Method and apparatus for detecting flesh tones in an image

• US 5,638,136 A
• Filed: 06/07/1995
• Issued: 06/10/1997
• Est. Priority Date: 01/13/1992
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Yamada, Takeshi, Kuno, Tetsuya, Kojima, Kazuaki, Sugiura, Hiroaki
• Primary Examiner(s): Peng, John K.
• Assistant Examiner(s): Miller, John W.
• Application Number:
  US08/478,594
• Time in Patent Office: 734 Days
• Field of Search: 348/652, 348/653, 348/649, 348/650, 348/645, 348/651, 358/27, 358/28
• US Class Current: 348/653
• CPC Class Codes: H04N 23/71 Circuitry for evaluating the brightness variation
• CPC Class Codes: H04N 5/2621 Cameras specially adapted for the electronic generation of special effects during image pickup, e.g. digital cameras, camcorders, video cameras having integrated special effects capability
• CPC Class Codes: H04N 9/643 Hue control means, e.g. flesh tone control
• CPC Class Codes: H04N 9/646 for image enhancement, e.g. vertical detail restoration, cross-colour elimination, contour correction, chrominance trapping filters

Abstract

A method and apparatus for adjusting a color difference signal of an image includes a video signal processor. The video signal processor receives a luminance signal and color difference signals representing the image, and accesses a color saturation level from a color saturation level table stored in memory based on the color difference signals. The video signal processor then detects flesh tone in areas of the image based on the luminance signal and the color saturation level, and generates a flesh tone detecting signal based on results of the flesh tone detection.

Claims

1. A method of adjusting a color difference signal of an image in a video signal processor comprising the steps of:

(a) receiving a luminance signal and color difference signals;

(b) determining a color saturation level based on the color difference signals;

(c) comparing the color saturation level and the luminance signal to generate a flesh tone detecting signal indicative of flesh tone or non-flesh tone in an area of an image.

2. A video signal processor, comprising:

a flesh tone detector receiving a luminance signal and color difference signals representing an image, and detecting flesh tone in areas of the image based on the luminance signal and the color difference signals, the flesh tone detector including,

determining means for determining a color saturation level based on the color difference signals; and

a comparing means for comparing the color saturation level with the luminance signal to generate a flesh tone detecting signal indicative of flesh tone or non-flesh tone in an area of an image.

3. A method of adjusting a color difference signal of an image in a video signal processor comprising the steps of:

(a) receiving a luminance signal and color difference signals representing the image;

(b) accessing a color saturation level from a color saturation level table stored in memory based on the color difference signals;

(c) detecting flesh tone in areas of the image based on the luminance signal and the color saturation level; and

(d) generating a flesh tone detecting signal based on results of the step (c).

4. The method of claim 3, wherein

the step (c) compares the color saturation level and the luminance signal;

and

the step (d) generates a flesh tone detecting signal indicative of flesh tone or non-flesh tone in an area of the image based upon the comparison in step (c).

5. The method of claim 4, wherein the step (d) generates the flesh tone detecting signal indicative of flesh tone if the color saturation level is within a predetermined range of the luminance signal.

6. The method of claim 5, wherein the predetermined range is a range encompassing fractional percentages of the luminance signal.

7. The method of claim 3, further comprising the step of:

(e) controlling a gain of at least one of the luminance signal, an aperture correction signal, and the color difference signals based on the flesh tone detecting signal.

8. The method of claim 7, wherein the color difference signals include an R-Y color difference signal and a B-Y color difference signal and step (e) includes the substeps of:

(i) raising the gain of the R-Y color difference signal; and

(ii) lowering the gain of the B-Y color difference signal, if the flesh tone detecting signal is indicative of a detected flesh tone area in the image.

9. The method of claim 8, wherein the color difference signals include an R-Y color difference signal and a B-Y color difference signal, and wherein the method further comprises the steps of:

(g) raising a gain of the R-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image; and

(h) lowering a gain of the B-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

10. The method of claim 8, further comprising the steps of:

(f) generating a processed R-Y color difference signal by subtracting the B-Y color difference signal from the R-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image; and

(g) generating a processed B-Y color difference signal by adding the R-Y color difference signal to the B-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

11. The method of claim 7, further comprising the steps of:

(e) extracting only low frequency components from the flesh tone detecting signal; and

(f) slicing the extracted low frequency components by a predetermined slice level and outputting a resultant signal as the flesh tone detecting signal.

