System and method for dynamically enhanced colour space

• US 20030117654A1
• Filed: 06/24/2002
• Published: 06/26/2003
• 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
• Granted Patent: US 7,127,123 B2
• Time in Patent Office: Days
• US Class Current: 358/3.21
• 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 an image by mapping an input intensity value to an output intensity value in accordance with a mapping function, said method comprising the steps of:

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

(b) calculating co-ordinates of said mapping function in accordance with said mean intensity value and a plurality of predefined parameters; and

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

wherein said mapping function is generated dynamically for each image.

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

(a) defining a principal range;

(b) determining a percentage of image pixels that lie in said principal range; and

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

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

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

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

6. A method as defined in claim 4, wherein if said percentage of image pixels that lie in said principal range is above said first predefined threshold, said image is unimodal and if said percentage of image pixels that lie in said principal range is below said second predefined threshold, said image is bimodal.

7. A method as defined in claim 5, wherein said first predefined threshold is equivalent to said second predefined threshold.

8. A method as defined in claim 3, wherein said mapping function is piecewise linear.

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

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

11. A method as defined in claim 1, wherein a piecewise linear offset is added to said intensity for increasing the overall luminance of said image.

12. A method as defined in claim 1, wherein said contrast is further enhanced by applying a static mapping function to a colour channel of said image.

13. A method as defined in claim 1, wherein said contrast is further enhanced by applying a static mapping function to a hue channel of said image.

14. A system as defined in claim 1, wherein said mapping function is further determined in accordance with user-defined preferences.

16. A system as defined in claim 11, wherein said processor further including capability of determining a percentage of image pixels that lie in a predefined principal range and calculating gains for said mapping function in accordance with said percentage of image pixels that lie in said principal range.

15. A system for enhancing contrast in an image by mapping an input intensity value to an output intensity value in accordance with a mapping function, said system comprising:

(a) a histogram comprising a plurality of counters, comparators, and control logic for determining a mean intensity value; and

(b) a processor for calculating co-ordinates of said mapping function in accordance with said mean intensity value and a plurality of predefined parameters, and for applying said mapping function to said input intensity value for determining said output intensity;

wherein said mapping function is generated dynamically for each image.