Methods and systems for dynamic color equalization

• US 7,991,225 B2
• Filed: 03/05/2007
• Issued: 08/02/2011
• Est. Priority Date: 03/03/2006
• Status: Expired due to Fees

• Current Assignee: University of Alaska
• Original Assignee: University of Alaska
• Inventors: Stahlke, Daniel
• Primary Examiner(s): Mehta; Bhavesh M
• Assistant Examiner(s): Krasnic; Bernard
• Application Number:
  US11/682,205
• Publication Number:
  US 20070206854A1
• Time in Patent Office: 1,611 Days
• Field of Search: 382/167, 382/168, 382/162, 382/169, 382/170, 382/276
• US Class Current: 382/167
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06T 5/92 based on global image properties

Abstract

Disclosed herein are methods and systems for dynamic color equalization that can be used for image viewer applications. The methods and systems described involve linking enhancement parameters to a changing viewport. When a large image is being viewed, only a portion of the image can fit in a viewer window at a time. A viewport can be defined as the portion of image data that is displayed on a screen. Scrolling or zooming the image can be described as moving the viewport.

Claims

1. A computer implemented method for color equalization, comprising:

(a) determining, by a computer, image statistics for at least a first portion of an input image, wherein the image statistics comprise a histogram;

(b) generating, by the computer, a transformation function for the first portion of the input image based at least in part on the image statistics;

(c) enhancing, by performing histogram equalization or contrast stretch by the computer, the first portion of the input image using the transformation function;

(d) displaying, by the computer, the enhanced first portion of the input image; and

(e) dynamically and continually repeating, by the computer, steps (a)-(d) for at least a second portion of the input image during an operation that determines the second portion of the input image, wherein the operation is at least one of zooming in, zooming out, or panning.

2. The method of claim 1, wherein the step of determining, by the computer, the image statistics for at least the first portion of the input image, wherein the image statistics comprise a histogram, comprises determining the histogram of the first portion of the input image, wherein the histogram represents a number of pixels of each of a plurality of color values in the first portion of the input image.

3. The method of claim 2, wherein the step of generating, by the computer, the transformation function further comprises receiving a pre-determined target histogram and generating the transformation function based at least in part on the histogram and the pre-determined target histogram.

4. The method of claim 3, wherein the pre-determined target histogram represents a uniform color distribution.

5. The method of claim 3, wherein the pre-determined target histogram represents a Gaussian color distribution.

6. The method of claim 1, further comprising:

dividing by the computer the input image into at least a first tile and second tile, wherein each of the first tile and the second tiles comprises at least two pixels each having a respective color value;

determining, by the computer, first tile statistics for the first tile; and

determining, by the computer, second tile statistics for the second tile,

wherein the steps of dividing, by the computer, the input image and determining by the computer the first statistics and the second tile statistics occur prior to determining, by the computer, image statistics for at least the first portion of the input image.

7. The method of claim 6, wherein the first portion of the input image comprises at least one of the first tile and the second tiles, and wherein the step of determining by the computer image statistics for at least a first portion of the input image is based at least in part on the tile statistics of the respective one or more tiles of the first portion of the input image.

8. The method of claim 7, wherein the step of determining by the computer the first tile statistics comprises determining by the computer a first tile histogram of the first tile and the step of determining by the computer the second tile statistics comprises determining by the computer a second tile histogram of the second tile, wherein the first tile histogram and second tile histograms represent a number of pixels of each of a plurality of color values in each of the respective first tile and second tiles.

9. The method of claim 8, wherein the step of determining by the computer image statistics for the first portion of the input image comprises determining by the computer a histogram of the first portion of the input image based at least in part on the tile histogram of the respective one or more tiles of the first portion of the input image.

10. The method of claim 9, further comprising receiving by the computer a pre-determined target histogram, wherein the step of generating, by the computer, a transformation function for the first portion of the input image comprises generating, by the computer, a transformation function based on the histogram of the first portion of the input image and the pre-determined target histogram.

11. The method of claim 1, wherein the first portion of the input image is a subset of the second portion of the input image.

12. The method of claim 1, wherein the second portion of the input image is a subset of the first portion of the input image.

13. A computer readable non-transitory storage medium with computer executable instructions embodied thereon for dynamic color equalization, comprising:

(a) determining image statistics for at least a first portion of an input image, wherein the image statistics comprise a histogram;

(b) generating a transformation function for the first portion of the input image based at least in part on the image statistics;

(c) enhancing, by performing histogram equalization or contrast stretch, the first portion of the input image using the transformation function;

(d) displaying the enhanced first portion of the input image; and

(e) dynamically and continually repeating steps (a)-(d) for at least a second portion of the input image in response to a received command during an operation on the input image that determines at least in part the second portion of the input image, wherein the operation is at least one of a zoom operation or a pan operation.

14. The computer readable non-transitory storage medium of claim 13, wherein the step of determining, by the computer, the image statistics for at least the first portion of the input image, wherein the image statistics comprise a histogram, comprises determining the histogram of the first portion of the input image, wherein the histogram represents a number of pixels of each of a plurality of color values in the first portion of the input image.

15. The computer readable non-transitory storage medium of claim 14, wherein the step of generating, by the computer, the transformation function further comprises receiving a pre-determined target histogram and generating the transformation function based at least in part on the histogram and the pre-determined target histogram.

16. The computer readable non-transitory storage medium of claim 15, wherein the pre-determined target histogram represents a uniform color distribution.

17. The computer readable non-transitory storage medium of claim 13, wherein the first portion of the input image is a subset of the second portion of the input image.

18. The computer readable non-transitory storage medium of claim 13, wherein the second portion of the input image is a subset of the first portion of the input image.

19. A system, comprising:

a memory configured for storing image data comprising an input image;

a processor, coupled to the memory, wherein the processor is configured to perform the steps of;

(a) receiving an input image;

(b) determining image statistics for at least a first portion of the input image, wherein the image statistics comprise a histogram;

(c) generating a transformation function for the first portion of the input image based at least in part on the image statistics;

(d) enhancing, by performing histogram equalization or contrast stretch, the first portion of the input image using the transformation function;

(e) displaying the enhanced first portion of the input image; and

(f) dynamically and continually repeating steps (b)-(e) for at least a second portion of the input image during an operation on the input image, wherein the operation defines dynamically the second portion of the input image and comprises at least one of a zoom operation or a pan operation.

20. The system of claim 19, wherein the step of determining, by the computer, the image statistics for at least the first portion of the input image, wherein the image statistics comprise a histogram, comprises determining the histogram of the first portion of the input image, wherein the histogram represents a number of pixels of each of a plurality of color values in the first portion of the input image.

21. The system of claim 20, wherein the step of generating, by the computer, the transformation function further comprises receiving a pre-determined target histogram and generating the transformation function based at least in part on the histogram and the pre-determined target histogram.

22. The system of claim 21, wherein the pre-determined target histogram represents a uniform color distribution.

23. The system of claim 19, wherein the first portion of the input image is a subset of the second portion of the input image.

24. The system of claim 19, wherein the second portion of the input image is a subset of the first portion of the input image.