Methods and systems for image enhancement

• US 8,155,434 B2
• Filed: 10/30/2007
• Issued: 04/10/2012
• Est. Priority Date: 10/30/2007
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Laboratories of America Incorporated (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Kerofsky, Louis J., Feng, Xiao-Fan, Pan, Hao, Daly, Scott J.
• Primary Examiner(s): CHANG, JON CARLTON
• Application Number:
  US11/929,918
• Publication Number:
  US 20090109233A1
• Time in Patent Office: 1,624 Days
• Field of Search: 382/162, 382/254, 382/260, 382/263, 382/264, 382/274
• US Class Current: 382/162
• CPC Class Codes: G09G 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• CPC Class Codes: G09G 2340/16 Determination of a pixel data signal depending on the signal applied in the previous frame
• CPC Class Codes: G09G 3/2003 Display of colours specific for liquid crystal displays G09G3/3607
• CPC Class Codes: G09G 3/2044 using dithering
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336

Abstract

Embodiments of the present invention relate to systems and methods for image enhancement. Some embodiments comprise color detection, color mapping and differential processing based on color characteristics. Some embodiments comprise tonescale processing. Some embodiments comprise application of dither pattern noise to an image to reduce contouring artifacts.

Claims

1. A method for adjusting image characteristics, said method comprising:

a) processing an image to create a low-pass (LP) image and a high-pass (HP) image;

b) detecting skin-color regions in said LP image;

c) creating a skin-color map of said skin-color regions;

d) refining said skin-color map;

e) differentially processing said LP image wherein a skin-color region identified with said skin-color map is processed differently than a non-skin-color region, thereby creating a color-enhanced LP image; and

f) enhancing the brightness of said differentially-processed LP image based on an associated selected one of a plurality of backlight levels and subsequently combining said differentially-processed LP image with said HP image.

2. A method as described in claim 1 further comprising applying a tonescale operation to said color-enhanced LP image thereby creating an adjusted, color-enhanced LP image.

3. A method as described in claim 1 further comprising combining said color-enhanced LP image with said HP image to create a combined, color-enhanced image and combining said combined, color-enhanced image with a dither pattern array that is temporally high-pass and spatially high-pass thereby creating a combined, color-enhanced, dither-enhanced image.

4. A method as described in claim 1 wherein said refining said skin-color map comprises adjusting map values when pixels are spatially close and their colors are within a specified distance in color space.

5. A method as described in claim 1 wherein said detecting skin-color regions comprises matching pixel color values to a pre-defined look-up table (LUT), that correlates skin-color likelihood values with color values.

6. A method for adjusting image characteristics, said method comprising:

a) processing an image to create a low-pass (LP) image and a high-pass (HP) image;

b) applying a tonescale operation to said LP image thereby creating an adjusted LP image;

c) combining said adjusted LP image with said HP image thereby creating a combined, adjusted image; and

d) combining said combined, adjusted image with a dither pattern array that is temporally high-pass and spatially high-pass thereby creating a combined, dither-enhanced image.

7. A method as described in claim 6 further comprising applying a gain operation to said HP image before said combining.

8. A method as described in claim 6 wherein said dither pattern array is created with a spatial, cross-color-channel and cross-temporal-frame repellent function.

9. A method as described in claim 6 wherein said tonescale operation comprises applying a tonescale function that comprises a roll-off curve.

10. A method for adjusting image characteristics, said method comprising:

a) processing an image to create a low-pass (LP) image and a high-pass (HP) image;

b) detecting skin-color regions in said LP image;

c) creating a skin-color map of said skin-color regions;

d) refining said skin-color map; and

e) differentially processing said LP image wherein a skin-color region identified with said skin-color map is processed differently than a non-skin-color region, thereby creating a color-enhanced LP image;

f) applying a tonescale operation to said color-enhanced LP image thereby creating an adjusted LP image, wherein said tonescale operation is dependent on a backlight level selection; and

g) combining said adjusted LP image with said HP image thereby creating a combined, adjusted image.

11. A method as described in claim 10 further comprising combining said combined, adjusted image with a dither pattern array that is temporally high-pass and spatially high-pass thereby creating a combined, dither-enhanced image.

12. A method as described in claim 11 wherein said dither pattern array is created with a spatial, cross-color-channel and cross-temporal-frame repellent function.

13. A method as described in claim 10 wherein said refining said skin-color map comprises adjusting map values when pixels are spatially close and pixels their colors are within a specified distance in color space.

14. A method as described in claim 10 wherein said detecting skin-color regions comprises matching pixel color values to a pre-defined look-up table (LUT), that correlates skin-color likelihood values with color values.

15. A method as described in claim 10 further comprising applying a gain operation to said HP image before said combining.

16. A method as described in claim 10 wherein said tonescale operation comprises applying a tonescale function that comprises a roll-off curve.

17. A method as described in claim 10 wherein said tonescale operation comprises applying a gain adjustment to a range of code values below an MFP point and applying a roll-off curve to code values above said MFP point.

18. A method as described in claim 10 further comprising generating an image histogram and selecting a display backlight level based on a histogram from a previous image frame.

19. A method as described in claim 10 further comprising generating an image histogram and selecting a display backlight level based on a histogram from a previous, original, unfiltered image frame.

20. A method as described in claim 10 wherein further comprising coring said HP image before said combining.

21. A method for adjusting image characteristics, said method comprising:

a) processing an image to create a low-pass (LP) image and a high-pass (HP) image;

b) detecting skin-color regions in said LP image;

c) creating a skin-color map of said skin-color regions;

d) refining said skin-color map; and

e) differentially processing said LP image wherein a skin-color region identified with said skin-color map is processed differently than a non-skin-color region, thereby creating a color-enhanced LP image;

f) applying a tonescale operation to said color-enhanced LP image thereby creating an adjusted LP image, wherein said tonescale operation comprises applying a tonescale function that comprises a roll-off curve; and

g) combining said adjusted LP image with said HP image thereby creating a combined, adjusted image.

22. A method for adjusting image characteristics, said method comprising:

a) processing an image to create a low-pass (LP) image and a high-pass (HP) image;

b) detecting skin-color regions in said LP image;

c) creating a skin-color map of said skin-color regions;

d) refining said skin-color map; and

e) differentially processing said LP image wherein a skin-color region identified with said skin-color map is processed differently than a non-skin-color region, thereby creating a color-enhanced LP image;

f) applying a tonescale operation to said color-enhanced LP image thereby creating an adjusted LP image, wherein said tonescale operation comprises applying a gain adjustment to a range of code values below a Maximum Fidelity Point and applying a roll-off curve to code values above said Maximum Fidelity Point; and

g) combining said adjusted LP image with said HP image thereby creating a combined, adjusted image.