Method of reducing a blocking artifact when coding moving picture
View Patent ↗A method of coding a moving picture is provided that reduces blocking artifacts. The method can include defining a plurality of defining pixels S 0 , S 1 , and S 2 , which are centered around a block boundary. If a default mode is selected then frequency information of the surroundings of the block boundary is obtained. A magnitude of a discontinuous component in a frequency domain belonging to the block boundary is adjusted based on a magnitude of a corresponding discontinuous component selected from a pixel contained entirely within a block adjacent the block boundary. The frequency domain adjustment is then applied to a spatial domain. Or, a DC offset mode can be selected to reduce blocking artifacts in smooth regions where there is little motion.
1. A method of reducing a blocking artifact appearing when coding a picture, comprising:
dividing the picture into blocks that each include multiple pixels, a first pixel of a first block being separated from a second pixel of a neighboring second block by a block boundary;
selecting a correction mode from at least a default mode and a direct current (DC) offset mode based on whether a region adjacent to the block boundary is smooth; and
adjusting the first pixel of the first block based upon the second pixel of the second block when the default mode is selected.
2. The method of claim 1 ,
wherein adjusting the first pixel further comprises replacing a pixel value v 3 of the first pixel with a value v 3 ′,
wherein the value v 3 ′ is expressed as:
v 3 ′=v 3 −d,
wherein d is expressed as:
d
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wherein α 3,0 ′ is expressed as:
α 3,0 ′=SIGN(α 3,0 )*MIN(|α 3,0 |,|α 3,1 |,|α 3,2 |),
wherein QP represents a quantization parameter of the second block, c 2 and c 3 represent DCT kernel coefficients, and v 4 represents a pixel value of the second pixel.
3. The method of claim 2 , wherein if, and wherein
δ(|α 3,0 |<QP )=0 |α 3,0 |≧QP δ (|α 3,0 |<QP )=1 if |α 3,0 |<QP.
4. The method of claim 2 , wherein c 2 is an integer and c 3 is a multiple of 2.
5. The method of claim 4 , wherein c 2 =5 and c 3 =8.
6. The method of claim 1 , further comprising applying the adjusting operation to a spatial domain of the first pixel.
7. The method of claim 1 , wherein the block boundary is a vertical or horizontal block boundary.
8. The method of claim 1 , further comprising adjusting the second pixel based upon frequency information of the first pixel when the default mode is selected.
9. The method of claim 1 , wherein a magnitude of the adjusting operation is constrained to be no greater than half of the difference between a value of the first pixel and a value of the second pixel, using a clipping function.
10. The method of claim 1 , wherein a magnitude of the adjusting operation is based upon a simple inner product of a DCT kernel and the first and second pixels.
11. The method of claim 1 , wherein a magnitude of the adjusting operation is based upon a minimum magnitude of frequency information of the first and second pixels.
12. The method of claim 1 , wherein a magnitude of the adjusting operation is based upon frequency information of the first pixel and the second pixel when the default mode is selected.
13. The method of claim 1 , further comprising obtaining the frequency information for the second pixel, wherein the first pixel is adjusted if a magnitude of the blocking artifact is less than a quantization parameter of the second block.
14. The method of claim 1 , wherein the first pixel is adjusted in a first way when the default mode is selected, the method further comprising modifying the first pixel in a second, different way when the DC offset mode is selected.
15. The method of claim 1 ,
wherein the default mode is selected if the region adjacent to the block boundary is smooth, and
wherein the DC offset mode is selected if the region adjacent to the block boundary is not smooth.
16. An apparatus for reducing a blocking artifact appearing when coding a picture, the apparatus comprising a blocking filter configured to:
divide the picture into blocks that each include multiple pixels, a first pixel of a first block being separated from a second pixel of a neighboring second block by a block boundary;
select a correction mode from at least a default mode and a direct current (DC) offset mode based on whether a region adjacent to the block boundary is smooth; and
adjust the first pixel of the first block based upon the second pixel of the second block when the default mode is selected.
17. An apparatus for reducing a blocking artifact appearing when coding a picture, comprising:
means for dividing the picture into blocks that each include multiple pixels, a first pixel of a first block being separated from a second pixel of a neighboring second block by a block boundary;
means for selecting a correction mode from at least a default mode and a direct current (DC) offset mode based on whether a region adjacent to the block boundary is smooth; and
means for adjusting the first pixel of the first block based upon the second pixel of the second block when the default mode is selected.