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Motion vector predictive encoding method, motion vector decoding method, predictive encoding apparatus and decoding apparatus, and storage media storing motion vector predictive encoding and decoding programsRelated Patent Categories: Pulse Or Digital Communications, Bandwidth Reduction Or Expansion, Television Or Motion Video Signal, Predictive, Motion VectorMotion vector predictive encoding method, motion vector decoding method, predictive encoding apparatus and decoding apparatus, and storage media storing motion vector predictive encoding and decoding programs description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070183505, Motion vector predictive encoding method, motion vector decoding method, predictive encoding apparatus and decoding apparatus, and storage media storing motion vector predictive encoding and decoding programs. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention relates to motion vector predictive encoding and decoding methods, predictive encoding and decoding apparatuses, and storage media storing motion vector predictive encoding and decoding programs. These methods, apparatuses, and storage media are used for motion-compensating interframe prediction for motion picture encoding. BACKGROUND ART [0002] The interframe predictive coding method for coding motion pictures (i.e., video data) is known, in which an already-encoded frame is used as a prediction signal so as to reduce temporal redundancy. In order to improve the efficiency of the time-based prediction, a motion-compensating interframe prediction method is used in which a motion-compensated picture signal is used as a prediction signal. The number and the kinds of components of the motion vector used for the motion compensation are determined depending on the assumed motion model used as a basis. For example, in a motion model in which only translational movement is considered, the motion vector consists of components corresponding to horizontal and vertical motions. In another motion model in which extension and contraction are also considered in addition to the translational movement, the motion vector consists of components corresponding to horizontal and vertical motions, and a component corresponding to the extending or contracting motion. [0003] Generally, the motion compensation is executed for each small area obtained by dividing a picture into a plurality of areas such as small blocks, and each divided area has an individual motion vector. It is known that the motion vectors belonging to neighboring areas including adjacent small areas have a higher correlation. Therefore, in practice, the motion vector of an area to be encoded is predicted based on the motion vector of an area which neighbors the area to be encoded, and a prediction error generated at the prediction is variable-length-encoded so as to reduce the redundancy of the motion vector. [0004] In the moving-picture coding method ISO/IEC 11172-2 (MPEG-1), the picture to be encoded is divided into small blocks so as to motion-compensate each small block, and the motion vector of a small block to be encoded (hereinbelow, called the "target small block") is predicted based on the motion vector of a small block which has already been encoded. [0005] In the above MPEG-1, only translational motions can be compensated. It may be impossible to compensate more complicated motions with a simpler model, such as MPEG-1, which has few components of the motion vector. Accordingly, the efficiency of the interframe prediction can be improved by using a motion-compensating method which corresponds to a more complicated model having a greater number of components of the motion vector. However, when each small block is motion-compensated in such a method for a complicated motion model, the amount of codes generated when encoding the relevant motion vector is increased. [0006] An encoding method for avoiding such an increase of the amount of generated codes is known, in which the motion-vector encoding is performed using a method, selected from a plurality of motion-compensating methods, which minimizes the prediction error with respect to the target block. The following is an example of such an encoding method in which two motion-compensating methods are provided, one method corresponding to a translational motion model, the other corresponding to a translational motion and extending/contracting motion model, and one of the two motion-compensating methods is chosen. [0007] FIG. 9 shows a translational motion model (see part (a)) and a translational motion and extending/contracting motion model (see part (b)). In the translational motion model of part (a), the motion of a target object is represented using a translational motion component (x, y). In the translational motion and extending/contracting motion model of part (b), the motion of a target object is represented using a component (x, y, z) in which parameter Z for indicating the amount of extension or contraction of the target object is added to the translational motion component (x, y). In the example shown in FIG. 9, parameter Z has a value corresponding to the contraction (see part (b)). [0008] Accordingly, motion vector {right arrow over (v1)} of the translational motion model is represented by: {right arrow over (v1)}=(x, y) while motion vector {right arrow over (v2)} of the translational motion and extending/contracting motion model is represented by: {right arrow over (v2)}=(x, y, z) [0009] In the above formulas, x, y, and z respectively indicate horizontal, vertical, and extending/contracting direction components. Here, the unit for motion compensation is a small block, the active motion-compensating method may be switched for each small block in accordance with the present prediction efficiency, and the motion vector is predicted based on the motion vector of an already-encoded small block. [0010] If the motion-compensating method chosen for the target small block is the same as that adopted for the already-encoded small block, the prediction error of the motion vector is calculated by the following equations. [0011] For the translational motion model: d1x,y=v1x,y(i)-v1x,y(i-1) (1) [0012] For the translational motion and extending/contracting motion model: d2x,y,z=v2x,y,z(i)-v2x,y,z(i-1) (2) [0013] Here, v1 x, y (i) and v2 x, y, z (i) mean components of the motion vector of the target small block, while v1 x, y (i-1) and v2 x, y, z (i-1) mean components of the motion vector of a small block of the previous frame. [0014] As explained above, prediction errors d x, y and d x, y, z are calculated and encoded so as to transmit the encoded data to the decoding side. Even if the size of each small block is not the same in the motion-compensating method, the motion vector predictive encoding is similarly performed if the motion model is the same. [0015] If the motion-compensating method chosen for the target small block differs from that adopted for the already-encoded small block, or if intraframe coding is performed, then the predicted value for each component is set to 0 and the original values of each component of the target small block are transmitted to the decoding side. [0016] By using such an encoding method, the redundancy of the motion vector with respect to the motion-compensating interframe predictive encoding can be reduced and the amount of generated codes of the motion vector can be reduced. [0017] On the other hand, the motion vector which has been encoded using the above-described encoding method is decoded in a manner such that the prediction error is extracted from the encoded data sequence, and the motion vector of the small block to be decoded (i.e., the target small block) is decoded by adding the prediction error to the motion vector which has already been decoded. See the following equations. [0018] For the translational motion model: v1x,y(i)=v1x,y(i-1)+d1x,y (3) [0019] For the translational motion and extending/contracting motion model: v2x,y,z(i)=v2x,y,z(i-1)+d2x,y,z (4) [0020] Here, v1 x, y (i) and v2 x, y, z (i) mean components of the motion vector of the target small block, while v1 x, y (i-1) and v2 x, y, z (i-1) mean components of the already-decoded motion vector. [0021] In the model ISO/IEC 14496-2 (MPEG-4) under testing for international standardization in January, 1999, a similar motion-compensating method is adopted. The MPEG-4 adopts a global motion-compensating method for predicting the general change or movement of a picture caused by panning, tilting and zooming operations of the camera (refer to "MPEG-4 Video Verification Model Version 7.0", ISO/IEC JTC1/SC29/WG11N1682, MPEG Video Group, April, 1997). Hereinafter, the structure and the operational flow of the encoder using the global motion compensation will be explained with reference to FIG. 11. [0022] First, a picture to be encoded (i.e., target picture) 31 is input into global motion detector 34 so as to determine global motion parameters 35 with respect to the entire picture. In the MPEG-4, the projective transformation and the affine transformation may be used in the motion model. Continue reading about Motion vector predictive encoding method, motion vector decoding method, predictive encoding apparatus and decoding apparatus, and storage media storing motion vector predictive encoding and decoding programs... 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