Systems and methods for color preservation with image tone scale corrections

• US 20080024517A1
• Filed: 07/28/2006
• Published: 01/31/2008
• Est. Priority Date: 07/28/2006
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Kerofsky, Louis Joseph
• Granted Patent: US 7,515,160 B2
• Time in Patent Office: Days
• US Class Current: 345/600
• CPC Class Codes: G09G 2320/0271 Adjustment of the gradation levels within the range of the gradation scale, e.g. by redistribution or clipping
• CPC Class Codes: G09G 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• CPC Class Codes: G09G 2320/0653 Controlling or limiting the speed of brightness adjustment of the illumination source
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2360/144 the light being ambient light
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 3/2007 Display of intermediate tones
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: G09G 5/02 characterised by the way in which colour is displayed details of colour display specific for CRTs G09G1/28; specific for flat matrix panels other than liquid crystal displays G09G3/2003; specific for liquid crystal displays G09G3/3607

Abstract

Embodiments of the present invention comprise systems and methods for generating and applying image tone scale corrections with improved color fidelity.

Claims

1. A method for adjusting image code values, said method comprising:

a) determining a first code value for a first color channel of a pixel in an image;

b) determining a second code value for a second color channel of said pixel in said image;

c) determining a clipping limit, which said first code value and said second code value may not exceed;

d) generating a code value adjustment model based on the greater of said first code value and said second code value wherein said adjustment model reduces said first code value and said second code value proportionally until the greater of said first code value and said second code value is complies with said clipping limit; and

adjusting said first and second code values with said code value adjustment model.

2. A method as described in claim 1 wherein said image is a low-pass (LP) version of a display image suitable for viewing by a viewer.

3. A method as described in claim 1 wherein said code value adjustment model adjusts said first and second code values by an adjustment factor equal to said clipping limit divided by the greater of said first and second code values.

4. A method as described in claim 3 wherein said adjusting comprises reducing said first and second code values proportionally by multiplying said adjustment factor by said first and second code values.

5. A method as described in claim 1 wherein said clipping limit is a display output limit.

6. A method as described in claim 1 wherein said image is an image comprising pixel values that have been modified to compensate for a reduced display source light illumination level.

7. A method for adjusting image code values, said method comprising:

a) determining a first code value for a first color channel of a pixel in an image;

b) determining a second code value for a second color channel of said pixel in said image;

c) selecting one of said first and second code values based on a code value characteristic, thereby producing a selected code value;

d) generating a code value adjustment model based on said selected code value; and

e) adjusting said first and second code values with said code value adjustment model.

8. A method as described in claim 7 wherein said code value characteristic is a maximum value.

9. A method as described in claim 7 wherein said image is a low-pass (LP) version of a display image suitable for viewing by a viewer.

10. A method as described in claim 7 wherein said code value adjustment model is also based on a source light power level to be used for displaying said adjusted pixel.

11. A method as described in claim 7 wherein said code value adjustment model increases said code values in inverse proportion to a reduction in source light power level to be used for displaying said adjusted pixel.

12. A method as described in claim 7 wherein said code value adjustment model comprises a variable gain that is reduced at higher code values to reduce clipping.

13. A method as described in claim 7 wherein said code value adjustment model comprises a photometric matching Look-Up Table (LUT).

14. A method for adjusting image code values, said method comprising:

a) filtering an image to create a low-pass (LP) version of said image;

b) generating a high-pass (HP) version of said image;

c) determining a first code value for a first color channel at a pixel in said LP version of said image;

d) determining a second code value for a second color channel at said pixel in said LP version of said image;

e) selecting one of said first and second code values based on a code value characteristic;

f) generating a code value adjustment model based on said selected code value;

g) adjusting said first and second code values with said code value adjustment model; and

h) combining said adjusted LP version of said image with said HP version of said image.

15. A method as described in claim 14 wherein said code value characteristic is a maximum value.

16. A method as described in claim 14 further comprising applying a gain map to said HP version of said image before said combining.

17. A method as described in claim 16 wherein said gain map comprises a constant gain multiplier throughout the code value range.

18. A method as described in claim 14 further comprising clipping out-of-range values after said combining by scaling the code values of all color channels by a substantially equal amount while reducing the maximum of said code values to a code value limit.

19. A method as described in claim 14 wherein said code value adjustment model adjusts said first code value and said second code value by scaling said first code value and said second code value by a substantially equal amount.

20. A method as described in claim 14 wherein said code value adjustment model is also related to a source light power level to be used for displaying said pixel.