Color correction system for transforming color image from one color space to another

• US 5,436,739 A
• Filed: 12/02/1992
• Issued: 07/25/1995
• Est. Priority Date: 12/03/1991
• Status: Expired due to Term

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Aoki, Shin, Ohuchi, Satoshi, Saitoh, Takashi, Imao, Kaoru
• Primary Examiner(s): Rogers, Scott A.
• Application Number:
  US07/984,646
• Time in Patent Office: 965 Days
• Field of Search: 358/518, 358/519, 358/520, 358/521, 358/523, 358/525, 395/109, 345/153, 345/154
• US Class Current: 358/518
• CPC Class Codes: H04N 1/6016 Conversion to subtractive colour signals

Abstract

A color correction apparatus includes a preprocessor for generating a minimum value signal, a set of difference signals, and a selecting signal in accordance with values of input XYZ color data, the minimum value signal indicating a minimum value among the input XYZ color values, the difference signals indicating differences between the minimum value and the remaining values of the input XYZ color data, and the selecting signal being used to select one of unit triangular prisms in XYZ color space, a first part for computing a first signal of output color data through interpolation being performed, using predetermined values of output colors corresponding to lattice points of the selected unit triangular prism, in accordance with a value of the minimum value signal and in accordance with values of the difference signals, a second part for computing a second signal of the output color data in accordance with the value of the minimum value signal, and a third part for generating a third signal indicating the output color data by adding the first signal and the second signal.

Claims

1. A color correction apparatus for transforming input XYZ color data into output color data, said color correction apparatus comprising:

a) preprocessing means for generating a minimum value signal, a set of difference signals, and a selecting signal in accordance with values of the input XYZ color data, wherein;

1) said minimum value signal indicates a minimum value among the input XYZ color data values,

2) said difference signals indicate differences between the minimum value and the remaining values of the input XYZ color data, and

3) said selecting signal is used to select one of unit triangular prisms in XYZ color space;

b) first means for generating a first signal of output color data through interpolation which is performed, using predetermined values of output colors corresponding to lattice points of the unit triangular prism selected by said selecting signal, in accordance with a value of said minimum value signal and in accordance with values of said difference signals;

c) second means for generating a second signal of the output color data in accordance with the value of the minimum value signal; and

d) third means for generating a third signal indicating a sum of the output color data resulting after said first signal from said first means and said second signal from said second means are added, wherein said third means includes;

d1) limiting means for performing a limiting process for said third signal, wherein;

i) the sum of the output color data is set to a predetermined highest color value when the sum of the output color data indicated by the third signal is higher than the predetermined highest color value; and

ii) the sum of the output color data is set to a predetermined lowest color value when the sum of the output color data indicated by the third signal is lower than the predetermined lowest color value.

2. A color correction apparatus according to claim 1, wherein:

said first means includes a parameter memory for storing a plurality of predetermined parameters at predetermined address of said parameter memory;

said first means reads out one of the sets of the predetermined parameters from said parameter memory at an address of said parameter memory indicated by said selecting signal, so that said first signal is generated using the set of the predetermined parameters read out from the parameter memory.

3. A color correction apparatus according to claim 1, wherein said third means includes:

an adder for computing a sum of the first signal generated by the first means and the second signal generated by the second means in order to generate a third signal indicating the sum of the output color data.

4. A color correction apparatus according to claim 1, wherein:

said minimum value signal is a signal indicating an achromatic component of the input XYZ color data; and

said difference signals are signals respectively indicating a first color component and a second color component of the input XYZ color data.

5. A color correction apparatus for transforming input XYZ color data into output color data, said color correction apparatus comprising:

a) minimum signal generating means for generating a minimum value signal in accordance with a minimum value among values of input XYZ color data;

b) difference signal generating means for generating difference signals indicating differences between said minimum value and the remaining values of the input XYZ color data;

c) selecting means, responsive to said difference signals, for selecting one of triangular areas in a two-dimensional color space in which the values of the input XYZ color data are described;

d) first means for generating a first signal of output color data through interpolation which is performed, using predetermined values of output colors corresponding to lattice points of said selected triangular area, in accordance with a value of said minimum value signal and in accordance with values of said difference signals;

e) second means for generating a second signal of the output color data in accordance with the value of the minimum value signal; and

f) third means for generating a third signal indicating a sum of the output color data resulting after the first signal from the first means and the second signal from the second means are added, wherein said third means includes;

f1) limiting means for performing a limiting process for said third signal, wherein;

i) the sum of the output color data is set to a predetermined highest color value when the sum of the output color data indicated by the third signal is higher than the predetermined highest color value; and

ii) the sum of the output color data is set to a predetermined lowest color value when the sum of the output color data indicated by the third signal is lower than the predetermined lowest color value.

6. A color correction apparatus according to claim 5, wherein said first mean includes:

two multipliers for computing, through said interpolation, the first signal of the output color data in accordance with the value of the minimum value signal and in accordance with the values of the difference signals.

7. A color correction apparatus according to claim 5, wherein:

the values of output colors corresponding to lattice points of each of the triangular areas in the two-dimensional color space are predetermined such that the values are continuous at boundaries between the triangular areas.

8. A color correction apparatus according to claim 5, wherein:

said minimum value signal is a signal indicating an achromatic component of the input XYZ color data; and

said difference signals are signals indicating two color components of the input XYZ color data.

9. A color correction apparatus according to claim 5, wherein:

said second means generates the second signal of the output color data in accordance with the minimum value signal and generates a fourth signal of correction data in accordance with a sum of a predetermined combination of products of the minimum value signal and the difference signals, and

said third means generates said third signal by adding said first signal, said second signal and said fourth signal.