Level compression of a video signal without affecting hue of a picture represented by the video signal

• US 6,111,607 A
• Filed: 04/10/1997
• Issued: 08/29/2000
• Est. Priority Date: 04/12/1996
• Status: Expired due to Term

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Kameyama, Takashi
• Primary Examiner(s): Garber, Wendy
• Assistant Examiner(s): White, Mitchell
• Application Number:
  US08/831,686
• Time in Patent Office: 1,237 Days
• Field of Search: 348/222, 348/223, 348/242, 348/255, 348/254, 348/256, 348/599, 348/672, 348/673, 348/674, 348/675, 348/679, 348/703, 348/712, 348/713, 348/225, 348/645, 348/649, 348/650 , 348/651, 348/652, 348/653, 348/654, 348/655
• US Class Current: 348/256
• CPC Class Codes: G06T 2207/10016 Video; Image sequence
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06T 5/92 based on global image properties
• CPC Class Codes: H04N 9/646 for image enhancement, e.g. vertical detail restoration, cross-colour elimination, contour correction, chrominance trapping filters

Abstract

A level compression and/or gradation conversion of a video signal are performed without causing any change in the hue of a picture represented by that video signal. The knee compression and/or gradation conversion are carried out by multiplying red, green and blue primary color signals by a luminance gain, while the hue and saturation remain unaffected. If the level of any of the primary color signals still exceeds a predetermined threshold level, the saturation conversion is executed by using the saturation gain and the luminance component supplied from a controller. In the saturation conversion operation, the maximum level of at least one of the red, green and blue primary color signals is made coincident with the predetermined threshold level while the hue and luminance of the picture represented by the video signal are maintained unchanged.

Claims

1. A video camera for generating a video signal formed of luminance and chrominance components, said chrominance component defined by hue and saturation components, said video camera comprising:

generator means for generating input three primary color signals having respective levels and representing the video signal;

luminance converter means for generating, as a first stage of a knee compression operation, compressed three primary color signals by compressing the respective levels of the input three primary color signals using one compression rate without affecting the hue and saturation components; and

saturation converter means for adjusting, as a second stage of said knee compression operation, a maximum level detected from the compressed three primary color signals when the detected maximum level exceeds a first predetermined threshold level, wherein the detected maximum level is adjusted to substantially coincide with the first predetermined threshold level without affecting the hue component and the luminance component.

2. The apparatus according to claim 1, wherein the three respective levels are compressed when the luminance component exceeds a second predetermined threshold level.

3. The apparatus according to claim 2, wherein said first predetermined threshold level is selected to be higher than said second predetermined threshold level.

4. The apparatus according to claim 1, wherein said first predetermined threshold level is selected to be higher than a maximum signal level established in accordance with a color television standard.

5. The apparatus according to claim 1, further comprising gamma correction means for performing gamma correction on the compressed three primary color signals following the compression and adjustment by said luminance converter means and saturation converter means, respectively.

6. The apparatus according to claim 5, further comprising matrix means for generating the luminance component and color difference signals based on the compressed three primary color signals that have been processed by said gamma correction means.

7. The apparatus according to claim 1, further comprising input luminance level detector means for detecting the luminance level of the video signal represented by the input three primary color signals;

and compression rate detector means for detecting the compression rate from the detected luminance level.

8. The apparatus according to claim 7, further comprising compressed luminance level detector means for detecting the luminance level of the video signal represented by the compressed three primary color signals;

and level control value detector means for determining, based on the detected compressed luminance level, a level control value such that the maximum level of the compressed three primary color signals is adjusted by said saturation converter means to substantially coincide with the first predetermined threshold level, said saturation converter means adjusting the respective levels of the remaining compressed primary color signals as a function of the level control value.

9. The apparatus according to claim 1, further comprising compressed luminance level detector means for detecting the luminance level of the video signal represented by the compressed three primary color signals;

and level control value detector means for determining, based on the detected compressed luminance level, a level control value such that the maximum level of the compressed three primary color signals is adjusted by said saturation converter means to substantially coincide with the first predetermined threshold level, said saturation converter means adjusting the respective levels of the remaining compressed primary color signals as a function of the level control value.

10. The apparatus according to claim 1, further comprising saturation conversion rate detector means for detecting a saturation conversion rate used in adjusting the saturation component of the video signal represented by the compressed three primary color signals such that the maximum level of at least one compressed primary color signal substantially coincides with the first predetermined threshold level, said saturation converter means adjusting the respective levels of the remaining compressed primary color signals using the detected saturation conversion rate.

