Color reproduction method

• US 6,072,464 A
• Filed: 04/29/1997
• Issued: 06/06/2000
• Est. Priority Date: 04/30/1996
• Status: Expired due to Fees

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Ozeki, Toru
• Primary Examiner(s): Hjerpe, Richard A.
• Assistant Examiner(s): Laneau, Ronald
• Application Number:
  US08/848,165
• Time in Patent Office: 1,134 Days
• Field of Search: 345/154, 345/132, 345/153, 345/199, 348/645, 358/80
• US Class Current: 345/603
• CPC Class Codes: G09G 1/285 Interfacing with colour displays, e.g. TV receiver
• CPC Class Codes: G09G 2320/0606 Manual adjustment
• CPC Class Codes: G09G 2320/0666 for control of colour parameters, e.g. colour temperature
• CPC Class Codes: G09G 5/04 using circuits for interfacing with colour displays
• CPC Class Codes: H04N 1/6016 Conversion to subtractive colour signals

Abstract

The present invention provides color reproduction method to reproduce arbitrary colors at high precision simply without requiring a number of preparatory steps. As a means for conversion between CMYK signal value and arbitrary chromaticity, a color material transfer amount which is a physical amount is handled as intermediate amount. A single color characteristic indicating a relation between the signal value and the color material transfer amount and a color mixing characteristic indicating a relation between each color material transfer amount (ink amount) of a plurality of inks and the chromaticity are obtained. By synthesizing the obtained single color characteristic and color mixing characteristic, the signal value/chromaticity characteristic is obtained in the form of a color conversion table.

Claims

1. A color reproduction method using a color reproduction apparatus which has a plurality of primary colors, converts color information values expressed by a first color space as predetermined colors to device values expressed by a second color space different from said first color space in order to determine formation amounts of respective primary colors for reproducing said color information values by colors by mixing the primary colors on a medium in which the colors are to be reproduced and outputs colors corresponding to said device values to reproduce said predetermined colors on said medium in which the colors are to be reproduced, the formation amounts of respective primary colors being amounts of color materials or light emission amounts which are expressed by the second color space, said method comprising:

obtaining single color characteristic of each of said primary colors which expresses a relation between the formation amount of each primary color for color reproduction by mixing said plurality of the primary colors and the device value for determining said formation amount;

obtaining color mixing characteristic which expresses a relation between a predetermined formation amount of each of said plurality of the primary colors and chromaticity of colors reproduced by formation of the colors depending on said each predetermined formation amount, according to said obtained single color characteristic, said color mixing characteristic being obtained separately from said single color characteristic; and

converting the color information value of each arbitrary color of said first color space to said device value according to the obtained single color characteristic and color mixing characteristic.

2. A color reproduction method according to claim 1 wherein said single color characteristic and said color mixing characteristic are obtained by using a color reproduction apparatus based on subtractive mixture capable of forming arbitrary colors by synthesizing a plurality of primary colors in which subtractive mixture is established.

3. A color reproduction method according to claim 1 wherein said color mixing characteristic estimates the formation amount of each primary color corresponding to arbitrary chromaticity by conducting spline interpolation based on a plurality of relations between the predetermined formation amount of each of said plurality of the primary colors and chromaticity of color reproduced by formation of the color depending on said formation amount.

4. A color reproduction method according to claim 1 wherein when another color material different from a color material for forming said primary colors used for obtaining said single color characteristic and said color mixing characteristic is used, if the another color material is a color material having substantially same color, only said single color characteristic is obtained.

5. A color reproduction method according to claim 4 wherein when the single color characteristic is obtained by using said another color material, the single color characteristic of said another color material is obtained from a relation between the formation amount of said another color material and the device value for determining said formation amount, and when a maximum formation amount in the obtained single color characteristic of the another color material is less than a maximum formation amount in the single color characteristic of other substantially same color material other than said another color material, as a maximum formation amount in the single color characteristic of said other color material, a maximum formation amount of said another color material is set and the maximum formation amount in the single color characteristic of said another color material is made to correspond to a device value corresponding to a formation amount exceeding the maximum formation amount of the another color material to obtain the single color characteristic of each of said primary colors.