12. The method of claim 11, wherein the step (f) includes the steps of:

(i) slicing the extracted low frequency components by the predetermined level;

(ii) comparing the predetermined level to the extracted low frequency components; and

(iii) outputting as the flesh tone detecting signal one of output from the step (f)(i) and a predetermined constant based on output of the step (f)(ii).

13. The method of claim 11, further comprising the step of (g) raising a gain of the luminance signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

14. The method of claim 11, further comprising the step of (g) lowering a gain of an aperture correction signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

15. The method of claim 11, wherein the color difference signals include an R-Y color difference signal and a B-Y color difference signal, and further comprising the steps of:

(g) controlling a gain of the R-Y color difference signal and a gain of the B-Y color difference signal;

(h) generating a processed R-Y color difference signal by subtracting the B-Y color difference signal from the R-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image; and

(i) generating a processed B-Y color difference signal by adding the R-Y color difference signal to the B-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

16. The method of claim 7, wherein the step (e) includes the substep of (i) raising a gain of the luminance signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

17. The method of claim 7, wherein the step (e) includes the substep of (i) lowering a gain of the aperture correction signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

18. The method of claim 7, wherein

the color difference signals include an R-Y color difference signal and a B-Y color difference signal;

the step (e) controls a gain of the R-Y color difference signal and a gain of the B-Y color difference signal; and

further comprising the steps of,

(f) generating a processed R-Y color difference signal by subtracting the B-Y color difference signal from the R-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image; and

(g) generating a processed B-Y color difference signal by adding the R-Y color difference signal to the B-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

19. The method of claim 3, further comprising the steps of:

(e) extracting low frequency components from the flesh tone detecting signal;

(f) processing output of the step (e) such that increases and decreases in the output of the step (e) increase and decrease in a stepwise manner; and

(g) outputting output of the step (f) as the flesh tone detecting signal.

20. The method of claim 19, wherein the color difference signals include an R-Y color difference signal and a B-Y color difference signal, and wherein the method further comprises the steps of:

(h) raising a gain of the R-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image; and

(i) lowering a gain of the B-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

21. The method of claim 19, further comprising the step of (h) raising a gain of the luminance signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

22. The method of claim 19, further comprising the step of (h) lowering a gain of the aperture correction signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

23. The method of claim 19, wherein the color difference signals include an R-Y color difference signal and a B-Y color difference signal, and further comprising the steps of:

(h) controlling a gain of the R-Y color difference signal and a gain of the B-Y color difference signal;

(i) generating a processed R-Y color difference signal by subtracting the B-Y color difference signal from the R-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image; and

(j) generating a processed B-Y color difference signal by adding the R-Y color difference signal to the B-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

24. The method of claim 3, further comprising the steps of:

(e) extracting low frequency components from the luminance signal;

(f) mixing the luminance signal and output of the step (c) based on the flesh tone detecting signal to generate a processed luminance signal.

25. The method of claim 3, wherein the step (f) increases a proportion of the output of step (e) in the processed luminance signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

26. A video signal processor, comprising:

a flesh tone detector receiving a luminance signal and color difference signals representing an image, and detecting flesh tone in areas of the image based on the luminance signal and the color difference signals, the flesh tone detector including,

a memory storing a color saturation level table, and accessing and outputting a color saturation level from the color saturation level table based on the color difference signals; and

a detecting means for detecting flesh tone in areas of the image based on the luminance signal and the color saturation level, and generating a flesh tone detecting signal based on results of the detecting.

27. The video signal processor of claim 26, wherein the detecting means compares the color saturation level to the luminance signal, and generates the flesh tone detecting signal based upon a result of the comparison.

28. The video signal processor of claim 26, wherein the detecting means outputs the flesh tone detecting signal indicating detection of a flesh tone area in the image when the color saturation level is within a predetermined range of the luminance signal.

29. The video signal processor of claim 28, wherein the predetermined range is a range encompassing fractional percentages of the luminance signal.

30. The video signal processor of claim 26, further comprising:

gain control means for controlling a gain of at least one of the luminance signal, an aperture correction signal, and the color difference signals based on the flesh tone detecting signal.

