Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Patent
1998-02-04
2000-09-26
Le, Vu
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
3484201, 3484211, H04N 712
Patent
active
061251461
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method of coding digital video data corresponding to the pixels of a sequence of pictures, comprising at least a block forming step, for dividing the input video data into blocks, a quantization and coding step, for quantizing data corresponding to each block and coding the quantized data, and a control step, for controlling a quantization parameter of said quantization and coding step in accordance with another parameter that depends on the content of each block.
The invention also relates, for the implementation of this method, to a system for coding digital video data corresponding to the pixels of a sequence of pictures, comprising at least a block converter, for dividing the input video data associated to one picture into blocks, a quantization and coding sub-assembly, for quantizing data corresponding to each block and coding the quantized data, and a control sub-assembly, for controlling a quantization parameter of said quantization and coding sub-assembly in accordance with a parameter that depends on the content of each block.
Such an invention may be used in the field of digital television, especially according to the MPEG standard (described for instance in the document "MPEG: a video compression standard for multimedia applications", D. Le Gall, Communications of the ACM, April 1991, vol.34, n.sup.o 4, pp.46-58) and, more generally, is of interest in the field of multimedia applications.
BACKGROUND OF THE INVENTION
Most of MPEG decoders usually comprise an external memory of 16,8 Mbits (1 Mbit=2.sup.20 bits), or even more when they have to support decoding at main level/main profile. It is known for instance that the incoming bitstream has to be stored in an input buffer (VBV-buffer), the theoretical capacity of which is equal to 1,835 Mbit. However, since a practical decoder cannot decode instantaneously, some additional buffer is required, which increases the input buffer to a capacity of about 2,5 Mbits. Moreover, in order to support a bidirectional motion compensation, the decoder must include two reference frames. The storage capacity for one reference frame is 5 Mbits for 50 Hz systems and 4,1 Mbits for 60 Hz systems. To enable the decoding of both standards, 10 Mbits have therefore to be provided in the decoder for the storage of both reference frames. It must also be recalled that the reconstruction of MPEG video signals after decoding occurs in a macroblock order whereas the information to be displayed is required in an interlaced scanning line format. As the macroblocks are frame coded, the information of both fields has to be delivered during decoding, and the conversion from the frame coded macroblock format to the interlaced scanning line format requires a conversion memory, generally of 5 Mbits or 4,1 Mbits according to the system (50 Hz or 60 Hz). The total memory requirement then becomes equal to (2,5+(3.times.4,1))=14,8 Mbits for a 60 Hz decoder and to (2,5+(3.times.5))=17,5 Mbits for a 50 Hz decoder. For this last one, the practical 16 Mbits limit is therefore exceeded.
Moreover, the integrated circuit technology that is to-day available allows to implement other functionalities than video decoding, for example combinations with audio decoding and bidimensional graphics, and next generation MPEG decoders will probably include demultiplexing functions and improved processors. All these additional functions are memory demanding and their performance is determined by the amount of available memory capacity.
In order to solve this problem, it has been added extra memory (of 4 Mbits) to the MPEG decoder, but such a solution is provisional and will be probably obsolete in a near future. More expensive 16 Mbits memories will then be added.
Another proposed solution, described in the document EP 0618722, has consisted in reducing the memory capacity for display conversion. By using the display memory in a macroblock line fashion rather than on field basis, the capacity of the display memory has been reduced from 5 Mbits to
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De With Peter
Frencken Peter
Le Vu
U.S. Philips Corporation
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