System and method for dynamically enhanced color space

• US 7,127,123 B2
• Filed: 06/24/2002
• Issued: 10/24/2006
• Est. Priority Date: 12/21/2001
• Status: Active Grant

• Current Assignee: Jaldi Semiconductor Corporation (Pixelworks Incorporated)
• Original Assignee: Jaldi Semiconductor Corporation (Pixelworks Incorporated)
• Inventors: Wredenhagen, G. Finn, Ang, Peter
• Primary Examiner(s): Mehta, Bhavesh M.
• Assistant Examiner(s): TUCKER, WESLEY J
• Application Number:
  US10/177,766
• Publication Number:
  US 20030117654A1
• Time in Patent Office: 1,583 Days
• Field of Search: 382/169, 382/274
• US Class Current: 382/274
• CPC Class Codes: H04N 1/4074 using histograms

Abstract

Contrast in an image is enhanced by mapping an input intensity value to an output intensity value in accordance with a mapping function. A mean intensity value of the image is determined. Co-ordinates of the mapping function are calculated in accordance with the mean intensity value and a plurality of predefined parameters. The mapping function is applied to the input intensity value for determining the output intensity, wherein the mapping function is generated dynamically for each image.

Claims

1. A method for enhancing contrast in a plurality of images in a video sequence by mapping an input intensity value to an output intensity value in accordance with a mapping function, the method comprising the steps of:

(a) determining a mean intensity value of the image;

(b) calculating the mapping function including left, right, middle, and principal range, the principal range being contained within the middle range;

(c) applying the mapping function to the input intensity value for determining said output intensity responsive to determining the modality;

(d) determining that the image is likely unimodal if a percentage of image pixels that lie in the principal range is above a first predefined threshold; and

(e) determining that the image is likely bimodal if the percentage of image pixels that lie in the principal range is below a second predefined threshold;

(f) dynamically generating the mapping function for each image in the video sequence.

2. A method as defined in claim 1, wherein the method further includes the steps of

(g) calculating gains for the mapping function in accordance with the percentage of image pixels that lie in said the principal range.

3. A method as defined in claim 2, wherein calculating the mapping function comprises calculating a left segment, a middle segment, and a right segment, the left and right segments having again less than unity and the middle segment having a gain larger than unity.

4. A method as defined in claim 3, wherein decreasing the gains for said left and right segments and increasing the gain for the middle segment as the percentage of image pixels that lie in the principal range increases.

5. A method as defined in claim 3, wherein the gains for said left and right segments are increased and the gain for said middle segment is decreased as the percentage of image pixels that lie in the principal range decreases.

6. A method as defined in claim 1 wherein the first predefined threshold is equivalent to the second predefined threshold.

7. A method as defined in claim 3, wherein the mapping function is piecewise linear.

8. A method as defined in claim 3, wherein the mapping function is stored in equation form and applied to the input intensity value to obtain the output intensity value for each pixel in each image.

9. A method as defined in claim 3, wherein the mapping function is stored in a table by calculating corresponding output intensity values for all possible input intensity values and applied to the input intensity value by looking up the input intensity value in the table and retrieving the corresponding output intensity value.

10. A method as defined in claim 1, wherein a piecewise linear offset is added to the intensity for increasing the overall luminance of at least one of the plurality of images.

11. A method as defined in claim 1, wherein the contrast is further enhanced by applying a static mapping function to a colour channel of at least one of the plurality of images.

12. A method as defined in claim 1, wherein the contrast is further enhanced by applying a static mapping function to a hue channel of at least one of the plurality of images.

13. A method as defined in claim 1, including calculating the mapping function in accordance with user-defined preferences.

14. A system for enhancing contrast in a plurality of images in a video sequence by mapping an input intensity value to an output intensity value in accordance with a mapping function, the system comprising:

histogram hardware comprising a plurality of counters, comparators, and control logic to generate a histogram and to calculate a mean intensity value responsive to the histogram; and

a processor to calculate left, right, middle, and principal ranges of the mapping function in accordance with the mean intensity value and a plurality of predefined parameters, to determine a modality of each image responsive to the principal range, and to apply the mapping function to the input intensity value to determine the output intensity responsive to the modality;

where the principal range is contained within the middle range; and

wherein the mapping function is generated dynamically for each image in the video sequence;

where the processor is adapted to determine that the image is likely unimodal if a percentage of image pixels that lie in the principal range is above a first predefined threshold;

where the processor is adapted to determine that the image is likely bimodal if the percentage of image pixels that lie in the principal range is below a second predefined threshold.

15. The system of claim 14 where the processor is adapted to calculate gains for the mapping function in accordance with the percentage of image pixels that lie in the principal range.

16. The system of claim 15 where the processor is adapted to calculate a left segment, a middle segment, and a right segment, the left and right segments having a gain less than unity and the middle segment having a gain larger than unity.

17. The system of claim 16 where the processor is adapted to decrease gains for the left and right segments and to increase gain for the middle segment as the percentage of image pixels that lie in the principal range increases.

18. The system of claim 16 where the processor is adapted to increase gains for the left and right segments and to decrease the gain for middle segment as the percentage of image pixels that lie in the principal range decreases.

19. The system of claim 14 where the first predefined threshold is equivalent to the second predefined threshold.

20. The system of claim 14 where the mapping function is piecewise linear.

21. The system of claim 14 where the mapping function is stored in equation form and applied to the input intensity value to obtain the output intensity value for each pixel in each image.

22. The system of claim 14 where the mapping function is stored in a table by calculating corresponding output intensity values for all possible input intensity values and applied to the input intensity value by looking up the input intensity value in the table and retrieving the corresponding output intensity value.

23. The system of claim 14 where the processor is adapted to add a piecewise linear offset to the intensity for increasing the overall luminance of at least one of the plurality of images.