Methods and apparatus to reduce blocking noise and contouring effect in motion compensated compressed video

Abstract

Methods and systems are disclosed for removing artifacts, such as blocking noise and contouring effects, from a block-encoded video signal. One method for removing blocking artifacts involves decoding the block-encoded signal to obtain a decoded sequence of video frames and one or more associated motion vectors. By using the motion vector, the location of one or more blocking artifacts may be identified within at least one of the frames. The location identified by the motion vector is filtered to remove at least some of the blocking artifacts. Another method for removing contouring effects involves decoding the block-encoded signal to obtain a decoded sequence of video frames, detecting a contouring effect by evaluating the macroblock mode and DCT coefficient information from the decoded signal, and filtering one or more blocks correlating to the detected contouring effect.

1 - 34 . (canceled) 
     
     
         35 . A method for decoding a block-encoded video signal, the video signal having contouring effects from the encoding process, the method comprising:
 decoding the block-encoded signal to obtain a decoded sequence of video frames, each of the video frames comprising a plurality of macroblocks having macroblock mode information and DCT coefficient information;   detecting a contouring effect by evaluating the macroblock mode and DCT coefficient information; and   filtering one or more blocks correlating to the detected contouring effect.   
     
     
         36 . A method as in  claim 35 , wherein the contouring effect forms a boundary between first and second adjacent blocks, each block comprising an array of pixels, and wherein detecting a contouring effect comprises determining whether each block is an intra-coded block or an inter-coded block, wherein the boundary is considered for further evaluation as a contouring effect candidate if both the first and second blocks are found to be intra-coded blocks. 
     
     
         37 . A method as in  claim 36 , wherein detecting a contouring effect further comprises evaluating the DCT coefficient information associated with the first and second blocks, the DCT coefficient information comprising AC and DC coefficients, wherein the boundary is considered for further evaluation as a contouring effect candidate if the only non-zero coefficient in both of the first and second blocks is the DC coefficient. 
     
     
         38 . A method as in  claim 37 , wherein detecting a contouring effect further comprises evaluating whether a boundary comprises an actual image edge or an artificial image edge, and wherein the boundary is considered a contouring effect if the boundary is found to be an artificial image edge. 
     
     
         39 . A method as in  claim 38 , wherein determining whether the boundary is an artificial edge comprises evaluating the pixels bordering both sides of the boundary, wherein the boundary is considered a contouring effect if the difference in the pixels fall below a threshold value. 
     
     
         40 . A method as in  claim 39 , wherein a quantization parameter is obtained from the decoded video signal, and wherein the boundary is considered a contouring effect if the absolute value of the pixel difference on both sides of the discontinuity is less than two times the quantization parameter. 
     
     
         41 . A method as in  claim 36 , wherein filtering one or more blocks comprises applying a uniform low-pass filter. 
     
     
         42 . A method as in  claim 41 , wherein the method further comprises determining the size of the filter by comparing adjacent blocks on a first side of the boundary. 
     
     
         43 . A method as in  claim 42 , further comprising comparing adjacent blocks on a second side of the boundary opposite from the first side. 
     
     
         44 . A method as any one of  claims 41  and  42 , wherein the comparing adjacent blocks comprises totaling the number of consecutive similar blocks away from the boundary. 
     
     
         45 . A method as in  claim 44 , wherein a block is considered similar if the value of the pixel adjacent the block boundary of the first block is the same as the value of the first two pixels adjacent the boundary in the second block. 
     
     
         46 . A method as in  claim 44 , wherein the size of the filter is equal to the lesser of the similar block totals on either side of the boundary multiplied by the number of pixels in one row of a block. 
     
     
         47 . A system for decoding a block-encoded video signal, the video signal having contouring effects from the encoding process, the system comprising:
 a first processing element adapted to decode the block-encoded signal to obtain a decoded sequence of video frames, each of the video frames comprising a plurality of macroblocks having macroblock mode information and DCT coefficient information;   a second processing element adapted to detect a contouring effect by evaluating the macroblock mode and DCT coefficient information; and   a filter for filtering one or more blocks correlated to the detected contouring effect.   
     
     
         48 . A system as in  claim 47 , wherein the filter comprises a low-pass filter. 
     
     
         49 . A system as in  claim 48 , wherein the filter comprises a uniform low-pass filter. 
     
     
         50 . A system as in  claim 48 , wherein the contouring effect forms a boundary between first and second adjacent blocks, and wherein the size of the filter is determined by the number of similar blocks on one side of the boundary. 
     
     
         51 . A method for removing contouring effect from a block-encoded video signal, the decoded signal comprising sequence of video frames, each of the video frames comprising a plurality of macroblocks having macroblock mode information and DCT coefficient information, the method comprising:
 collecting the macroblock mode information and DCT coefficient information;   detecting a contouring effect by evaluating the macroblock mode and DCT coefficient information; and   filtering one or more blocks correlating to the detected contouring effect.   
     
     
         52 . A method as in  claim 51 , wherein the contouring effect forms a boundary between first and second adjacent blocks, each block comprising an array of pixels. 
     
     
         53 . A method as in  claim 52 , and wherein detecting a contouring effect comprises determining whether each block is an intra-coded block or an inter-coded block, wherein the boundary is considered for further evaluation as a contouring effect candidate if both the first and second blocks are found to be intra-coded blocks. 
     
     
         54 . A method as in  claim 53 , wherein detecting a contouring effect further comprises evaluating the DCT coefficient information associated with the first and second blocks, the DCT coefficient information comprising AC and DC coefficients, wherein the boundary is considered for further evaluation as a contouring effect candidate if the only non-zero coefficient in both of the first and second blocks is the DC coefficient. 
     
     
         55 . A method as in  claim 54 , wherein detecting a contouring effect further comprises evaluating whether a boundary comprises an actual image edge or an artificial image edge, and wherein the boundary is considered a contouring effect if the boundary is found to be an artificial image edge. 
     
     
         56 . A method as in  claim 51 , wherein filtering one or more blocks comprises applying a uniform low-pass filter. 
     
     
         57 . A method as in  claim 56 , wherein the contouring effect forms a boundary between first and second adjacent blocks, each block comprising an array of pixels, and wherein the method further comprises determining the size of the filter by comparing adjacent blocks on a first side of the boundary.