SYSTEM AND METHOD FOR MULTI-SCALE SIGMA FILTERING USING QUADRATURE MIRROR FILTERS

• US 20090214131A1
• Filed: 02/27/2008
• Published: 08/27/2009
• Est. Priority Date: 02/27/2008
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Schweid, Stuart A.
• Granted Patent: US 8,180,169 B2
• Time in Patent Office: Days
• US Class Current: 382/263
• CPC Class Codes: G06T 2207/20016 Hierarchical, coarse-to-fine, multiscale or multiresolution image processing; Pyramid transform
• CPC Class Codes: G06T 2207/20192 Edge enhancement; Edge preservation
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/70 Denoising; Smoothing
• CPC Class Codes: G06V 10/30 Noise filtering

Abstract

A first sigma filtering circuit sigma filters an image to produce a filtered image. An analysis circuit processes the sigma filtered image to produce an approximation part and a detail part. A second sigma filter circuit filters the approximation part to produce a sigma filtered approximation part. Another analysis circuit process the sigma filtered approximation part to produce a second approximation part and a second detail part. A third sigma filter circuit sigma filters the second approximation part to produce a sigma filtered second filtered approximation part. A first synthesizer synthesizes the sigma filtered second filtered approximation part and the second detailed part to produce a first reconstructed image, and a second synthesizer synthesizes the first reconstructed image and the first detail part to produce a final filtered image.

Claims

1. A method for improving the quality of a digital image comprising:

(a) obtaining a digital image;

(b) sigma filtering the image to produce a sigma filtered input image;

(c) analysis processing the sigma filtered input image to produce an approximation part and a detail part;

(d) sigma filtering the approximation part to produce a sigma filtered approximation part; and

(e) synthesizing the sigma filtered approximation part and the detail part to generate a reconstructed filtered image.

2. The method as claimed in claim 1, wherein synthesizing the filtered approximation part and the detail part comprises:

(e1) analysis processing the sigma filtered approximation part to produce a second approximation part and a second detail part;

(e2) sigma filtering the second approximation part to produce a sigma filtered second approximation part;

(e3) synthesizing the sigma filtered second approximation part and the second detailed part to produce a first reconstructed image; and

(e4) synthesizing the first reconstructed image and the first detail part to produce a final filtered image.

3. The method as claimed in claim 1, wherein the analysis processing of the sigma filtered input image and the synthesizing of the sigma filtered approximation part and the detail part have a quadrature mirror pair relationship.

4. The method as claimed in claim 1, further comprising determining a sigma value for the sigma filtering for each image.

5. The method as claimed in claim 4, wherein the determining of the sigma value comprises:

high pass filtering the image;

determining a standard deviation of the high pass filtered image; and

using the determined standard deviation as the sigma value.

6. The method as claimed in claim 5, wherein the determined standard deviation is used as the sigma value when the determined standard deviation is less than a predetermined value.

7. The method as claimed in claim 2, further comprising:

(e3a) sigma filtering first reconstructed image prior to synthesizing the first reconstructed image and the first detail part to produce a final filtered image.

8. A system for improving the quality of a digital image comprising:

a first sigma filtering circuit to sigma filter an image to produce a sigma filtered image;

an analysis circuit to process the sigma filtered image to produce an approximation part and a detail part;

a second sigma filter circuit to filter the approximation part to produce a sigma filtered approximation part; and

a synthesizer to combine the sigma filtered approximation part and the detail part to generate a reconstructed filtered image.

9. The system as claimed in claim 8, further comprising:

a sigma circuit, operatively connected to said first and second sigma filter circuits, to determine a sigma value from the image.

10. The system as claimed in claim 9, wherein said sigma circuit comprises:

a high pass filter circuit to high pass filter the image; and

a circuit to determine a standard deviation of the high pass filtered image, the determined standard deviation being the sigma value.

11. The system as claimed in claim 10, wherein the determined standard deviation is used as the sigma value when the determined standard deviation is less than a predetermined value.

12. The system as claimed in claim 8, wherein said analysis circuit and said synthesizer form a quadrature mirror pair.

13. A system for improving the quality of a digital image comprising:

a first sigma filtering circuit to sigma filter an image to produce a sigma filtered image;

a first analysis circuit to process the sigma filtered image to produce an approximation part and a detail part;

a second sigma filter circuit to filter the approximation part to produce a sigma filtered approximation part;

a second analysis circuit to process the sigma filtered approximation part to produce a second approximation part and a second detail part;

a third sigma filter circuit to sigma filter the second approximation part to produce a sigma filtered second approximation part;

a first synthesizer to synthesize the sigma filtered second approximation part and the second detailed part to produce a first reconstructed image; and

a second synthesizer to synthesize the first reconstructed image and the first detail part to produce a final filtered image.

14. The system as claimed in claim 13, wherein said first analysis circuit and said first synthesizer form a quadrature mirror pair.

15. The system as claimed in claim 13, wherein said second analysis circuit and said second synthesizer form a quadrature mirror pair.

16. The system as claimed in claim 14, wherein said second analysis circuit and said second synthesizer form a quadrature mirror pair.

17. The system as claimed in claim 13, further comprising:

a sigma circuit, operatively connected to said first, second, and third sigma filter circuits, to determine a sigma value from the image.

18. The system as claimed in claim 17, wherein said sigma circuit comprises:

a high pass filter circuit to high pass filter the image; and

a circuit to determine a standard deviation of the high pass filtered image, the determined standard deviation being the sigma value.

19. The system as claimed in claim 18, wherein the determined standard deviation is used as the sigma value when the determined standard deviation is less than a predetermined value.

20. The system as claimed in claim 13, further comprising:

a fourth sigma filter to sigma filter the first reconstructed image to produce a sigma filtered first reconstructed image;

said second synthesizer synthesizing the sigma filtered first reconstructed image and the first detail part to produce a final filtered image.