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

• US 20030174776A1
• Filed: 01/30/2003
• Published: 09/18/2003
• Est. Priority Date: 06/25/1997
• Status: Active Grant

• Current Assignee: Nippon Telegraph and Telephone Corporation
• Original Assignee: Nippon Telegraph and Telephone Corporation
• Inventors: Shimizu, Atsushi, Watanabe, Hiroshi, Kamikura, Kazuto, Takamura, Seishi, Sagata, Atsushi, Jozawa, Hirohisa
• Granted Patent: US 7,206,346 B2
• Time in Patent Office: Days
• US Class Current: 375/240.16
• CPC Class Codes: H04N 19/51 Motion estimation or motion compensation
• CPC Class Codes: H04N 19/517 by encoding
• CPC Class Codes: H04N 19/52 by predictive encoding
• CPC Class Codes: H04N 19/527 Global motion vector estimation
• CPC Class Codes: H04N 19/537 Motion estimation other than block-based

Abstract

A motion vector predictive encoding method, a motion vector decoding method, a predictive encoding apparatus, a decoding apparatuses, and storage media storing motion vector predictive encoding and decoding programs are provided, thereby reducing the amount of generated code with respect to the motion vector, and improving the efficiency of the motion-vector prediction. If the motion-compensating mode of the target small block to be encoded is the global motion compensation, the encoding mode of an already-encoded small block is the interframe coding mode, and the motion-compensating mode of the already-encoded small block is the global motion compensation, then the motion vector of the translational motion model is determined for each pixel of the already-encoded small block, based on the global motion vector (steps S1-S5). Next, the representative motion vector is calculated as the predicted vector, based on the motion vector of each pixel of the already-encoded small block (step S6). Finally, the prediction error is calculated for each component of the motion vector and each prediction error is encoded (steps S7 and S8).

Claims

1. A motion vector predictive encoding method in which a target frame to be encoded is divided into small blocks and a motion-compensating method to be applied to each target small block to be encoded is selectable from among a plurality of motion-compensating methods, wherein:

when the motion vector of the target small block is predicted based on the motion vector of an already-encoded small block, if the motion model of the motion vector of the target small block differs from the motion model of the motion vector of the already-encoded small block, then the motion vector of the target small block is predicted by converting the motion vector of the already-encoded small block for the prediction into one suitable for the motion model of the motion vector used in the motion-compensating method of the target small block, and calculating a predicted vector, and a prediction error of the motion vector is encoded.

4. A motion vector predictive encoding method as claimed in any one of claims 1-3, wherein if the value of the predicted vector with respect to the motion vector of the target small block is not within a predetermined range, the predicted vector is clipped so as to have a value within the predetermined range.

5. A motion vector predictive encoding method as claimed in any one of claims 1-3, wherein if the value of the predicted vector with respect to the motion vector of the target small block is not within a predetermined range, the value of the predicted vector is set to 0.

6. A motion vector decoding method for decoding a motion vector which was encoded using the motion vector predictive encoding method as claimed in claim 1, wherein if the motion model of the motion vector of a target small block to be decoded differs from the motion model of the motion vector of the already-decoded small block, then the motion vector of the already-decoded small block is converted into one suitable for the motion model of the motion vector used in the motion-compensating method of the target small block, and a predicted vector with respect to the motion vector of the target small block is calculated, and the motion vector is decoded by adding the prediction error to the predicted vector.

9. A motion vector decoding method as claimed in any one of claims 6-8, wherein if the value of the predicted vector is not within a predetermined range, the predicted vector is clipped so as to have a value within the predetermined range.

10. A motion vector decoding method as claimed in any one of claims 6-8, wherein if the value of the predicted vector is not within a predetermined range, the value of the predicted vector is set to 0.

11. A motion vector predictive encoding method as claimed in claim 1, wherein when the motion vector of the small block in any motion model is converted into a motion vector in another motion model having fewer parameters with respect to the motion vector than parameters of the above motion model, a representative motion vector of the small block is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

14. A motion vector predictive encoding method as claimed in claim 4, wherein when the motion vector of the small block in any motion model is converted into a motion vector in another motion model having fewer parameters with respect to the motion vector than parameters of the above motion model, a representative motion vector of the small block is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

15. A motion vector predictive encoding method as claimed in claim 5, wherein when the motion vector of the small block in any motion model is converted into a motion vector in another motion model having fewer parameters with respect to the motion vector than parameters of the above motion model, a representative motion vector of the small block is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

16. A motion vector decoding method as claimed in claim 6, wherein when the motion vector of the small block in any motion model is converted into a motion vector in another motion model having fewer parameters with respect to the motion vector than parameters of the above motion model, a representative motion vector of the small block is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

19. A motion vector decoding method as claimed in claim 9, wherein when the motion vector of the small block in any motion model is converted into a motion vector in another motion model having fewer parameters with respect to the motion vector than parameters of the above motion model, a representative motion vector of the small block is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

20. A motion vector decoding method as claimed in claim 10, wherein when the motion vector of the small block in any motion model is converted into a motion vector in another motion model having fewer parameters with respect to the motion vector than parameters of the above motion model, a representative motion vector of the small block is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

21. A motion vector predictive encoding method as claimed in claim 1, wherein when the motion vector of the small block in any motion model is converted into a motion vector in a translational motion model, a representative motion vector of the small block is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

24. A motion vector predictive encoding method as claimed in claim 4, wherein when the motion vector of the small block in any motion model is converted into a motion vector in a translational motion model, a representative motion vector of the small block is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

25. A motion vector predictive encoding method as claimed in claim 5, wherein when the motion vector of the small block in any motion model is converted into a motion vector in a translational motion model, a representative motion vector of the small block is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