11. The apparatus according to claim 1, further comprising saturation conversion rate detector means for detecting the saturation conversion rate used in adjusting the saturation component of the video signal represented by the compressed three primary color signals such that the maximum level of at least one compressed primary color signal substantially coincides with the first predetermined threshold level;

and saturation conversion rate input means for supplying a user selectable saturation conversion rate;

wherein said saturation converter means adjusts the respective levels of the compressed three primary color signals using the lowest rate selected from the detected saturation conversion rate or the user selectable saturation conversion rate.

12. A video signal processor for processing a video signal formed of luminance and chrominance components, said chrominance component defined by hue and saturation components, said video signal processor comprising:

generator means for generating input three primary color signals having respective levels and representing the video signal;

luminance converter means for generating, as a first stage of a knee compression operation, compressed three primary color signals by compressing the respective levels of the input three primary color signals using one compression rate without affecting the hue and saturation components; and

saturation converter means for adjusting, as a second stage of said knee compression operation, a maximum level detected from the compressed three primary color signals when the detected maximum level exceeds a first predetermined threshold level, wherein the detected maximum level is adjusted to substantially coincide with the first predetermined threshold level without affecting the hue component and the luminance component.

13. The apparatus according to claim 12, wherein the three respective levels are compressed when the luminance component exceeds a second predetermined threshold level.

14. The apparatus according to claim 13, wherein said first predetermined threshold level is selected to be higher than said second predetermined threshold level.

15. The apparatus according to claim 12, wherein said first predetermined threshold level is selected to be higher than a maximum signal level established in accordance with a color television standard.

16. The apparatus according to claim 12, further comprising gamma correction means for performing gamma correction on the compressed three primary color signals following the compression and adjustment by said luminance converter means and saturation converter means, respectively.

17. The apparatus according to claim 16, further comprising matrix means for generating the luminance component and color difference signals from the compressed three primary color signals that have been processed by said gamma correction means.

18. The apparatus according to claim 12, further comprising input luminance level detector means for detecting the luminance level of the video signal represented by the input three primary color signals;

and compression rate detector means for detecting the compression rate from the detected luminance level.

19. The apparatus according to claim 18, further comprising compressed luminance level detector means for detecting the luminance level of the video signal represented by the compressed three primary color signals;

and level control value detector means for determining, based on the detected compressed luminance level, a level control value such that the maximum level of the compressed three primary color signals is adjusted by said saturation converter means to substantially coincide with the first predetermined threshold level, said saturation converter means adjusting the respective levels of the remaining compressed primary color signals as a function of the level control value.

20. The apparatus according to claim 12, further comprising compressed luminance level detector means for detecting the luminance level of the video signal represented by the compressed three primary color signals;

and level control value detector means for determining, based on the detected compressed luminance level, a level control value such that the maximum level of the compressed three primary color signals is adjusted by said saturation converter means to substantially coincide with the first predetermined threshold level, said saturation converter means adjusting the respective levels of the remaining compressed primary color signals as a function of the level control value.

21. The apparatus according to claim 12, further comprising saturation conversion rate detector means for detecting a saturation conversion rate used in adjusting the saturation component of the video signal represented by the compressed three primary color signals such that the maximum level of at least one compressed primary color signal substantially coincides with the first predetermined threshold level, said saturation converter means adjusting the respective levels of the remaining compressed primary color signals using the detected saturation conversion rate.

22. The apparatus according to claim 12, further comprising saturation conversion rate detector means for detecting the saturation conversion rate used in adjusting the saturation component of the video signal represented by the compressed three primary color signals such that the maximum level of at least one compressed primary color signal substantially coincides with the first predetermined threshold level;

and saturation conversion rate input means for supplying a user selectable saturation conversion rate;

wherein said saturation converter means adjusts the respective levels of the compressed three primary color signals using the lowest rate selected from the detected saturation conversion rate or the user selectable saturation conversion rate.