6. A color reproduction method according to claim 1 wherein when hue of said predetermined color to be reproduced is adjusted, a single color characteristic corresponding to a hue to be adjusted of said plurality of the single color characteristics is adjusted.

7. A color reproduction method according to claim 1 wherein said formation amount is a variable depending on a color difference between a color formed by the device value for determining a color formed depending on the formation amount or said formation amount and color of said medium in which the colors are to be reproduced.

8. A color reproduction method according to claim 7 wherein said single color characteristic is obtained by using charts, said charts being produced for a plurality of colors having substantially same color difference between the color of said medium and the color produced by the maximum formation amount.

9. A color reproduction method using a color reproduction apparatus based on additive mixture, in which color information values expressed by a first color space as predetermined colors are converted to device values expressed by a second color space different from the first color space and colors corresponding to the device values are output to reproduce the predetermined colors, the color reproduction method comprising:

inputting a device value of single color of a predetermined value for each color of the second color space, measuring respective output colors to obtain measuring values, inputting a plurality of the device values for mixed color in which respective colors of the second color space are preliminarily determined, and measuring respective colors of a plurality of output colors to obtain measuring values, the measuring values obtained by the device value of single color for each color of the second color space and the measuring values obtained by the device values for mixed color are obtained separately;

obtaining a characteristic of conversion between the device value and the intensity information value for each color of the second color space based on a plurality of correspondences between the device value and the intensity information value, such that the plurality of correspondences are included and correspondences between the device value and the intensity information value except said plurality of correspondences are such that, of neighboring correspondences caused when the device values or the intensity information values are arranged from larger to smaller, any device value located between a device value of correspondence on one side, which value is small and a device value of correspondence on the other side, which value is large corresponds to any intensity information value located between an intensity information value of correspondence on one side, which value is small and an intensity information value of correspondence on the other side which value is large; and

converting arbitrary color information value of respective colors of the determined color space to the device value by utilizing the obtained conversion characteristic.

10. A color reproduction method according to claim 9, wherein spline function is determined by a correspondence between the device value and the intensity information value and the conversion characteristic is obtained by using the spline function.

11. A color reproduction method according to claim 9, wherein a plurality of correspondences between the device value and the intensity information value, the plurality of correspondences being preliminarily obtained, utilize correspondences in which intervals between obtained intensity information values are of substantially the same.

12. A color reproduction method using a color reproduction apparatus in which color information values expressed by a first color space as predetermined colors are converted to device values expressed by a second color space different from the first color space and colors corresponding to the device values are output to reproduce the predetermined colors, the color reproduction method comprising:

inputting a plurality of predetermined device values for each color of said second color space, measuring each of a plurality of output colors and obtaining intensity information values of colors to be output from the color reproduction apparatus based on color measuring values;

determining a spline function based on a correspondence between the device value and the intensity information value, with a spline interpolation being carried out so that a slope of a line passing through an interpolated point is the same as a slope of a line connecting measured points before and after the interpolated point;

using the spline function to obtain a conversion characteristic of conversion between the device value and the intensity information value for each color of the second color space based on a plurality of correspondences between the device value and the intensity information value, such that the plurality of correspondences are included and correspondences between the device value and the intensity information value except said plurality of correspondences are such that, of neighboring correspondences caused when the device values or the intensity information values are arranged from larger to smaller, any device value located between a device value of correspondence on one side, which value is small and a device value of correspondence on the other side, which value is large corresponds to any intensity information value located between an intensity information value of correspondence on one side, which value is small and an intensity information value of correspondence on the other side which value is large; and

converting arbitrary color information value of respective colors of the determined color space to the device value by utilizing the obtained conversion characteristic.

13. A color reproduction method according to claim 12, wherein a plurality of correspondences between the device value and the intensity information value, the plurality of correspondences being preliminarily obtained, utilize correspondences in which intervals between obtained intensity information values are of substantially the same.