31. The video signal processor of claim 30, wherein

the color difference signals include an R-Y color difference signal and a B-Y color difference signal;

the gain control means comprises,

a first gain controller raising a gain of the R-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image, and

a second gain controller lowering a gain of the B-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

32. The video signal processor of claim 31, further comprising:

a first operation circuit generating a processed R-Y color difference signal by subtracting the B-Y color difference signal from the R-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image; and

a second operation circuit generating a processed B-Y color difference signal by adding the R-Y color difference signal to the B-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

33. The video signal processor of claim 30, wherein the gain control means raises a gain of the luminance signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

34. The video signal processor of claim 30, wherein the gain control means lowers a gain of the aperture correction signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

35. The video signal processor of claim of claim 30, wherein

the color difference signals include an R-Y color difference signal and a B-Y color difference signal;

the gain control means controls a gain of the R-Y color difference signal and a gain of the B-Y color difference signal;

and further comprising,

a first operation circuit generating a processed R-Y color difference signal by subtracting the B-Y color difference signal from the R-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image; and

a second operation circuit generating a processed B-Y color difference signal by adding the R-Y color difference signal to the B-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

36. The video signal processor of claim 26, further comprising:

a low pass filter extracting low frequency components of the flesh tone detecting signal; and

slicing means for slicing the extracted low frequency components by a predetermined slice level and outputting a resultant signal as the flesh tone detecting signal.

37. The video signal processor of claim 36, wherein the slicing means (i) slices the extracted low frequency components by the predetermined level, (ii) compares the predetermined level to the extracted low frequency components, and (iii) outputs as the flesh tone detecting signal one of output from the slicing and a predetermined constant based on a result of the comparing.

38. The video signal processor of claim 36, wherein

the color difference signals include an R-Y color difference signal and a B-Y color difference signal;

and further comprising,

a first gain controller raising a gain of the R-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image; and

a second gain controller lowering a gain of the B-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

39. The video signal processor of claim 36, further comprising a gain controller raising a gain of the luminance signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

40. The video signal processor of claim 36, further comprising a gain controller lowering a gain of the aperture correction signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

41. The video signal processor of claim of claim 36, wherein

the color difference signals include an R-Y color difference signal and a B-Y color difference signal;

and further comprising,

gain control means for controlling a gain of the R-Y color difference signal and a gain of the B-Y color difference signal;

a first operation circuit generating a processed R-Y color difference signal by subtracting the B-Y color difference signal from the R-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image; and

a second operation circuit generating a processed B-Y color difference signal by adding the R-Y color difference signal to the B-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

42. The video signal processor of claim 26, further comprising:

a low pass filter extracting low frequency components from the flesh tone detecting signal;

a processor processing output of the extracted low frequency components such that increases and decreases in the extracted low frequency components increase and decrease in a stepwise manner, and outputting results of the processing as the flesh tone detecting signal.

43. The video signal processor of claim 42, wherein

the color difference signals include an R-Y color difference signal and a B-Y color difference signal;

and further comprising,

a first gain controller raising a gain of the R-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image; and

a second gain controller lowering a gain of the B-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

44. The video signal processor of claim 42, further comprising a gain controller raising a gain of the luminance signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

45. The video signal processor of claim 42, further comprising a gain controller lowering a gain of the aperture correction signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

46. The video signal processor of claim 42, wherein the mixer increases a proportion of the extracted low frequency components in the processed luminance signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

47. The video signal processor of claim of claim 42, wherein

the color difference signals include an R-Y color difference signal and a B-Y color difference signal;

and further comprising,

gain control means for controlling a gain of the R-Y color difference signal and a gain of the B-Y color difference signal;

a first operation circuit generating a processed R-Y color difference signal by subtracting the B-Y color difference signal from the R-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image; and

a second operation circuit generating a processed B-Y color difference signal by adding the R-Y color difference signal to the B-Y color difference signal if the flesh tone detecting signal indicates detection of a flesh tone area in the image.

48. The video signal processor of claim 26, further comprising:

a low pass filter extracting low frequency components from the luminance signal;

a mixer mixing the luminance signal and the extracted low frequency components in a proportion based on the flesh tone detecting signal to generate a processed luminance signal.