Color image correction based on characteristics of a highlights or other predetermined image portion

• US 5,181,105 A
• Filed: 08/02/1991
• Issued: 01/19/1993
• Est. Priority Date: 05/30/1986
• Status: Expired due to Term

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Takiguchi, Hideo, Udagawa, Yoshiro
• Primary Examiner(s): Coles, Sr., Edward L.
• Assistant Examiner(s): VU, KIM Y
• Application Number:
  US07/739,660
• Time in Patent Office: 536 Days
• Field of Search: 358/75, 358/78, 358/80, 358/461, 358/22, 358/41, 358/43, 358/44, 358/29
• US Class Current: 358/520
• CPC Class Codes: H04N 1/6019 using look-up tables H04N1/6025 takes precedence
• CPC Class Codes: H04N 1/608 within the L, C1, C2 colour signals
• CPC Class Codes: H04N 1/628 Memory colours, e.g. skin or sky
• CPC Class Codes: H04N 1/646 Transmitting or storing colour television type signals, e.g. PAL, Lab; Their conversion into additive or subtractive colour signals or vice versa therefor H04N1/642, H04N1/644 take precedence

Abstract

A color image processing apparatus comprises: a circuit to provide a color image signal consisting of a luminance signal and two color difference signals; a converter to convert the two color difference signals into the hue signal and saturation signal; a compressing circuit to independently compress the dynamic ranges of one of or both of the luminance signal and the saturation signal and to output; a memory to store the hue signal and the output of the compressing circuit; and a color printer to reproduce the color image on the basis of the hue signal, saturation signal, and luminance signal stored in the memory. The compressing circuit performs the compression on the basis of a frequency distribution of the input signal levels. With this apparatus, the color balance can be automatically adjusted by use of correction ROMs of a small memory capacity.

Claims

1. A color image processing apparatus comprising:

detecting means for detecting a pixel of a predetermined luminance from a color image signal consisting of a luminance signal and color difference signals;

correction amount operating means for calculating correction amounts to the color difference signals of each of pixels constituting an image from the color difference signals of the pixels of a predetermined luminance; and

correcting means for correcting the color difference signals of each of the pixels constituting the image in accordance with said correction amounts.

2. A color image processing apparatus according to claim 1, wherein said predetermined luminance is the maximum luminance.

3. A color image processing apparatus according to claim 2, wherein said correction amounts are obtained by proportionally distributing the color differences regarding the pixel of the maximum luminance in accordance with a ratio of the luminances of the respective component pixels of the image for said maximum luminance.

4. A color image processing apparatus according to claim 1, wherein said correcting means subtracts said correction amounts from the color differences of each component pixel of the image.

5. A color image processing apparatus comprising:

detecting means for detecting a plurality of pixels of a high saturation from a color image signal consisting of a luminance signal and color difference signals;

operating means for calculating the average value of the color difference signals of said plurality of high luminance pixels; and

correcting means for correcting the color difference signals of each of the pixels constituting the image using said average value as a maximum correction amount.

6. A color image processing apparatus according to claim 5, wherein said plurality of high luminance pixels include the pixel of the maximum luminance.

7. A color image processing apparatus according to claim 6, wherein said correcting means subtracts the amounts derived by proportionally distributing the average value in accordance with the ratio of the luminances of the respective component pixels of the image to the maximum luminance from the color differences of each component pixel of the image.

8. A color image processing apparatus comprising:

means for providing a color image signal consisting of a luminance signal and color difference signals;

detecting means for detecting the color difference signals of a pixel of a high luminance from the color image signal;

a conversion table of correction amounts for correcting the color difference signals of each of the pixels constituting the image of said color image signal; and

correcting means for subtracting the correction amounts from said conversion table from the color difference signals of each component pixel of the image,

wherein the luminance signal and color difference signals of the pixel to be corrected and the color difference signals of one or a plurality of pixels are input to said conversion table.

9. A color image processing apparatus according to claim 8, wherein said detecting means detects one pixel of the maximum luminance.

10. A color image processing apparatus according to claim 8, wherein said detecting means detects a plurality of pixels of a high luminance below the maximum luminance and outputs the average value of the color differences of said plurality of high luminance pixels.

11. A color image processing apparatus according to claim 8, wherein said conversion table is a memory in which the color differences as outputs of said detecting means are previously proportionally distributed in accordance with the ratio of the luminances of the respective component pixels of the image for a predetermined luminance and the resultant color differences are stored.

12. A color image processing method comprising the steps of:

detecting a highlight point in a color image;

detecting a color component of the detected highlight point;

supplying a luminance component of the color image other than that of the highlight point; and

correcting a color component other than that of the highlight point in accordance with the luminance component and the detected color component.

13. A color image processing method according to claim 12, wherein the color component other than the color component of the highlight point is a signal represented by a color difference signal.

14. A color image processing method according to claim 13, further comprising the step of converting the color difference signal into a hue signal and a saturation signal.

15. A color image processing method according to claim 14, further comprising the step of outputting Y, M and C signals on the basis of the hue signal, saturation signal and luminance component.

16. A color image processing method according to claim 15, further comprising the step of supplying the Y, M and C signals to a recording means.

17. A digital color image processing apparatus comprising:

highlight point detecting means for detecting a highlight point in a color image;

highlight point color component detecting means for detecting a color component of the detected highlight point;

luminance signal supplying means for supplying a luminance component of the color image other than that of the highlight point; and

correcting means for correcting a color component other than that of the highlight point in accordance with the luminance component and the detected color component.

18. A color image processing apparatus according to claim 17, wherein the color component other than the color component of the highlight point is a signal represented by a color difference signal.

19. A color image processing apparatus according to claim 18, further comprising converting means for converting the color difference signal to a hue signal and a saturation signal.

20. A color image processing method according to claim 19, further comprising outputting means for outputting Y, M and C signals on the basis of the hue signal, saturation signal and luminance component.

21. A color image processing apparatus according to claim 20, further comprising color signal supplying means for supplying the Y, M and C signals to a recording means.

22. A digital color image forming method comprising the steps of:

detecting a highlight point in a digital color image data;

detecting a color component of the detected highlight point;

correcting a digital color component of the digital color image data in accordance with the detected color component of the detected highlight point; and

forming a printed color image in accordance with the corrected digital color image data.

23. A digital color image forming method according to claim 22, wherein, in said step of detecting a color component of the detected highlight point, an average is taken of the color components for a plurality of pixels of the highlight point.

24. A digital color image forming method according to claim 22, wherein, in said step of forming a printed color image, a printed color image is formed by ink jet recording means.

25. A digital color image forming method according to claim 22, wherein, in said step of forming a printed color image, a printed color image is formed in accordance with Y, M and C signals.