Granted Patent B2

US 8,565,549 · App. 12/887,358 · Granted Oct 22, 2013

Inventor: Andre Leitao (Eindhoven, NL)

Assignee: NXP B.V.

Abstract

Claims (50)

1. A contrast enhancement method for an image having a plurality of pixels, the method comprising:

extracting at least one sub-band image from the image, comprising detail information at a predetermined spatial scale;

determining a first gain value for each pixel, based on pixel values of one of the image and the at least one sub-band image;

determining a second gain value for each pixel;

modifying the first gain value for each pixel using the respective second gain value; and

generating an enhanced image by applying the modified first gain values to respective pixels of at least one sub-band image and combining the result with the image,

wherein determining the first gain value for each pixel comprises:

estimating a dynamic range of the pixel values in a neighbourhood of that pixel; and

setting the first gain value in inverse relation to the dynamic range, and

wherein determining the second gain value for each pixel comprises:

estimating a probability distribution of the pixel values in the neighbourhood; and

determining the second gain value based on the amplitude of the peak of the probability distribution.

2. The method of claim 1 , wherein the first gain value for each pixel is determined based on pixel values of the at least one sub-band image.

3. The method of claim 1 , wherein the second gain value is determined such that:

a maximum gain is set when the amplitude of the peak is at an intermediate level;

a minimum gain is set when the amplitude of the peak is at a maximum level; and

an intermediate gain value is set when the amplitude of the peak is at a minimum level.

4. The method of claim 1 , wherein the estimate of the probability distribution comprises a histogram.

5. The method of claim 1 , wherein the dynamic range of the pixel values is estimated from the probability distribution.

6. A non-transitory computer readable storage medium storing a computer program comprising computer program code which when executed by a processor, adapted to perform:

extracting at least one sub-band image from the image, comprising detail information at a predetermined spatial scale;

determining a first gain value for each pixel, based on pixel values of one of the image and the at least one sub-band image;

determining a second gain value for each pixel;

modifying the first gain value for each pixel using the respective second gain value; and

generating an enhanced image by applying the modified first gain values to respective pixels of at least one sub-band image and combining the result with the image,

wherein determining the first gain value for each pixel comprises:

estimating a dynamic range of the pixel values in a neighbourhood of that pixel; and

setting the first gain value in inverse relation to the dynamic range, and

wherein determining the second gain value for each pixel comprises:

estimating a probability distribution of the pixel values in the neighbourhood; and

determining the second gain value based on the amplitude of the peak of the probability distribution.

7. The storage medium of claim 6 , wherein the first gain value for each pixel is determined based on pixel values of the at least one sub-band image.

8. The storage medium of claim 6 , wherein the second gain value is determined such that:

a maximum gain is set when the amplitude of the peak is at an intermediate level;

a minimum gain is set when the amplitude of the peak is at a maximum level; and

an intermediate gain value is set when the amplitude of the peak is at a minimum level.

9. The storage medium of claim 6 , wherein the estimate of the probability distribution comprises a histogram.

10. The storage medium of claim 6 , wherein the dynamic range of the pixel values is estimated from the probability distribution.

11. Image processing apparatus for contrast enhancement of an image having a plurality of pixels, the apparatus comprising:

filtering means, adapted to extract at least one sub-band image from the image, said at least one sub-band image comprising detail information at a predetermined spatial scale;

first gain determination means, adapted to determine a first gain value for each pixel, based on pixel values of one of the image and the at least one sub-band image;

second gain determination means, adapted to determine a second gain value for each pixel;

gain combination means, adapted to modify the first gain value using the second gain value; and

image enhancement means, adapted to generate an enhanced image by applying the modified first gain values to respective pixels of at least one sub-band image and to combine the result with the image,

wherein the first gain determination means are adapted to determine the first gain value for each pixel by:

estimating a dynamic range of the pixel values in a neighbourhood of that pixel; and

setting the first gain value in inverse relation to the dynamic range, and

wherein the second gain determination means ( 32 ) are adapted to:

estimate a probability distribution of the pixel values in the neighbourhood of the pixel; and

determine the second gain value based on the amplitude of the peak of the probability distribution.

Assignments (10)

Priority Claims (1)

Continuity (1)