Method of color conversion, apparatus for the same, and computer program product for realizing the method

• US 6,366,291 B1
• Filed: 07/10/1998
• Issued: 04/02/2002
• Est. Priority Date: 07/17/1997
• Status: Expired due to Term

• Current Assignee: SCREEN Holdings Co., Ltd.
• Original Assignee: SCREEN Holdings Co., Ltd.
• Inventors: Taniguchi, Kazutaka, Sakamoto, Takashi, Narazaki, Makoto
• Primary Examiner(s): Luu, Matthew
• Assistant Examiner(s): HARRISON, CHANTE E
• Application Number:
  US09/113,616
• Time in Patent Office: 1,362 Days
• Field of Search: 345/150, 345/153, 345/154, 345/147, 345/600, 345/604, 345/603, 345/593, 348/34, 348/32, 348/582, 348/659, 358/523, 358/515, 358/518, 358/520
• US Class Current: 345/603
• CPC Class Codes: G09G 1/285 Interfacing with colour displays, e.g. TV receiver

Abstract

A CPU 20 assumes a virtual color monitor in which actual chromaticity coordinates of colors expressed by fluorescent materials are replaced by virtual chromaticity coordinates having the same hues as those of the actual chromaticity coordinates but higher saturations than those of the actual chromaticity coordinates. The CPU 20 converts colorimetric values X, Y, and Z into luminance-linear values r′, g′, and b′ for red, green, and blue, based on a relationship of color conversion for the virtual color monitor at step S23. The CPU 20 then sets any one of the values r′, g′, and b′ to L at step S24 and compares the value L with i at step S26, where i is the γ-th power of j and greater than 0. In case that the value L is less than i, the CPU 20 calculates a value c based on the remaining values other than the value L among the values r′, g′, and b′ at step S27. When −ck≦L<0, conversion of the value L into V is carried out according to a linear function of L, in which an L intercept is varied with a variation of the value c, at step S28. In case that the value L is not less than i, on the other hand, the CPU 20 carries out conversion of the value L into V according to a function of 1/γ-th power of L at step S30. At subsequent step S32, the CPU 20 sets the value V thus obtained to one of display signals R, G, and B corresponding to one of the values r′, g′, and b′ set at step S24. This color conversion process effectively prevents abnormal tone or a change in hue in an area of a desired color that is out of a reproducible color range.

Claims

1. A method of converting colorimetric values representing a composite color into display signals that are to be input into a target color display device to reproduce the composite color, the display signals being related to mixing quantities of device primary colors in a color mixture, the device primary colors being single-color components reproduced by respective single-color elements of the target color display device, the composite color being reproduced by the target color display device as a mixture of the device primary colors mixed in quantities according to the display signals, the target color display device having a reproducible range of the mixing quantity for each of the device primary colors, the method comprising:

(a) defining a definition range of intensities of the display signals which are to be converted in the target color display device to the mixing quantities of the device primary colors within the reproducible range, the definition range being divided into a first conversion range and a second conversion range;

(b) converting the colorimetric values for the composite color into the mixing quantities of the device primary colors according to a first conversion relation; and

(c) converting the mixing quantities of the device primary colors into the intensities of the display signals according to a second conversion relation, comprising;

(i) determining a defined relievable range for at least one selected device primary color among the device primary colors as a function of the mixing quantities of the remaining device primary colors other than the selected device primary color, the relievable range being out of and adjacent to the reproducible range and within a predetermined maximum relievable range;

wherein

(ii) when the mixing quantity of the selected device primary color is within the reproducible range, converting the mixing quantity of the selected device primary color into the intensity of the display signal within the first conversion range; and

(iii) when the mixing quantity of the selected device primary color is within the relievable range, converting the mixing quantity of the selected device primary color into the intensity of the display signal within the second conversion range;

wherein;

the relievable range is determined so that an extent of the relievable range increases as the mixing quantities of the remaining device primary colors increases; and

a ratio of the second conversion range to the definition range is smaller than a ratio of the reproducible range to the maximum relievable range.

2. A method in accordance with claim 1, wherein

the relievable range is determined only when the mixing quantity of the selected device primary color is out of the reproducible range.

3. A method in accordance with claim 1, wherein the step (c) further comprises the steps of:

providing first and second functions usable to represent the second conversion relation, the second function being adjustable by the mixing quantities of the remaining device primary colors;

selecting the first function to represent the second conversion relation when the mixing quantity of the selected device primary color is within the reproducible range; and

selecting the second function to represent the second conversion relation when the mixing quantity of the selected device primary color is within the maximum relievable range.

4. A method in accordance with claim 1, wherein the first conversion relation used in the step (b) represents conversion from the colorimetric values to mixing quantities of virtual device primary colors of a virtual color display device, the virtual color display device having virtual single-color elements reproducing virtual single-color components associated with the single-color components reproduced by the single-color elements of the target color display device, respectively, wherein at least one selected virtual single-color component is determined so that the selected virtual single-color component has an identical hue with that of the associated single-color component and a higher saturation than that of the associated single-color component.

5. A method in accordance with claim 4, wherein

the selected virtual single-color component corresponds to a first chromaticity point in a chromaticity diagram of a uniform color space coordinate system and the associated single-color component corresponds to a second chromaticity point in the chromaticity diagram, the first chromaticity point being determined to be present on a straight line that connects an achromatic color point with the second chromaticity point.

6. A method in accordance with claim 4, wherein

all of the virtual single-color components are determined so that each of the virtual single-color components has an identical hue with that of the associated single-color component and a higher saturation than that of the associated single-color component by a ratio common to all of the virtual single-color components.