23. A video camera for generating a video signal formed of luminance and chrominance components, said chrominance component defined by hue and saturation components, said video camera comprising:

generator means for generating input three primary color signals having respective levels and representing the video signal;

luminance converter means for generating gradation converted three primary color signals by gradation converting the respective levels of the input three primary color signals using one gradation conversion rate without affecting the hue and saturation components; and

saturation converter means for adjusting, as part of a knee compression operation, a maximum level detected from the gradation converted three primary color signals when the detected maximum level exceeds a first predetermined threshold level, wherein the detected maximum level is adjusted to substantially coincide with the first predetermined threshold level without affecting the hue component and the luminance component.

24. The apparatus according to claim 23, wherein the three respective levels are gradation converted when the luminance component exceeds a second predetermined threshold level.

25. The apparatus according to claim 24, wherein said first predetermined threshold level is selected to be higher than said second predetermined threshold level.

26. The apparatus according to claim 23, wherein said luminance converter means is knee correction means for providing a knee characteristic operative on the video signal.

27. The apparatus according to claim 26, wherein said first predetermined threshold level is selected to be higher than a maximum signal level established in accordance with a color television standard.

28. The apparatus according to claim 23, further comprising gamma correction means for performing gamma correction on the gradation converted three primary color signals following the gradation conversion and adjustment by said luminance converter means and saturation converter means, respectively.

29. The apparatus according to claim 28, further comprising matrix means for generating the luminance component and color difference signals based on the gradation converted three primary color signals that have been processed by said gamma correction means.

30. The apparatus according to claim 23, further comprising input luminance level detector means for detecting the luminance level of the video signal represented by the input three primary color signals;

and gradation conversion rate detector means for detecting the gradation conversion rate from the detected luminance level.

31. The apparatus according to claim 30, further comprising gradation conversion luminance level detector means for detecting the luminance level of the video signal represented by the gradation converted three primary color signals;

and level control value detector means for determining, based on the detected gradation converted luminance level, a level control value such that the maximum level of the gradation converted three primary color signals is adjusted by said saturation converter means to substantially coincide with the first predetermined threshold level, said saturation converter means adjusting the respective levels of the remaining gradation converted primary color signals as a function of the level control value.

32. The apparatus according to claim 23, further comprising gradation conversion luminance level detector means for detecting the luminance level of the video signal represented by the gradation converted three primary color signals;

and level control value detector means for determining, based on the detected gradation converted luminance level, a level control value such that the maximum level of the gradation converted three primary color signals is adjusted by said saturation converter means to substantially coincide with the first predetermined threshold level, said saturation converter means adjusting the respective levels of the remaining gradation converted primary color signals as a function of the level control value.

33. The apparatus according to claim 23, further comprising saturation conversion rate detector means for detecting a saturation conversion rate used in adjusting the saturation component of the video signal represented by the gradation converted three primary color signals such that the maximum level of at least one gradation converted primary color signal substantially coincides with the first predetermined threshold level, said saturation converter means adjusting the respective levels of the remaining gradation converted primary color signals using the detected saturation conversion rate.

34. The apparatus according to claim 23, further comprising saturation conversion rate detector means for detecting the saturation conversion rate used in adjusting the saturation component of the video signal represented by the gradation converted three primary color signals such that the maximum level of at least one gradation converted primary color signal substantially coincides with the first predetermined threshold level;

and saturation conversion rate input means for supplying a user selectable saturation conversion rate;

wherein said saturation converter means adjusts the respective levels of the gradation converted three primary color signals using the lowest rate selected from the detected saturation conversion rate or the user selectable saturation conversion rate.

35. A video signal processor for processing a video signal formed of luminance and chrominance components, said chrominance component defined by hue and saturation components, said video signal processor comprising:

generator means for generating input three primary color signals having respective levels and representing the video signal;

luminance converter means for generating gradation converted three primary color signals by gradation converting the respective levels of the input three primary color signals using one gradation conversion rate without affecting the hue and saturation components; and

saturation converter means for adjusting, as part of a knee compression operation, a maximum level detected from the gradation converted three primary color signals when the detected maximum level exceeds a first predetermined threshold level, wherein the detected maximum level is adjusted to substantially coincide with the first predetermined threshold level without affecting the hue component and the luminance component.

36. The apparatus according to claim 35, wherein the three respective levels are gradation converted when the luminance component exceeds a second predetermined threshold level.

37. The apparatus according to claim 36, wherein said first predetermined threshold level is selected to be higher than said second predetermined threshold level.

38. The apparatus according to claim 35, wherein said luminance converter means is knee correction means for providing a knee characteristic operative on the video signal.

