Television – Bandwidth reduction system – Data rate reduction
Reexamination Certificate
1998-10-22
2002-12-03
Rao, Andy (Department: 2713)
Television
Bandwidth reduction system
Data rate reduction
C375S240160
Reexamination Certificate
active
06489995
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to recovery of motion vectors from damaged encoded data.
2. Art Background
In predictive video coding techniques, such as MPEG (Motion Picture Experts Group) or ITU/T H.26 x code, each video frame is divided into macro-blocks of regular size. To achieve compression, the macro-blocks are predicted from the previous frames, and motion information in the form of motion vectors and the prediction residual are transmitted to the decoder in place of transmitting the pixel values directly. To achieve a high compression ratio, a variable-length coding scheme, such as Huffman coding, is applied to the motion vector to increase the compression efficiency of the video system. However, when a transmission error occur, it often causes lost of synchronization, and hence results in error propagation. As a result, all codewords after the noise corrupted codeword and before the next synchronization word are also corrupted which results in non-reliable communications. Even a single bit-error may cause the decoder to continually produce erroneously decoded data due to the property of variable-length codes. This effectively increases the Bit Error Rate (BER) and lowers the Quality of Service (QOS) of a system where the signals are easily corrupted by burst transmission errors.
The number of motion vectors lost due to noise corruption can be reduced by increasing the frequency of the synchronization words in the data stream or by the application of reversible variable length codes. However, noise corruption will still cause errors in macro-blocks and hence the motion vectors may not be available in the decoder.
Motion vector concealment or temporal error concealment refers to a process to recover the motion vectors lost due to noise corruption during transmission. Most techniques in literature are concentrated in two categories: unshifted replacement and shifted replacement. In unshifted replacement, a lost macro-block is replaced by the macro-block in the preceding picture at exactly the same location. A drawback of unshifted replacement is that it leads to annoying motion blocking artifacts in active regions in a moving picture. In shifted replacements, a new motion vector is generated from neighboring macro-block's motion vectors by techniques, such as averaging, median etc., to recover or conceal the noise corrupted macro-block. There are several drawbacks to shifted replacement. The neighboring macro-blocks may not have motion vector information, e.g., neighboring macro-blocks can be intra-coded, or the neighboring blocks are also noise corrupted. In addition, the motion field generated by the neighboring block's motion vector may not be smooth. A smooth motion field is required to minimize both motion blocking and static blocking artifacts in the decoded images. Hence, the simple motion vector regeneration algorithms used in shifted replacement will not be able to generate a human perception pleasing motion vector to conceal the noise corrupted macro-blocks.
SUMMARY OF THE INVENTION
A method and apparatus of the present invention decodes an encoded portion of an image having an error in one of its parameters, such as a motion vector, by estimating the parameter using neighboring block information. In particular in one embodiment, sub-portions from neighboring decoded portions of an image are extracted. A motion vector is then generated for each sub-portion. In one embodiment, the motion field generated by the motion vectors of each sub-portion is made smooth by using sub-portions that have overlapping regions. Using the motion vectors generated for each sub-portion, a motion vector is estimated for the encoded portion. This estimated motion vector is then used to decode the encoded portion of an image such as the video frame.
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Kok Chi Wah
Lu Ning
Blakely , Sokoloff, Taylor & Zafman LLP
Rao Andy
Sony Corporation
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