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, wherein the pixels of a first block are separated from pixels of a neighboring second block by a block boundary;
selecting a quantity of pixels to be adjusted based on whether a region adjacent to the block boundary is smooth; and
adjusting the selected quantity of pixels.
2. The method of claim 1 , wherein selecting the quantity of pixels to be adjusted further comprises:
selecting at least two pixels to be adjusted if the region adjacent to the block boundary is not smooth; and
selecting at least six pixels to be adjusted if the region adjacent to the block boundary is smooth.
3. The method of claim 1 , wherein selecting the quantity of pixels to be adjusted further comprises:
selecting no more than two pixels to be adjusted if the region adjacent to the block boundary is not smooth; and
selecting no more than six pixels to be adjusted if the region adjacent to the block boundary is smooth.
4. The method of claim 1 , wherein selecting the quantity of pixels to be adjusted further comprises:
selecting exactly two pixels to be adjusted if the region adjacent to the block boundary is not smooth; and
selecting exactly six pixels to be adjusted if the region adjacent to the block boundary is smooth.
5. The method of claim 4 , wherein selecting the two pixels to be adjusted if the region adjacent to the block boundary is not smooth further comprises:
selecting one pixel from the first block to be adjusted; and
selecting one pixel from the second block to be adjusted.
6. The method of claim 4 , wherein selecting the six pixels to be adjusted if the region adjacent to the block boundary is not smooth further comprises:
selecting three pixels from the first block to be adjusted; and
selecting three pixels from the second block to be adjusted.
7. The method of claim 1 , wherein fewer pixels are selected to be adjusted if the region adjacent to the block boundary is not smooth, than if the region adjacent to the block boundary is smooth.
8. The method of claim 1 , further comprising applying the adjusting operation to a spatial domain of the selected quantity of pixels.
9. The method of claim 1 , wherein the block boundary is a vertical or horizontal block boundary.
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 selected quantity of 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 selected quantity of pixels.
12. The method of claim 1 , wherein a magnitude of the adjusting operation is based upon frequency information of the selected quantity of pixels.
13. The method of claim 1 ,
wherein adjusting the selected quantity of pixels further comprises replacing a pixel value v 3 of a 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:
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wherein a 3,0 ′ is expressed as:
a 3,0 ′=SIGN( a 3,0 )*MIN(| a 3,0 |,|a 3,1 |,|a 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 a neighboring second pixel.
14. The method of claim 13 , wherein δ(|a 3,0 |<QP)=1 if |a 3,0 |<QP, and wherein δ(|a 3,0 |<QP)=0 if |a 3,0 |≧QP.
15. The method of claim 13 , wherein c 2 is an integer and c 3 is a multiple of 2.
16. The method of claim 15 , wherein c 2 =5 and c 3 =8.
17. The method of claim 13 , further comprising adjusting the neighboring second pixel based upon frequency information of the first pixel.
18. The method of claim 13 , 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.
19. The method of claim 13 , further comprising obtaining the frequency information for the neighboring 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.
20. 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, wherein the pixels of a first block are separated from pixels of a neighboring second block by a block boundary,
select a quantity of pixels to be adjusted based on whether a region adjacent to the block boundary is smooth, and
adjust the selected quantity of pixels.