Systems and methods for localized contrast enhancement

• US 9,165,210 B1
• Filed: 05/27/2014
• Issued: 10/20/2015
• Est. Priority Date: 05/27/2014
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Srinivasan, Sujith, Biswas, Mainak
• Primary Examiner(s): Dang, Duy M
• Application Number:
  US14/288,267
• Time in Patent Office: 511 Days
• US Class Current: 1/1
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06T 5/94 based on local image properties, e.g. for local contrast enhancement

Abstract

Systems and methods for improving the contrast of image frames are disclosed. In one embodiment, a system for improving the contrast of image frames includes a control module configured to create an intensity histogram for an image frame, define a set of markers on an intensity range of the histogram, assign a blend factor to each marker, calculate a blend factor for each original pixel of the image, obtain a first equalized pixel output value, calculate a final equalized pixel output value using the blend factor, the first equalized pixel output value, and an original pixel value, and output new pixel values that constitute the output image.

Claims

1. A system for improving the contrast of image frames, comprising:

a control module configured to

determine a histogram representation of an image having a plurality of pixels, each pixel having an intensity value within a range of intensity values, the histogram including the number of pixels of the image that have an intensity value for each intensity value in the range of intensity values;

define a set of markers spaced across at least a portion of the range of intensity values of the histogram of the image, each marker having an associated blend factor;

determine a pixel blend factor for each pixel of the image based on at least one marker blend factor;

determine a first equalized pixel output value for each pixel; and

calculate a final equalized pixel output value for each pixel of the image, the final equalized pixel output value for each pixel based on the pixel blend factor of that pixel, the first equalized pixel output value of that pixel, and an original pixel value of that pixel.

2. The system of claim 1 further comprising an imaging device comprising an imaging sensor.

3. The system of claim 1, wherein the control module is a component of a camera application for a mobile device.

4. The system of claim 1, wherein the markers are equally spaced across the range of intensity values.

5. The system of claim 1, wherein for a particular pixel, the pixel blend factor is based on interpolating the blend factors of two adjacent markers.

6. The system of claim 1, wherein the control module is further configured to perform contrast limited histogram equalization for each pixel of the image to obtain a first equalized pixel output value for each pixel.

7. The system of claim 1, wherein the control module is further configured to add a random noise value to the final equalized pixel output value for each pixel.

8. The system of claim 1, wherein the control module is further configured to output a modified image based on the final equalized pixel output values.

9. The system of claim 1, wherein blend factors defined in low intensity value regions of range of intensity values have a higher weight than the blend factors defined in high intensity value regions of the histogram.

10. The system of claim 1, wherein the blend factor for each marker is at least partially based on an ambient light level.

11. A method for improving the contrast of image frames, comprising:

determining a histogram representation of an image having a plurality of pixels, each pixel having an intensity value within a range of intensity values, the histogram including the number of pixels of the image that have an intensity value for each intensity value in the range of intensity values;

defining a set of markers spaced across at least a portion of the range of intensity values of the histogram of the image, each marker having an associated blend factor;

determining an pixel blend factor for each pixel of the image based on at least one marker blend factor;

determining a first equalized pixel output value for each pixel; and

calculating a final equalized pixel output value for each pixel of the image, the final equalized pixel output value for each pixel based on the pixel blend factor of that pixel, the first equalized pixel output value of that pixel, and an original pixel value of that pixel.

12. The method of claim 11, wherein the markers are equally spaced along the range of intensity values.

13. The method of claim 11, wherein for a particular pixel, the pixel blend factor is based on interpolating the blend factors of two adjacent markers.

14. The method of claim 11 further comprising performing contrast limited histogram equalization for each pixel of the image to obtain a first equalized pixel output value for each pixel.

15. The method of claim 11 further comprising adding a random noise factor to add a random noise value to the final equalized pixel output value for each pixel.

16. The method of claim 11 further comprising outputting a modified image based on the final equalized pixel output values.

17. The method of claim 11, wherein defining a set of markers spaced across at least a portion of the range of intensity values of the histogram representation of the image is at least partially determined by an ambient light level.

18. The method of claim 11, wherein determining a blend factor for each marker is at least partially determined by an ambient light level.

19. An apparatus for improving the contrast of image frames, comprising:

means for determining a histogram representation of an image having a plurality of pixels, each pixel having an intensity value within a range of intensity values, the histogram including the number of pixels of the image that have an intensity value for each intensity value in the range of intensity values;

means for defining a set of markers spaced across at least a portion of the range of intensity values of the histogram of the image, each marker having an associated blend factor;

means for determining a pixel blend factor for each pixel of the image based on at least one marker blend factor;

means for determining a first equalized pixel output value for each pixel; and

means for calculating a final equalized pixel output value for each pixel of the image, the final equalized pixel output value for each pixel based on the pixel blend factor of that pixel, the first equalized pixel output value of that pixel, and an original pixel value of that pixel.

20. A non-transitory computer-readable medium storing instructions that, when executed, cause at least one physical computer processor to perform a method for improving the contrast of image frames, the method comprising:

determining a histogram representation of an image having a plurality of pixels, each pixel having an intensity value within a range of intensity values, the histogram including the number of pixels of the image that have an intensity value for each intensity value in the range of intensity values;

defining a set of markers spaced across at least a portion of the range of intensity values of the histogram representation of the image, each marker having an associated blend factor;

determining a pixel blend factor for each pixel of the image based on at least one marker blend factor;

determining a first equalized pixel output value for each pixel; and

calculating a final equalized pixel output value for each pixel of the image, the final equalized pixel output value for each pixel based on the pixel blend factor of that pixel, the first equalized pixel output value of that pixel, and an original pixel value of that pixel.

21. The non-transitory computer-readable medium of claim 20, wherein the markers are equally spaced across the range of intensity values.

22. The non-transitory computer-readable medium of claim 20, wherein for a particular pixel, the pixel blend factor is based on interpolating the blend factors of two adjacent markers.

23. The non-transitory computer-readable medium of claim 20 further comprising performing contrast limited histogram equalization for each pixel of the image to obtain a first equalized pixel output value for each pixel.

24. The non-transitory computer-readable medium of claim 20 further comprising adding a random noise value to the final equalized pixel output value for each pixel.

25. The non-transitory computer-readable medium of claim 20 further comprising outputting a modified image based on the final equalized pixel output values.

26. The non-transitory computer-readable medium of claim 20, wherein defining a set of markers spaced across at least a portion of the range of intensity values of the histogram representation of the image is at least partially determined by an ambient light level.

27. The non-transitory computer-readable medium of claim 20, wherein determining a blend factor for each marker is at least partially determined by an ambient light level.