Image analysis – Image compression or coding
Reexamination Certificate
1998-03-12
2002-02-26
Couso, Jose L. (Department: 2721)
Image analysis
Image compression or coding
Reexamination Certificate
active
06351562
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a picture coding apparatus and a decoding apparatus which, when a video signal is to be encoded and decoded for storage or transmission, can realize high efficiency coding, and also a high speed search or reproduction of excellent efficiency.
2. Related Art of the Invention
Recently, MPEG (Moving Picture Expert Group) which is an international standard is typical of video coding.
According to MPEG, intrapicture coding is first conducted, motion vectors of a P-frame or a B-frame are detected on the basis of the intrapicture-decoded picture (I-frame) corresponding to the coding, motion compensation prediction of the detected motion vectors is conducted based on the motion vectors, and a difference between a motion compensated picture obtained by the motion compensation and the picture to be encoded is encoded. Namely, MPEG is a coding method of the intrapicture/interpicture selection type in which the intrapicture-decoded picture and the intrapicture coding of the picture are combined with each other.
In a coding method of the intrapicture/interpicture selection type, in order to prevent error propagation from occurring or enable an encoded picture to be reproduced from the middle irrespective of the contents of a moving picture, intrapicture coding is conducted with a predetermined period. When a moving picture is to be subjected to high speed reproduction, therefore, only a picture which has undergone intrapicture coding is extracted and then decoded to obtain a reproduced picture.
FIG. 10
is a block diagram of a high-speed reproduction apparatus in which an intrapicture-coded picture is extracted and then decoded. In the figure,
1
designates a coded input signal,
2
designates intrapicture-coded picture extracting means,
3
designates an intrapicture-coded signal,
4
designates intrapicture-coded picture decoding means, and
5
designates a decoded output signal.
The operation of the thus configured high-speed reproduction apparatus will be described. The intrapicture-coded picture extracting means
2
extracts only a picture which has undergone intrapicture coding, from the coded input signal
1
which has been subjected to coding of the intrapicture/interpicture selection type, and outputs the intrapicture-coded signal
3
. The intrapicture-coded picture decoding means
4
decodes the intrapicture-coded signal
3
and outputs the decoded output signal
5
. In this way, high-speed reproduction is conducted by extracting only an intrapicture-coded picture and decoding it.
In the high-speed reproduction apparatus, however, a P-frame or B-frame cannot be used in high-speed reproduction unless a I-frame or P-frame which is to be referred is decoded. Consequently, it is difficult to produce a high-speed reproduction apparatus which can smoothly conduct high-speed reproduction.
Even when only a part of a picture is updated, moreover, the previous picture must be updated. This causes the amount of information to be processed for high-speed reproduction, to be increased.
Since reproduction is performed at fixed intervals, it is difficult to conduct high-speed reproduction or a high-speed scene search in accordance with a change in contents of a picture.
Coding of pixel value information for a conventional picture scene is conducted on a single layer. In other words, pixel value information of the whole contents of one scene of a picture are completed on a single layer, and coding is conducted on each of the pixel value information on the single layer. When pixel value information which is completed on a single layer is to be encoded, the need for efficiently conducting the coding is growingly increased.
However, conventional means for encoding pixel value information which is completed on a single layer has a problem in that, even when a pixel which is not required to be encoded exists in the single layer, coding must be conducted with considering the value of the pixel and therefore the amount of information to be encoded is increased so that the processing speed is reduced.
SUMMARY OF THE INVENTION
According to the invention, a technique of layered coding is employed in which a moving picture is separated into layers such as a background, a foreground, and characters or pictures are separately prepared as one layer and coding is conducted on each layer. As a novel technique of coding a moving picture, the inventors have proposed in another patent application a technique of layered coding which uses a representative picture structure and global motion compensation.
FIG.
11
(
a
) is a diagram illustrating a layered structure. A final output picture is generated by synthesizing a foreground layer with a background layer. In each layer, coding is conducted by using a representative picture (template) structure and global motion compensation. Global motion compensation is a method in which motion of the whole picture is represented by global motion parameters such as translation, rotation, zooming, and reduction, motion compensation is conducted, and a predictive coded picture is generated. In the method, a predictive differential signal may be encoded or predictive differential signal coding may be omitted.
FIG.
11
(
b
) is a diagram illustrating the representative picture structure. Each layer is tracked along the time series, and a picture which represents each scene is selected as a representative picture. Examples of selecting a representative picture are listed below:
1. A picture which, in motion compensation, exhibits a minimum differential signal after motion compensation is selected.
2. A picture which is easy to search in a search process is artificially selected.
3. The first picture in a scene is selected.
In each scene, global motion compensation is conducted while using the representative picture of the scene as the reference picture, and a predictive coded picture is generated. As the representative picture to be referred, a representative picture of the scene, or a picture which has been selected as the representative picture in a previous scene may be selected. In other words, there is a possibility that the same representative picture is referred in a plurality of scenes. Such a scene may be a scene between scene changes in a picture, or a small scene which is obtained by partitioning in accordance with the groups of motions of the object. Alternatively, the scene may be deemed as a scene which is united in contents of a picture.
To comply with this, it is an object of the invention to provide a picture coding apparatus and a decoding apparatus for the coding apparatus which can conduct a search or reproduction wherein stress is placed on rapidness or wherein stress is placed on rapidness and also on continuity.
It is another object of the invention to provide a picture coding apparatus and a decoding apparatus for the coding apparatus which can efficiently encode and decode a picture signal.
Specifically, an object of the invention is to provide a picture decoding apparatus which can conduct high speed reproduction rapidly and efficiently with using a representative picture structure and a layered structure in layered coding which uses a representative picture structure and global motion compensation.
In the picture coding apparatus of the invention, even when the same representative picture is referred plural times in a plurality of scenes in the case where a coded signal consisting of representative pictures representing scenes of a picture and predictive coded pictures referring the representative pictures is to be encoded, reference relationships are encoded as additional information, and therefore it is possible to realize high-efficiency coding in which waste such as duplication of encoding the same representative picture is eliminated. In addition to the reference relationships, significance in contents of the time series of representative pictures may be encoded so that, in decoding associated with a high speed search or high speed reproduction, only a representative pict
Kadono Shinya
Tsuda Kenjiro
Couso Jose L.
Ratner & Prestia
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