39. The apparatus according to claim 38, wherein said first predetermined threshold level is selected to be higher than a maximum signal level established in accordance with a color television standard.

40. The apparatus according to claim 35, further comprising gamma correction means for performing gamma correction on the gradation converted three primary color signals following the gradation conversion and adjustment by said luminance converter means and saturation converter means, respectively.

41. The apparatus according to claim 40, further comprising matrix means for generating the luminance component and color difference signals from the gradation converted three primary color signals that have been processed by said gamma correction means.

42. The apparatus according to claim 35, further comprising input luminance level detector means for detecting the luminance level of the video signal represented by the input three primary color signals;

and gradation conversion rate detector means for detecting the gradation conversion rate from the detected luminance level.

43. The apparatus according to claim 42, further comprising gradation converted luminance level detector means for detecting the luminance level of the video signal represented by the gradation converted three primary color signals;

and level control value detector means for determining, based on the detected gradation converted luminance level, a level control value such that the maximum level of the gradation converted three primary color signals is adjusted by said saturation converter means to substantially coincide with the first predetermined threshold level, said saturation converter means adjusting the respective levels of the remaining gradation converted primary color signals as a function of the level control value.

44. The apparatus according to claim 35, further comprising gradation converted luminance level detector means for detecting the luminance level of the video signal represented by the gradation converted three primary color signals;

and level control value detector means for determining, based on the detected gradation converted luminance level, a level control value such that the maximum level of the gradation converted three primary color signals is adjusted by said saturation converter means to substantially coincide with the first predetermined threshold level, said saturation converter means adjusting the respective levels of the remaining gradation converted primary color signals as a function of the level control value.

45. The apparatus according to claim 35, further comprising saturation conversion rate detector means for detecting a saturation conversion rate used in adjusting the saturation component of the video signal represented by the gradation converted three primary color signals such that the maximum level of at least one gradation converted primary color signal substantially coincides with the first predetermined threshold level, said saturation converter means adjusting the respective levels of the remaining gradation converted primary color signals using the detected saturation conversion rate.

46. The apparatus according to claim 35, further comprising saturation conversion rate detector means for detecting the saturation conversion rate used in adjusting the saturation component of the video signal represented by the gradation converted three primary color signals such that the maximum level of at least one gradation converted primary color signal substantially coincides with the first predetermined threshold level;

and saturation conversion rate input means for supplying a user selectable saturation conversion rate;

wherein said saturation converter means adjusts the respective levels of the gradation converted three primary color signals using the lowest rate selected from the detected saturation conversion rate or the user selectable saturation conversion rate.

47. A method for compressing a level of a video signal formed of luminance and chrominance components, said chrominance component defined by hue and saturation components, the video signal being represented by three primary color signals having respective levels, said method comprising the steps of:

compressing, during a first stage of a knee compression operation, the respective levels of the three primary color signals using one compression rate to generate compressed three primary color signals without affecting the hue and saturation components; and

adjusting, during a second stage of said knee compression operation, a maximum level of at least one compressed primary color signal to substantially coincide with a predetermined threshold level without affecting the hue component and the luminance component when the maximum level of said one compressed primary color signal exceeds the predetermined threshold level.

48. A method for converting gradations of a video signal formed of luminance and chrominance components, said chrominance component defined by hue and saturation components, the video signal being represented by three primary color signals, said method comprising the steps of:

converting the gradations of the three primary color signals using one compression rate to generate gradation converted three primary color signals without affecting the hue and saturation components; and

adjusting, as part of a knee compression operation, a maximum level of at least one gradation converted primary color signal to substantially coincide with a predetermined threshold level without affecting the hue component and the luminance component when the maximum level of said one gradation converted primary color signal exceeds the predetermined threshold level.

49. A video camera for generating an output video signal by converting gradations of an input video signal, comprising:

cumulative frequency distribution detector means for detecting a cumulative frequency distribution of the input video signal;

first conversion data generator means for generating first conversion data for converting a level of the input video signal to a level of the output video signal based on the cumulative frequency distribution;

second conversion data generator means for generating second conversion data by adjusting the first conversion data, wherein the second conversion data is obtained by making the output video signal level, converted with the first conversion data, substantially equal to the input video signal level; and

level converter means for converting the input video signal level to the output video signal level using the second conversion data.

