Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Patent
1998-11-13
2000-09-19
Kelley, Chris S.
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
708631, 708107, 382107, 382241, 382238, H04N 5262
Patent
active
061223204
DESCRIPTION:
BRIEF SUMMARY
The invention described herein relates to digitised video signal processing, and in particular it concerns a circuit for motion estimation in encoding or compressing digitised video sequences. Hereinafter, reference will be made, by way of non-limiting example, to sequences conforming to international standard ISO/IEC 13818-2 (also known as ISO/MPEG2), but the invention can be applied to sequences encoded and decoded according to principles similar to those disclosed in the standard. For the sake of simplicity, those sequences shall hereinafter be referred to as MPEG2 video sequences or data.
As is well known, the standard specifies the encoded (or compressed) representation of video sequences for digital storage and digital video communications and defines the decoding process. The encoding process is not defined in the standard, and it is essentially a hybrid coding, using time prediction techniques with motion estimation (at the level of a pixel aggregate corresponding to one of the hierarchical levels defined by the standards, e.g. macro-block level) to reduce time redundancy, and two-dimensional transform techniques applied to a current picture or to the significant differences between the current picture and a predicted picture to reduce spatial redundancy. Information on the encoding procedures (e.g. with or without prediction and/or motion compensation), motion information and spatial information are then included into the sequence, which is transmitted or stored after encoding with a variable length code. Decoding entails processing the compressed sequences in successive steps, until recovering the original picture sequence, for its subsequent display. Greater detail can be found in the standard mentioned above as well as in standard ISO/IEC 11172-2 (ISO/MPEG1) and in the paper `The MPEG video compression algorithm`, by D. J. Le Gall, Signal Processing: Picture Communication, Vol. 4, No. 2, pp. 129 et seq.
Motion information generally includes one or more vectors (the number of which depends on the type of picture and on the type of prediction requested) representing a displacement of a luminance macro-block (16.times.16 pixels) in a current picture with respect to the position the macro-block has in one or more reference pictures, and a `cost` function which provides an indication of the estimation error. A reference picture is a picture which was subjected to intra-picture encoding (I picture), i. e. a picture encoded by exploiting only the information contained in the picture itself, or a picture encoded with prediction (P picture), i. e. a picture for which the difference is encoded between the current picture and a picture obtained by means of a prediction with motion compensation starting from one or more past reference pictures. The vector(s) supplied by the motion estimation units is (are) the vector(s) which minimise(s) the cost function, i. e. motion estimation identifies the macro-block(s) that, in the reference picture(s), best match(es) the current macro-block. The motion information may also be used as a parameter for evaluating a coding cost function, to allow the application of the prediction strategy that results in the best trade-off between coding quality and amount of information to be transmitted.
The matching criteria (or cost functions) most commonly adopted in motion estimation are the mean absolute or mean square difference (or error) between the luminance pixels in the macro-block in the current picture and homologous pixels in macro-blocks within a search area in the reference picture. Theoretically, in order that the best matching macro-block is actually identified, all possible macro-block positions within the search area should be considered (full search) and, moreover, the search area should be relatively large to ensure a reliable estimation. Taking into account that a macro-block contains 256 pixels and that a number of vector/cost pairs are to be computed for each macro-block, it is clear that the computational burden inherent in motion estimation is very severe,
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Bursky D: "CODEC Compresses Images In Real Time" Electronic Design, vol. 41, No. 20, pp. 123/124, Oct. 1993.
Bennetts et al: "IEEE Standard 1149.1-1990 on Boundary Scan: History, Literature Survey, and Current Status" Journal of Electronic Testing, vol. 2, No. 1, pp. 11-25, Mar. 1999.
Bellifemine Fabio
Bollano Gianmario
Dogimont Stephanie
Finotello Andrea
Gandini Marco
An Shawn S.
Cselt-Centro Studi e Laboratori Telecomunicazioni S.p.A.
Dubno Herbert
Kelley Chris S.
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