Method and apparatus for compensating for color in color images

• US 5,467,438 A
• Filed: 05/24/1993
• Issued: 11/14/1995
• Est. Priority Date: 10/13/1989
• Status: Expired due to Fees

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Nishio, Kazutaka, Naka, Toshiya, Nishimura, Kenji, Nakase, Yoshimori
• Primary Examiner(s): Herndon, Heather R.
• Assistant Examiner(s): SMITH, MICHAEL
• Application Number:
  US08/065,427
• Time in Patent Office: 904 Days
• Field of Search: 395/131, 395/132, 395/126, 358/75, 358/80, 358/703, 364/525
• US Class Current: 345/600
• CPC Class Codes: G06T 15/506 Illumination models

Abstract

Color compensation is performed in color images for use in an image processing field which is employed for three-dimensional computer graphics and the like by making a luminance value of texture data coincide with an intensity derived by an intensity calculation. Also, lightness compensation is performed for a color image according to a display scene. From measurements of color changes of plural colors in a uniform color space, a color change of arbitrary texture data under a chromatic color light source is represented and compensated. The generated image is very natural because compensation is achieved between a lightness of a texture itself representing a pattern on the surface of an object and an intensity of the surface of the object derived by an intensity calculation when an image is generated.

Claims

1. A color compensation method for a three-dimensional color image, said method comprising the steps of:

obtaining mapping data, in a uniform color space, representative of a transformation from chromaticity coordinate values of a standard white patch and a standard color patch irradiated with an achromatic reference light to respective chromaticity coordinate values of said standard white patch and said standard color patch irradiated with a chromatic color reference light;

irradiating an object surface with said achromatic reference light; and

determining a chromaticity coordinate value of said object surface irradiated with said chromatic reference light based on (i) said mapping data and (ii) a coordinate value of said object surface irradiated with said achromatic reference light.

2. A color compensation device for three-dimensional color image generation, said device comprising a color space mapping unit, said color mapping unit comprising:

means for obtaining mapping data, in a uniform color space, representative of a transformation from chromaticity coordinate values of a standard white patch and a standard color patch irradiated with achromatic reference light to respective chromaticity coordinate values of said standard white patch and said standard color patch irradiated with a chromatic reference light,

means for irradiating an object surface with said achromatic reference light; and

means for determining a chromaticity coordinate value of said object surface irradiated with said chromatic reference light based on (i) said mapping data and (ii) a coordinate value of said object surface irradiated with said achromatic reference light.

3. A color compensation method for a three-dimensional image, said method comprising the steps of:

providing a standard white patch;

irradiating said standard white patch with a chromatic color reference light, determining the lightness level of said standard white patch, and setting said determined lightness level as a reference lightness level;

determining, when changing lightness of color image data, a changing ratio of saturation based on lightness of said color image data before and after changing said lightness of said color image data; and

simultaneously changing (i) the lightness of said color image data in a uniform color space and (ii) a color saturation degree of the color image data in accordance with said changing ratio, such that a change of the lightness level of said color image data does not exceed said reference lightness level.

4. A color compensation device for three-dimensional color image generation, said device including a color compensation unit comprising:

means for irradiating a standard white patch with a chromatic color reference light, and determining the lightness level of said standard white patch, and setting said determined lightness level as a reference lightness level;

means for determining, when changing lightness of color image data, a changing ratio of saturation based on lightness of the color image data before and after changing said lightness of said color image data; and

means for simultaneously changing (i) said lightness of said color image data in a uniform color space and (ii) a color saturation degree of said color image data in accordance with said changing ratio, such that a change of the lightness level of said color image data does not exceed said reference lightness level.

5. A color compensation method for a three-dimensional color image, said method comprising the steps of:

(a) providing a standard white patch;

(b) irradiating said standard white patch with an achromatic reference light;

(c) determining a first chromaticity coordinate value for said standard white patch indicative of a chromaticity of said standard white patch while being irradiated with said achromatic reference light;

(d) providing a standard color patch;

(e) irradiating said standard color patch with said achromatic reference light;

(f) determining a first chromaticity coordinate value for said standard color patch indicative of a chromaticity of said standard color patch while being irradiated with said achromatic reference light;

(g) irradiating said standard white patch with a chromatic reference light;

(h) determining a second chromaticity coordinate value for said standard white path indicative of a chromaticity of said standard white patch while being irradiated with said chromatic reference light;

(i) irradiating said standard color patch with said chromatic reference light;

(j) determining a second chromaticity coordinate value for said standard color patch indicative of a chromaticity of said standard color patch while being irradiated with said chromatic reference light;

(k) obtaining mapping data, in a uniform color space, representative of a transformation from (1) said first chromaticity coordinate values of said standard white patch and said standard color patch to (2) said second chromaticity coordinate values of said standard white patch and said standard color patch;

(l) providing an object surface;

(m) irradiating said object surface with said achromatic reference light;

(n) determining a first chromaticity coordinate value for said object surface indicative of a chromaticity of said object surface while being irradiated with said achromatic reference light; and

(o) determining a second chromaticity coordinate value for said object surface indicative of a chromaticity of said object surface which would result when said object surface is irradiated with said chromatic reference light in accordance with (1) said mapping data and (2) said first chromaticity coordinate value for said object surface.

6. A color compensation device for three-dimensional color image generation, said device comprising a color space mapping unit, said color space mapping unit comprising:

(a) means for irradiating a standard white patch with an achromatic reference light;

(b) means for determining a first chromaticity coordinate value for said standard white patch indicative of a chromaticity of said standard white patch while being irradiated with said achromatic reference light;

(c) means for irradiating a standard color patch with said achromatic reference light;

(d) means for determining a first chromaticity coordinate value for said standard color patch indicative of a chromaticity of said standard color patch while being irradiated with said achromatic reference light;

(e) means for irradiating said standard white patch with a chromatic reference light;

(f) means for determining a second chromaticity coordinate value for said standard white patch indicative of a chromaticity of said standard white patch while being irradiated with said chromatic reference light;

(g) means for irradiating said standard color patch with said chromatic reference light;

(h) means for determining a second chromaticity coordinate value for said standard color patch indicative of a chromaticity of said standard color patch while being irradiated with said chromatic reference light;

(i) means for obtaining mapping data, in a uniform color space, representative of a transformation from (1) said first chromaticity coordinate values of said standard white patch and said standard color patch to (2) said second chromaticity coordinate values of said standard white patch and said standard color patch;

(j) means for irradiating said object surface with said achromatic reference light;

(k) means for determining a first chromaticity coordinate value for said object surface indicative of a chromaticity of said object surface while being irradiated with said achromatic reference light; and

(l) means for determining a second chromaticity coordinate value for said object surface indicative of a chromaticity of said object surface which would result when said object surface is irradiated with said chromatic reference light in accordance with (1) said mapping data and (2) said first chromaticity coordinate value for said object surface.