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 correction mode using information from the first block and information from the second block, wherein the correction mode is selected from at least two correction modes;
selecting a quantity of pixels to be adjusted based on the selected correction mode; 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 a first correction mode is selected; and
selecting at least six pixels to be adjusted if a second correction mode is selected.
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 a first correction mode is selected; and
selecting no more than six pixels to be adjusted if a second correction mode is selected.
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 a first correction mode is selected; and
selecting exactly six pixels to be adjusted if a second correction mode is selected.
5. The method of claim 4 , wherein selecting the two pixels to be adjusted if the first correction mode is selected 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 second correction mode is selected 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 a first correction mode is selected than if a second correction mode is selected.
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 correction mode using information from the first block and information from the second block, wherein the correction mode is selected from at least two correction modes,
select a quantity of pixels to be adjusted based on the selected correction mode, and
adjust the selected quantity of pixels.