Television – Bandwidth reduction system – Data rate reduction
Patent
1992-12-03
1996-01-30
Britton, Howard W.
Television
Bandwidth reduction system
Data rate reduction
348403, 348420, 348423, H04N 730, H04N 764
Patent
active
054884187
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to an encoder for encoding a video signal used in a television system or the like, and to a decoder for decoding encoded data which is recorded on a recording medium.
DESCRIPTION OF RELATED ART
When a video signal of a dynamic image such as a television signal is transmitted at a low bit rate, discrete cosine transformation (DCT) is generally used. For example, the DCT is employed in the draft recommendation of September, 1990 in MPEG (Moving Picture Experts Group) of the International Standards Organization (abbreviated as ISO). The MPEG further intends to use Huffman coding, which is a kind of the variable-length encoding, so that information to be transmitted is compressed by a combination of the DCT and the variable-length encoding.
In this variable-length encoding method, however, when an error occurs once, the error may propagate over blocks of the DCT. Since error-correcting codes are generally added, such an error will not undoubtedly occur. However, in a transmission channel such as in a digital VTR in which first errors occur relatively frequently, for example, burst errors can occur in a degree exceeding the error correction capability. In such a case, there arises a problem in that the error propagation spreads over the blocks. An example of such a case will be described below.
FIGS. 1(A) and 1(B) are block diagrams illustrating the configuration of a conventional encoder and decoder. The encoder has a DCT circuit 101 which performs the DCT on each block, a quantizer 102 which quantizes transformed coefficients from the DCT circuit 101, and a Huffman encoding circuit 103 which performs the Huffman encoding on the output of the quantizer 102. The decoder comprises a Huffman decoding circuit 104 which performs the Huffman decoding on input data, an inverse quantizer 105 which performs the inverse quantization on the output of the Huffman decoding circuit 104, and an inverse DCT circuit 106-which performs the inverse DCT on the output of the inverse quantizer 105.
The operation will be specifically described. It is assumed that, for example, results obtained by the blocking of 8.times.8 pixels and the transform in the DCT circuit 101 are arranged as shown in FIG. 2. The results are subjected to the run-length encoding by scanning them in a zig-zag manner as shown in FIG. 3. In a case of a specific example of data shown in FIG. 4, for example, these data are transformed by the run-length encoding into the data shown in the left side of FIG. 5. When subjected to the Huffman encoding using the Huffman encoding table shown in FIG. 6, these are transformed into codes having various code lengths as shown in the right side of FIG. 5. In general, after the blocking process, added is a data which is called EOB (End of Block) and indicates the end of a block.
Next, the manner of performing a decoding operation in a case will be described, for example, wherein a 1-bit error Occurs in the data of 10111010 having the run-length (length of consecutive 0-values) of 0 and the value (the value of non-zero) of 16, with the result that the data becomes 11111010. At first, it is assumed that the data preceding this data have been normally decoded, and therefore it is not necessary to consider these preceding data. According to the Huffman encoding table shown in FIG. 6, the data of 11111010 is broken down into 11, 11 and 1010. Since 11 has the run-length of 0 and the value of 1, it becomes different from the original data. Furthermore, since the data of 1010 does not exist in the Huffman encoding table, numerals from the next data of 101110111 are added in sequence to 1010, and then the decoding is performed. As a result, the first 10101 in 1010101110111 is decoded to the run-length of 0 and the value of 5 according to the Huffman encoding table of FIG. 6.
In 01110111 which remains as a result of removing 10101, 01110 is decoded to the run-length of 0 and the value of 7 according to FIG. 6. In the remaining 111, the first 11 is decoded to the run-length of 0 and the v
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patent: 5036391 (1991-07-01), Auvray
patent: 5218622 (1993-06-01), Fazel et al.
patent: 5239308 (1993-08-01), Keesen
"Information technology--Coding of moving pictures and associated audio for digital storage media at up to about 1,5 Mbit/s"Part 2: Video; International Standard; ISO/IEC 11172-2; 1993; pp. 1-38.
Nikkei Electronics; Oct. 15, 1990; Unix; pp. 116-147.
"A Consideration on Filters in the Coding Loop of Hybrid MC/DCT Coding Scheme"; IE86-100, 2-26-87; pp. 17-23.
IEEE Transactions on Information Theory, vol. IT-22, No. 4, Jul. 1976.
Paper entitled "Criteria for the Protection of the Video Information in a Codec Based on DCT"; Signal Processing of HDTV, II; Proceedings of the Third International Workshop on HDTV, Turin, ITaly (Aug. 30, 1989-Sep. 1, 1989); pp. 769-776.
Itow Takashi
Mishima Hidetoshi
Britton Howard W.
Mitsubishi Denki & Kabushiki Kaisha
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