Method and apparatus for blocking effect reduction in images

• US 5,974,196 A
• Filed: 03/15/1996
• Issued: 10/26/1999
• Est. Priority Date: 03/15/1996
• Status: Expired due to Fees

• Current Assignee: Sony Corporation (Sony Group Corp.), Sony Electronics Inc. (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.), Sony Electronics Inc. (Sony Group Corp.)
• Inventors: Lee, Chuen-Chien, Chang, Ching-Fang
• Primary Examiner(s): Lee, Thomas D
• Application Number:
  US08/616,559
• Time in Patent Office: 1,320 Days
• Field of Search: 382/268, 382/266, 382/269, 382/254, 382/248, 382/250, 382/251, 358/432, 358/433
• US Class Current: 382/268
• 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 19/182 the unit being a pixel
• CPC Class Codes: H04N 19/86 involving reduction of coding artifacts, e.g. of blockiness

Abstract

An apparatus and method for post processing image data which previously was encoded using a discrete cosine transform in order to remove resulting blocking effects. Possible blocking points are examined to determine whether blocking points exist. If blocking points are determined, an adjustment value for each blocking point is computed and proportionately utilized to adjust the adjacent and neighboring pixels.

Claims

1. A method for minimizing blocking effects in a blocking image caused by prior performance of a discrete cosine transform (DCT) and quantization process, said blocking image described by blocking image data comprising blocks of pixel data, said method comprising the steps of:

determining whether at least one blocking point occurs respectively at boundary points of a block based upon a pre-specified range of values indicative of a blocking point;

if at least one blocking point is identified; and

for each blocking point identified;

determining an adjustment value based upon a blocking step and local variance; and

adjusting blocking data corresponding to pixel locations adjacent to the blocking point and neighboring pixels to the adjacent pixels.

2. The method as set forth in claim 1, wherein boundary points comprise vertical boundary points and horizontal boundary points and the step of determining whether at least one blocking point occurs comprises the steps of:

for each vertical boundary point examined;

generating the difference between pixel data between pixels horizontally adjacent to the vertical boundary point,

comparing the difference to the pre-specified range of values indicative of a blocking point, and

identifying a blocking point if the difference is within the pre-specified range of values; and

for each horizontal boundary point examined;

generating the difference between pixel data between pixels vertically adjacent to the horizontal boundary point,

comparing the difference to the pre-specified range of values, and

identifying a blocking point if the difference is within the pre-specified range of values.

3. The method as set forth in claim 1, wherein the pre-specified range of values indicative of a blocking point comprises an upper and lower limit, said upper and lower limits selected such that normal minor image variation between pixels are not detected as blocking points and significant image variations are not detected as blocking points.

4. The method as set forth in claim 1, wherein the pre-specified range of values indicative of a blocking point comprises an upper limit and lower limit, said lower limit comprising the local variance of neighborhood pixels to the blocking point.

5. The method as set forth in claim 4, wherein the local variance of neighborhood pixels is determined by averaging a summation of absolute values of a neighborhood of pixels about the blocking point.

6. The method as set forth in claim 1, wherein the pre-specified range of values indicative of a blocking point comprises an upper limit and lower limit, said upper limit comprising an empirically determined value chosen to reflect an error larger than an error that can be caused by quantization of the block during the quantization process.

7. The method as set forth in claim 1, wherein the step of determining an adjustment value comprises the step of generating the adjustment value such that the difference between pixel data of pixels adjacent to the blocking point is adjusted to a local variance of a neighborhood of pixels about the blocking point.

8. The method as set forth in claim 1, wherein the step of determining the adjustment value comprises the steps of:

if a first difference between pixel values of pixels adjacent to the blocking point is greater than zero, computing the adjustment value to be a second difference between the first difference and a local variance, wherein the local variance of neighborhood pixels is determined by averaging a summation of absolute values of a neighborhood of pixels about the blocking point; and

if the first difference is less than or equal to zero, computing the adjustment value to be a sum of the first difference and the local variance.

9. The method as set forth in claim 1, wherein the step of adjusting comprises adjusting adjacent and neighboring pixels by proportionate amounts of the adjustment value.

10. The method as set forth in claim 1, wherein the step of adjusting comprises the step of adjusting adjacent and neighboring pixels by proportionate amounts of the adjustment value proportionate to a distance each pixel of the adjacent and neighboring pixel is from the blocking point.

11. An apparatus for minimizing blocking effects in a blocking image caused by prior performance of a discrete cosine transform (DCT) and quantization process, said blocking image described by blocking image data comprising blocks of pixel data, said apparatus comprising:

an input device for receiving blocking image data;

a processor coupled to the input device, said processor comprising a central processing unit and memory, said processor determining whether at least one blocking point occurs respectively at boundary points of a block based upon a pre-specified range of values indicative of a blocking point; and

if at least one blocking point is determined, for each blocking point identified, determining an adjustment value based upon a blocking step and local variance and adjusting pixel data corresponding to pixel locations adjacent to the blocking point and neighboring pixels to the adjacent pixels.

12. The apparatus as set forth in claim 11, further comprising a display device coupled to the processor to display pixel data output by the processor.

13. The apparatus as set forth in claim 11, wherein boundary points comprise vertical boundary points and horizontal boundary points and the processor determines whether at least one blocking point occurs by examining each vertical boundary point by generating the difference between pixel data between pixels horizontally adjacent to the vertical boundary point, comparing the difference to the pre-specified range of values indicative of a blocking point, and identifying a blocking point if the difference is within the pre-specified range of values;

and examining each horizontal boundary point and generating the difference between pixel data between pixels vertically adjacent to the horizontal boundary point, comparing the difference to the pre-specified range of values, and identifying a blocking point if the difference is within the pre-specified range of values.

14. The apparatus as set forth in claim 11, wherein the pre-specified range of values indicative of a blocking point comprises an upper and lower limit, said upper and lower limits selected such that normal minor image variation between pixels are not detected as blocking points and significant image variations are not detected as blocking points.

15. The apparatus as set forth in claim 11, wherein the pre-specified range of values indicative of a blocking point comprises an upper limit and lower limit, said lower limit comprising the local variance of neighborhood pixels to the blocking point.

16. The apparatus as set forth in claim 15, wherein said processor determines the local variance of neighborhood pixels by averaging a summation of absolute values of a neighborhood of pixels about the blocking point.

17. The apparatus as set forth in claim 11, wherein the pre-specified range of values indicative of a blocking point comprises an upper limit and lower limit, said upper limit comprising an empirically determined value chosen to reflect an error larger than an error that can be caused by quantization of the block during the quantization process.

18. The apparatus as set forth in claim 11, wherein the processor determines the adjustment value such that the difference between pixel data of pixels adjacent to the blocking point is adjusted to a local variance of a neighborhood of pixels about the blocking point.

19. The apparatus as set forth in claim 11, wherein the processor determines the adjustment value to be a second difference between the first difference and a local variance if a first difference between pixel values of pixels adjacent to the blocking point is greater than zero, and determines the adjustment value to be a sum of the first difference and the local variance if the first difference is less than or equal to zero, wherein the local variance of neighborhood pixels is determined by averaging a summation of absolute values of a neighborhood of pixels about the blocking point.

20. The apparatus as set forth in claim 11, wherein the processor adjusts adjacent and neighboring pixels by proportionate amounts of the adjustment value.

21. The apparatus as set forth in claim 11, wherein the processor adjusts adjacent and neighboring pixels by proportionate amounts of the adjustment value proportionate to a distance each pixel of the adjacent and neighboring pixel is from the blocking point.