Method and apparatus for MPEG artifacts reduction

• US 20050129330A1
• Filed: 10/12/2004
• Published: 06/16/2005
• Est. Priority Date: 12/16/2003
• Status: Active Grant

• Current Assignee: Tamiras Per Pte Ltd LLC (Intellectual Ventures LLC)
• Original Assignee: Genesis Microchip Inc. (STMicroelectronics NV)
• Inventors: Shyshkin, Vyacheslav
• Granted Patent: US 7,346,226 B2
• Time in Patent Office: Days
• US Class Current: 382/275
• CPC Class Codes: H04N 19/117 Filters, e.g. for pre-processing or post-processing sub-band filter banks H04N19/635
• CPC Class Codes: H04N 19/14 Coding unit complexity, e.g. amount of activity or edge presence estimation H04N19/146 takes precedence
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/527 Global motion vector estimation
• CPC Class Codes: H04N 19/61 in combination with predictive coding

Abstract

Disclosed herein are methods and apparatus, including computer program products, implementing and using techniques for reducing mosquito noise in an image frame of a video signal. A window of the image frame is provided. The window includes a plurality of pixel values. One of the pixel values is selected from the pixel values in the window to define a modified window of pixel value differences. A local mean (DC) value is computed based on the pixel value differences. A mosquito noise reduction value is also computed based on the pixel value differences. An artifact attenuation factor is computed as a function of a dynamic range measure of the pixel value differences. A weighted sum of the mosquito noise reduction value and the local mean value, applying the artifact attenuation factor, and the selected pixel value, is computed to generate a modified pixel value.

Claims

1. A method of reducing mosquito noise in an image frame of a video signal, the method comprising:

providing a window of the image frame, the window including a plurality of pixel values;

subtracting a selected one of the pixel values from the pixel values in the window to define a modified window of pixel value differences;

computing a local mean (DC) value based on the pixel value differences;

computing a mosquito noise reduction value based on the pixel value differences;

computing an artifact attenuation factor as a function of a dynamic range measure of the pixel value differences; and

computing a weighted sum of the mosquito noise reduction value and the local mean value, applying the artifact attenuation factor, and the selected pixel value, to generate a modified pixel value.

2. The method of claim 1 further comprising:

limiting the pixel value differences in the modified window by a threshold.

3. The method of claim 1 wherein computing the mosquito noise reduction value includes:

computing a reducing value associated with a checkerboard pattern;

computing a weighting coefficient as a function of a variance of the pixel value differences; and

computing a weighted sum of the reducing value and the local mean value, applying the weighting coefficient, to define the mosquito noise reduction value.

4. The method of claim 1, wherein computing the local mean (DC) value includes:

applying a 2D lowpass filter to the pixel value differences.

5. The method of claim 1, wherein:

the selected pixel value is a central pixel of the window.

6. The method of claim 1, wherein:

the window is a n×

n window of pixels.

7. The method of claim 6, wherein:

n is a small odd number.

8. The method of claim 7, wherein:

n=3.

9. An apparatus for reducing mosquito noise in an image frame of a video signal, the apparatus comprising:

a windowing module configured to provide a window of the image frame, the window including a plurality of pixel values;

a subtraction module configured to subtract a selected one of the pixel values from the pixel values in the window to define a modified window of pixel value differences;

a local mean determination module configured to compute a local mean (DC) value based on the pixel value differences;

a mosquito noise reduction module configured to perform a mosquito noise reduction operation on the pixel value differences in the modified window to generate a mosquito noise reduction value;

a smooth attenuation module configured to compute an artifact attenuation factor as a function of a dynamic range measure of the pixel value differences; and

an output module configured to compute a weighted sum of the mosquito noise reduction value and the local mean value, applying the artifact attenuation factor, and the selected pixel value, to generate a modified pixel value.

10. The apparatus of claim 9, wherein the mosquito noise reduction module includes:

a limiting module configured to limit the pixel value differences in the modified window by a threshold.

11. The apparatus of claim 9, wherein the mosquito noise reduction module includes:

a highpass filter configured to compute a reducing value associated with a checkerboard pattern;

a variance module configured to compute a weighting coefficient as a function of a variance of the limited pixel value differences; and

a summing module configured to compute a weighted sum of the reducing value and the local mean value, applying the weighting coefficient, to define the mosquito noise reduction value.

12. A computer program product, stored on a processor readable medium, comprising instructions operable to cause a computer to perform a method of reducing mosquito noise in an image frame of a video signal, the method comprising:

providing a window of the image frame, the window including a plurality of pixel values;

subtracting a selected one of the pixel values from the pixel values in the window to define a modified window of pixel value differences;

computing a local mean (DC) value based on the pixel value differences;

computing a mosquito noise reduction value based on the pixel value differences;

computing an artifact attenuation factor as a function of a dynamic range measure of the pixel value differences; and

computing a weighted sum of the mosquito noise reduction value and the local mean value, applying the artifact attenuation factor, and the selected pixel value, to generate a modified pixel value.

13. The computer program product of claim 12, wherein the method further comprises:

limiting the pixel value differences in the modified window by a threshold.

14. The computer program product of claim 12, wherein computing the mosquito noise reduction value includes:

computing a reducing value associated with a checkerboard pattern;

computing a weighting coefficient as a function of a variance of the pixel value differences; and

computing a weighted sum of the reducing value and the local mean value, applying the weighting coefficient, to define the mosquito noise reduction value.

15. The computer program product of claim 12, wherein computing the local mean (DC) value includes:

applying a 2D lowpass filter to the pixel value differences.

16. The computer program product of claim 12, wherein:

the selected pixel value is a central pixel of the window.

17. The computer program product of claim 12, wherein:

the window is a n×

n window of pixels.

18. The computer program product of claim 17, wherein:

n is a small odd number.

19. The computer program product of claim 18, wherein:

n=3.