Pulse or digital communications – Bandwidth reduction or expansion
Reexamination Certificate
1997-12-22
2001-08-21
Le, Vu (Department: 2713)
Pulse or digital communications
Bandwidth reduction or expansion
C348S409100, C348S415100
Reexamination Certificate
active
06278734
ABSTRACT:
BACKGROUND OF THE INVENTION
Method for decoding and coding a compressed video data stream with a reduced memory requirement
The present standards for compressing video data, MPEG
1
and MPEG
2
, operate in accordance with the principles of prediction and transformation. A distinction is made between three differently coded types of pictures. So-called I pictures (intra-coded pictures) are only transform-coded. The transform used is the discrete cosine transform (DCT). P pictures are predicted from the respectively preceding I picture or P picture. The difference between the predicted picture and the actual picture is DCT-transformed. The third type of pictures are the so-called B pictures, which are bidirectionally predicted from the respectively preceding I picture or P picture and from the respectively succeeding I picture or P picture. The difference between the predicted picture and the actual picture is again DCT-transformed.
An MPEG decoder must therefore make available the data of two pictures (I picture and P picture) for the reconstruction of the B pictures. Accordingly, the memory requirement for pictures is high.
The fundamental mode of operation of the compression methods MPEG
1
and MPEG
2
has been disclosed to the person skilled in the art by various publications (D. J. Le Gall, The MPEG Video Compression Algorithm, Signal Processing: Image Communication 4, pp. 129-140, 1992; International Standard ISO/IEC 11172-2: Coding of Moving Pictures and Associated Audio, ISO/MPEG, 1993 and Draft International Standard ISO/IEC 13818-2, Generic Coding of Moving Pictures and Associated Audio, 25.3.1994, 1994).
In order to improve the quality of the prediction in those picture areas in which moving objects occur, use is made of so-called motion-compensated prediction. The principles of the motion estimation required for this purpose and their application for the motion-compensated prediction have been disclosed to the person skilled in the art, for example by (M. Bierling, Displacement estimation by hierarchical block matching, 3rd SPIE Symp. on Visual Communications, Cambridge, Mass., November 1988, 1988) and (Draft International Standard ISO/ICE 13818-2, Generic Coding of Moving Pictures and Associated Audio, 25.3.1994, 1994).
A distinction is made between three differently coded types of pictures. So-called I pictures are transmitted without any chronological prediction, but rather are subjected only to intra-picture coding, preferably DCT coding with subsequent quantization of the coding transform coefficients. In the context of this patent application, “intra-picture coding” is to be understood quite generally as any method which is suitable for treating local correlations in video data. The so-called P pictures are predicted with the aid of the DPCM loop from chronologically preceding I pictures or P pictures (forward prediction). The difference between the predicted picture and the actual picture is subjected to intra-picture coding, preferably to transformation using a DCT with subsequent quantization of the coding transform coefficients. So-called B pictures, which are also designated as interpolated pictures in the context of the present patent application, are chronologically situated between an I picture and a P picture or between two P pictures. B pictures are determined by means of (bidirectional) motion-compensated interpolation from a chronologically preceding I picture or P picture and from a chronologically succeeding I picture or P picture. In this case, the expressions (chronologically) “succeeding” and “preceding” do not refer to the order in which these pictures are transmitted in the video data stream of the compressed pictures, but rather they refer to the order in which these pictures are recorded/reproduced. In the same way as P pictures, B pictures, too, are coded in the form of quantized coding transform coefficients of a difference picture.
In the case of currently known implementations, the reconstruction of a B picture by means of motion-compensated interpolation from a chronologically preceding I picture or P picture and from a chronologically succeeding I picture or P picture necessitates the provision of the two reference pictures (which are also occasionally designated as support pictures in the literature) in fully decoded form.
Therefore, two fully decoded reference pictures (I pictures or P pictures) have to be stored in a frame store in the case of the methods belonging to the prior art for carrying out motion-compensated interpolation.
The re-interlacing during the video output requires further storage capacity. The overall required memory is a decisive cost factor in the hardware used for decoding and encoding. A reduction in the storage capacity required is therefore desirable.
SUMMARY OF THE INVENTION
The invention is based on the problem of specifying a method for decoding compressed video data with a reduced memory requirement.
In general terms the present invention is a method for the iterative decoding of compressed video data streams which have a sequence of basic pictures and interpolated pictures. A first basic picture is stored in a reference picture memory. A second basic picture is stored in compressed form in a buffer memory. The following steps are provided for a reconstruction of at least a first interpolated picture, which steps are executed iteratively in each case for the reconstruction of an interpolated picture: only a part of the second basic picture which is required for the reconstruction of a part of the first interpolated picture is decompressed in each case, the decompressed part of the second basic picture is stored in a second search area memory during a time in which the part of the first interpolated picture is reconstructed, and the part of the interpolated picture is reconstructed using the first basic picture and the decompressed part of the second basic picture.
Advantageous developments of the present invention are as follows.
A no longer required part of the decompressed part of the second basic picture is overwritten in the second search area memory by a following decompressed part, of the second basic picture, which is required for the reconstruction of a following part of the first interpolated picture.
An end part, which is no longer required for the reconstruction of a last part of a preceding interpolated picture, of the decompressed part of the second basic picture is overwritten in the second search area memory by a beginning part of the decompressed part, of the second basic picture, which is required for the reconstruction of a first part of a subsequent interpolated picture.
The first basic picture is stored in completely decompressed form in the reference picture memory.
In the event of a further basic picture being received, the second basic picture is completely decompressed. The completely decompressed second basic picture is stored in the reference picture memory. The further basic picture is stored in compressed form in the buffer memory.
One physical memory is used to realize the reference picture memory and the second search area memory.
The first basic picture is stored in compressed form in the reference picture memory. The following additional steps are provided for the reconstruction of the at least first interpolated picture, which steps are executed iteratively in each case for the reconstruction of an interpolated picture: only a part of the first basic picture which is required for the reconstruction of a part of the first interpolated picture is decompressed in each case, the decompressed part of the first basic picture is stored in a first search area memory during a time in which the part of the first interpolated picture is reconstructed, the part of the first interpolated picture is reconstructed using the decompressed part of the first basic picture and the decompressed part of the second basic picture, the decompressed part of the first basic picture is compressed, the compressed part of the first basic picture is stored in the reference picture memory, the decompr
Geib Heribert
Prange Stefan
Le Vu
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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