Enhancing contrast

• US 20060088275A1
• Filed: 10/25/2004
• Published: 04/27/2006
• Est. Priority Date: 10/25/2004
• Status: Active Grant

• Current Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Original Assignee: Bose Corporation
• Inventors: O'Connell, Michael, Berardi, William, O'Dea, Stephen R.
• Granted Patent: US 7,545,397 B2
• Time in Patent Office: Days
• US Class Current: 386/304
• CPC Class Codes: H04N 21/42202 environmental sensors, e.g. for detecting temperature, luminosity, pressure, earthquakes
• CPC Class Codes: H04N 21/4318 by altering the content in the rendering process, e.g. blanking, blurring or masking an image region image enhancement or restoration in general G06T5/00
• CPC Class Codes: H04N 5/58 in dependence upon ambient light
• CPC Class Codes: H04N 5/74 Projection arrangements for image reproduction, e.g. using eidophor

Abstract

Video processing for enhancing contrast includes detecting the ambient light levels on a display, performing local contrast enhancement processing to emphasize the luminance component based on the detected ambient light levels to provide a processed video signal, and presenting the processed video signal on the display.

Claims

1. A method of processing a video signal for a display, comprising:

detecting ambient light levels;

performing local contrast enhancement processing on said video signal based on the detected ambient light levels to provide a processed video signal;

presenting said processed video signal to said display.

2. The method of claim 1 wherein local contrast enhancement is performed on a luminance component of said video signal.

3. The method of claim 2 wherein said luminance component is associated with object shapes and textures;

4. The method of claim 1, wherein performing local contrast enhancement is on a pixel-by-pixel basis.

5. The method of claim 1, wherein the local contrast enhancement is based on a spatial filter.

6. The method of claim 5, wherein the spatial filter is two dimensional spatial filter.

7. The method of claim 5, wherein said spatial filter varies based on detected ambient light levels.

8. The method of claim 1, wherein said local contrast enhancement includes all-pass filtering and low-pass filtering said video signal and subtracting the low-pass filtered component from the all-pass filtered component to obtain high frequency components.

9. The method of claim 1, wherein said local contrast enhancement processing further includes determining an enhancement processor for each pixel depending on the detected ambient light levels.

10. The method of claim 9, wherein said local contrast enhancement processing is characterized by a static gain.

11. The method of claim 9, wherein said local contrast enhancement processing is characterized a dynamic gain.

12. The method of claim 9, wherein said local contrast enhancement processing is adjusted dependent on the comparison of pixel image brightness to the detected ambient light levels.

13. The method of claim 10, wherein said static gain increases when the image brightness in the pixel is less than the detected ambient light level and decreases when the image brightness in the pixel is greater than the detected ambient light level.

14. The method of claim 12, wherein the adjusting of said enhancement processing is controlled by an enhancement control variable.

15. The method of claim 14, wherein said enhancement control variable has a functional representation with values increasing when the image brightness in the pixel is less than the detected ambient light level and decreasing when the image brightness in the pixel is greater than the detected ambient light level.

16. The method of claim 9, wherein said enhancement processing further includes a low-pass processing component and a high-pass processing component.

17. The method of claim 1, wherein performing local contrast enhancement processing further is followed by a luminance adjustment processing dependent on comparison of pixel image brightness with the detected ambient light level.

18. The method of claim 1, wherein performing local contrast enhancement processing is preceded by a luminance adjustment process dependent on comparison of pixel image brightness with the detected ambient light level.

19. The method of claim 1, wherein performing local contrast enhancement processing is preceded and followed by two luminance adjustment processes dependent on comparison of pixel image brightness with the detected ambient light level.

20. The method of claim 19, wherein said two luminance adjustment processes are substantially complementary.

21. The method of claim 17, wherein said luminance adjustment processing is controlled in accordance with an input-output luminance mapping table dependent on the detected ambient light level.

22. The method of claim 18, wherein said luminance adjustment processing is controlled in accordance with an input-output luminance mapping table dependent on the detected ambient light level.

23. The method of claim 19, wherein said luminance adjustment processing is controlled in accordance with an input-output luminance mapping table dependent on the detected ambient light level.

24. The method of claim 21, wherein said input-output luminance mapping table further includes a set of mapping curves generated by a functional representation.

25. The method of claim 24, wherein said functional representation is a gamma function.

26. A method of ambient light level estimation for a video presentation system having a display device with a screen for presenting images, comprising:

measuring the light intensity in one or more areas surrounding said screen;

estimating the ambient light level falling on said screen based on said measured surrounding light intensity and on a relationship between the measured surrounding light intensities and said ambient light level by comparing the measured surrounding light intensities in said one or more areas and with that on the screen.

27. The method of claim 26, wherein said relationship is established by a lookup curve.

28. The method of claim 26, wherein said surrounding light intensities are measured when the display device is off.

29. A method of ambient light level detection for a video presentation system having a display device with a screen for presenting images, comprising:

monitoring the light intensity on said screen; and

separating ambient light intensity from said monitored light intensity by distinguishing ambient light from the light generated by said display device.

30. The method of claim 29, wherein said separating employs an optical method determining the polarizing angle of light generated by said display device,

and separating said ambient light intensity by sensing light orthogonally polarized to said polarizing angle.

31. The method of claim 29, wherein said separating employs a spectral filtering method determining colors of said display device and separating said ambient light intensity by blocking the display device colors from the monitored light intensity.

32. A method of ambient light level detection for a video presentation system including a video signal and having a display device with a screen for presenting images, comprising:

identifying the time intervals when some portion of said screen is black; and

measuring the ambient light intensity in said some portion of said screen.

33. The method of claim 32 wherein identifying the time intervals is by monitoring said screen to identify said time intervals when said screen is black.

34. The method of claim 32 wherein identifying the time intervals is by monitoring said video signal to identify said time intervals when said video signal consists of a blanking signal.

35. The method of claim 32 wherein said portion is the complete screen.

36. A method of determining a relationship between ambient light levels and display light levels for a video presentation system having a display device with a screen for presenting a video image comprising:

driving said screen using image patterns representing available luminance intensity range of said display device;

detecting ambient light levels; and

mapping the luminance intensity level within said range to the detected ambient light level.

37. A video processing system having a display and video signal comprising:

a device for detecting the ambient light levels on said display and providing a detected ambient light level signal;

a processor responsive to said detected ambient light level signal for processing said video signal, performing pixel-by-pixel contrast enhancement processing on said video signal based on the detected ambient light levels to provide a processed video signal;

and a display device having an active screen area for presenting said processed video signal on said display and surrounding areas.

38. The video processing system of claim 37, wherein said device for detecting the ambient light levels is a camera for imaging at least one of the active screen area and surrounding areas of said display device.

39. The video processing system of claim 37, wherein said device for detecting the ambient light levels is composed of one or more light sensors located near the active screen area of said display device.

40. The video processing system of claim 37, wherein said processing further includes processing with a 2-D high-pass filter.

41. The video processing system of claim 37, wherein said processing further includes an all-pass filter and a 2-D low-pass filter.

42. The video processing system of claim 41, wherein said processor includes a 2-D low-pass filter responsive to said detected ambient light signal.

43. The video processing system of claim 37, wherein said processor further includes a comparator for comparing the video signal pixel brightness to the detected ambient light levels and providing a pixel based contrast enhancement processing signal based on said comparison.