside the target color reproduction range is converted using the color difference equation to which the visual coefficient is applied and replaced with a reproducible color. There is an effect that it is possible to perform color conversion without a feeling of strangeness.

Further, the color conversion method according to the present invention comprises the steps of subjectivity evaluation for obtaining the interval scale obtained from the perceptual characteristics, and the statistical processing for making the interval scale more reliable. Since the step of performing and the step of calculating the visual coefficient that means the visual correlation with respect to the three attributes of color based on the highly reliable interval scale are provided, it is possible to perform color conversion with high visual effect. There is an effect. In addition, since the calculation of the visual coefficient is performed based on the approximation of the interval scale, there is an effect that color conversion that is visually more effective can be performed.

Further, the image display device according to the present invention is
Image input means for inputting an image signal composed of at least three or more color data, target color reproduction area setting means for setting a target color reproduction area, visual coefficient setting means for setting a visual coefficient suitable for vision, and Since the color conversion means for performing color conversion of the image signal from the image input means based on the target color reproduction area and the visual coefficient and the image display means for displaying the color-converted image signal are provided, Therefore, it is possible to realize an image display device capable of color conversion without a feeling of strangeness.

Further, since the target color reproduction area setting means calculates the target color reproduction area based on the characteristics of the target color reproduction area or the characteristics of the image display device, it is possible to perform color conversion without a visually uncomfortable image. There is an effect that it can contribute to the realization of a display device. Further, when the visual coefficient setting means selects the visual coefficient suitable for the visual sense, the visual coefficient suitable for the visual sense is changed according to the preference of the user, so that it is possible to perform color conversion with a higher visual effect. effective. Further, when there is a color that cannot be reproduced in the target color reproduction area, the color conversion means performs color conversion of a color outside the target color reproduction area by using the color difference formula to which the visual coefficient is applied to obtain a reproducible color. Since the color gamut compression means for replacement is provided, there is an effect that color conversion with a higher visual effect becomes possible.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram showing a second embodiment of the present invention.

FIG. 3 is a block diagram showing a third embodiment of the present invention.

FIG. 4 is a block diagram showing a fourth embodiment of the present invention.

FIG. 5 is a diagram for explaining a sixth embodiment of the present invention.

FIG. 6 is a diagram for explaining a seventh embodiment of the present invention.

FIG. 7 is a block diagram showing an eighth embodiment of the present invention.

FIG. 8 is a block diagram showing an eighth embodiment of the present invention.

FIG. 9 is a configuration diagram showing a conventional image display device.

[Explanation of symbols]

11 target color gamut determination means, 12 visual coefficient determination means, 13 color conversion means, 21 minimum color difference calculation means, 22
Minimum color difference correspondence color signal calculation means, 31 color space conversion means, 41 subjective evaluation means, 42 statistical processing means, 43
Visual coefficient calculation means, 71 image signal input means, 72 target reproduction area setting means, 73 visual coefficient setting means, 74 color conversion means, 75 image display means, 81 spatial conversion means, 82 color gamut compression means.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 5B057 CA01 CA08 CA12 CA16 CB01                       CB08 CB12 CB16 CE11 CE17                       CE18                 5C066 AA01 CA08 EE02 GA01 KE03                       KE04 KP05                 5C077 LL19 MP08 PP32 PP33 PP36                       PP37 PP48 PQ12 PQ18 SS06                       TT02 TT09                 5C079 HB01 HB03 HB08 HB12 LB02                       MA11 MA17 MA19 NA03 PA03                       PA05

Claims (11)

[Claims] 1. A color conversion method for converting a color space reproduced by an image signal into a target color space, a first step of determining a target color reproduction range, and a first step of determining a visual coefficient suitable for vision. 2. A color conversion method comprising the step 2 and a third step of performing color conversion based on the target color gamut and the visual coefficient. 2. The color conversion method according to claim 1, wherein the color conversion is performed by using a color difference formula to which the visual coefficient is applied. 3. The color space reproduced by the image signal is converted into a color space having hue, lightness, and saturation as variables, and the converted color space is color-converted by a color difference formula to which the visual coefficient is applied. The color conversion method according to claim 2, wherein 4. The color conversion method according to claim 3, wherein the visual coefficient is represented by a function of a variable other than the variable. 5. When there is a color that cannot be reproduced in the target color reproduction range, color outside the target color reproduction range is converted into a color that can be reproduced by color conversion using a color difference formula to which the visual coefficient is applied. The color conversion method according to claim 3, wherein: 6. A step of subjectivity evaluation for obtaining an interval measure obtained from perceptual characteristics, a step of statistical processing for making the interval measure a more reliable interval measure, and a step of performing the high reliability. Calculating a visual coefficient that means a visual correlation with respect to the three attributes of color based on the interval scale. 7. The color conversion method according to claim 6, wherein the calculation of the visual coefficient is performed based on the approximation of the interval scale. 8. An image input means for inputting an image signal consisting of at least three or more color data, a target color reproduction area setting means for setting a target color reproduction area, and a visual coefficient for setting a visual coefficient suitable for vision. A setting means, a color conversion means for performing color conversion of the image signal from the image input means based on the target color reproduction range and the visual coefficient, and an image display means for displaying the color-converted image signal. An image display device characterized by the above. 9. The image display apparatus according to claim 8, wherein the target color reproduction area setting means calculates the target color reproduction area based on the characteristics of the target color reproduction area or the characteristics of the image display apparatus. 10. The visual coefficient setting means, when selecting a visual coefficient suitable for vision, changes the visual coefficient suitable for vision according to a user's preference. Image display device. 11. If there is a color that cannot be reproduced in the target color reproduction area, the color conversion means performs color conversion of a color outside the target color reproduction area by using a color difference formula to which the visual coefficient is applied, and reproduces the color. The image display device according to any one of claims 8 to 10, further comprising a color gamut compression unit that replaces a color that can be reproduced.