50. The apparatus according to claim 49, wherein the output video signal comprises high luminance components, and further comprising high luminance compression means for compressing the high luminance components outputted from said level converter means.

51. The apparatus according to claim 49, wherein the input video signal includes at least first and second video portions and a vertical blanking interval;

and wherein the cumulative frequency distribution is detected during the first video portion, and the first and second conversion data are generated during the vertical blanking interval based on the cumulative frequency distribution detected during the second video portion preceding the first video portion.

52. The apparatus according to claim 49, wherein the input video signal includes a plurality of video portions and at least one vertical blanking interval;

and wherein the first and second conversion data are generated during the vertical blanking interval based on a plurality of cumulative frequency distributions detected during the plurality of video portions.

53. A video signal processor for processing a video signal by converting gradations of an input video signal to obtain an output video signal, comprising:

cumulative frequency distribution detector means for detecting a cumulative frequency distribution of the input video signal;

first conversion data generator means for generating first conversion data for converting a level of the input video signal to a level of the output video signal based on the cumulative frequency distribution;

second conversion data generator means for generating second conversion data by adjusting the first conversion data, wherein the second conversion data is obtained by making the output video signal level, converted with the first conversion data, substantially equal to the input video signal level; and

level converter means for converting the input video signal level to the output video signal level using the second conversion data.

54. The apparatus according to claim 53, wherein the output video signal comprises high luminance components, and further comprising high luminance compression means for compressing the high luminance components outputted from said level converter means.

55. The apparatus according to claim 53, wherein the input video signal includes at least first and second video portions and a vertical blanking interval;

and wherein the cumulative frequency distribution is detected during the first video portion, and the first and second conversion data are generated during the vertical blanking interval based on the cumulative frequency distribution detected during the second video portion preceding the first video portion.

56. The apparatus according to claim 53, wherein the input video signal includes a plurality of, video portions and at least one vertical blanking interval;

and wherein the first and second conversion data are generated during the vertical blanking interval based on a plurality of cumulative frequency distributions detected during the plurality of video portions.

57. A video camera for generating an output video signal by converting gradations of an input video signal which includes a high data occurrence period and a low data occurrence period, comprising:

detector means for detecting signal level distribution data of an input video signal during the high data occurrence period, and for detecting conversion data for converting a gradation of the input video signal during the low data occurrence period based on the signal level distribution data;

control means for controlling said detector means in accordance with the input video signal;

memory means for storing at least the signal level distribution data and conversion data; and

gradation converter means for converting the gradation of the input video signal based on the conversion data.

58. The apparatus according to claim 57, wherein said control means enables said detector means to detect the conversion data in response to the signal level distribution data being stored in said memory means.

59. The apparatus according to claim 58, wherein the conversion data is operative to inhibit the gradation conversion with respect to a predetermined level of the input video signal.

60. The apparatus according to claim 58, wherein the input video signal includes a black code, and the conversion data is operative to inhibit the gradation conversion with respect to the black code.

61. A video signal processor for processing a video signal by converting gradations of an input video signal, which includes a high data occurrence period and a low data occurrence period, to obtain an output video signal, comprising:

detector means for detecting signal level distribution data of an input video signal during the high data occurrence period, and for detecting conversion data for converting a gradation of the input video signal during the low data occurrence period based on the signal level distribution data;

control means for controlling said detector means in accordance with the input video signal;

memory means for storing at least the signal level distribution data and conversion data; and

gradation converter means for converting the gradation of the input video signal based on the conversion data.

62. The apparatus according to claim 61, wherein said control means enables said detector means to detect the conversion data in response to the signal level distribution data being stored in said memory means.

63. The apparatus according to claim 62, wherein the conversion data is operative to inhibit the gradation conversion with respect to a predetermined level of the input video signal.

64. The apparatus according to claim 62, wherein the input video signal includes a black code, and the conversion data is operative to inhibit the gradation conversion with respect to the black code.

65. A method for converting gradations of an input video signal, which includes a high data occurrence period and a low data occurrence period, to obtain an output video signal, comprising the steps of:

detecting a cumulative frequency distribution of the input video signal;

generating first conversion data for converting a level of the input video signal to a level of the output video signal based on the cumulative frequency distribution;

generating second conversion data by adjusting the first conversion data, wherein the second conversion data is obtained by making the output video signal level, converted with the first conversion data, substantially equal to the input video signal level; and

converting the input video signal level to the output video signal level using the second conversion data.