26. A motion vector decoding method as claimed in claim 6, wherein when the motion vector of the small block in any motion model is converted into a motion vector in a translational motion model, a representative motion vector of the small block is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

29. A motion vector decoding method as claimed in claim 9, wherein when the motion vector of the small block in any motion model is converted into a motion vector in a translational motion model, a representative motion vector of the small block is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

30. A motion vector decoding method as claimed in claim 10, wherein when the motion vector of the small block in any motion model is converted into a motion vector in a translational motion model, a representative motion vector of the small block is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

31. A motion vector predictive encoding method as claimed in claim 21, wherein in the calculation of the representative motion vector, each component of the representative motion vector is set to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

34. A motion vector predictive encoding method as claimed in claim 24, wherein in the calculation of the representative motion vector, each component of the representative motion vector is set to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

35. A motion vector predictive encoding method as claimed in claim 25, wherein in the calculation of the representative motion vector, each component of the representative motion vector is set to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

36. A motion vector decoding method as claimed in claim 26, wherein in the calculation of the representative motion vector, each component of the representative motion vector is set to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

39. A motion vector decoding method as claimed in claim 29, wherein in the calculation of the representative motion vector, each component of the representative motion vector is set to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

40. A motion vector decoding method as claimed in claim 30, wherein in the calculation of the representative motion vector, each component of the representative motion vector is set to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

2. A motion vector predictive encoding method in which a target frame to be encoded is divided into small blocks and a global motion-compensating method and a local motion-compensating method are switchable for each target small block to be encoded, wherein:

when the motion vector of the target small block is predicted based on the motion vector of an already-encoded small block, if the motion-compensating method of the target small block differs from the motion-compensating method of the already-encoded small block, then the motion vector of the target small block is predicted by converting the format of the motion vector of the already-encoded small block for the prediction into a format of the motion vector used in the motion-compensating method of the target small block, and a prediction error of the motion vector is encoded.

3. A motion vector predictive encoding method as claimed in claim 2, wherein if the motion-compensating method used for the target small block is the local motion-compensating method and the motion-compensating method used for the already-encoded small block for the prediction is the global motion-compensating method, then a local motion vector of the already-encoded small block is calculated based on the global motion vector, a predicted vector with respect to the motion vector of the target small block is calculated, and the prediction error of the motion vector is encoded.

7. A motion vector decoding method for decoding a motion vector which was encoded using the motion vector predictive encoding method as claimed in claim 2, wherein if the motion-compensating method of the target small block to be decoded differs from the motion-compensating method of the already-decoded small block, then the format of the motion vector of the already-decoded small block is converted into a format of the motion vector used in the motion-compensating method of the target small block, and a predicted vector of the motion vector of the target small block is calculated, and the motion vector is decoded by adding the prediction error to the predicted vector.

8. A motion vector decoding method for decoding a motion vector which was encoded using the motion vector predictive encoding method as claimed in claim 3, wherein if the motion-compensating method used for the target small block to be decoded is the local motion-compensating method and the motion-compensating method used for the already-decoded small block for the prediction is the global motion-compensating method, then a local motion vector of the already-decoded small block is calculated based on the global motion vector, a predicted vector with respect to the motion vector of the target small block is calculated, and the motion vector is decoded by adding the prediction error to the predicted vector.

12. A motion vector predictive encoding method as claimed in claim 2, wherein when the motion vector of the small block in any motion model is converted into a motion vector in another motion model having fewer parameters of the motion vector than parameters of the above motion model, a representative motion vector of the small block is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

13. A motion vector predictive encoding method as claimed in claim 3, wherein when the motion vector of the small block in any motion model is converted into a motion vector in another motion model having fewer parameters with respect to the motion vector than parameters of the above motion model, a representative motion vector of the small block is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

17. A motion vector decoding method as claimed in claim 7, wherein when the motion vector of the small block in any motion model is converted into a motion vector in another motion model having fewer parameters with respect to the motion vector than parameters of the above motion model, a representative motion vector of the small block is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

18. A motion vector decoding method as claimed in claim 8, wherein when the motion vector of the small block in any motion model is converted into a motion vector in another motion model having fewer parameters with respect to the motion vector than parameters of the above motion model, a representative motion vector of the small block is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

22. A motion vector predictive encoding method as claimed in claim 2, wherein when the motion vector of the small block in any motion model is converted into a motion vector in a translational motion model, a representative motion vector of the small block is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

23. A motion vector predictive encoding method as claimed in claim 3, wherein when the motion vector of the small block in any motion model is converted into a motion vector in a translational motion model, a representative motion vector of the small block is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

27. A motion vector decoding method as claimed in claim 7, wherein when the motion vector of the small block in any motion model is converted into a motion vector in a translational motion model, a representative motion vector of the small block is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

28. A motion vector decoding method as claimed in claim 8, wherein when the motion vector of the small block in any motion model is converted into a motion vector in a translational motion model, a representative motion vector of the small block is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

32. A motion vector predictive encoding method as claimed in claim 22, wherein in the calculation of the representative motion vector, each component of the representative motion vector is set to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

33. A motion vector predictive encoding method as claimed in claim 23, wherein in the calculation of the representative motion vector, each component of the representative motion vector is set to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

37. A motion vector decoding method as claimed in claim 27, wherein in the calculation of the representative motion vector, each component of the representative motion vector is set to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

38. A motion vector decoding method as claimed in claim 28, wherein in the calculation of the representative motion vector, each component of the representative motion vector is set to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

41. A motion vector predictive encoding method in which interframe prediction is performed using one of a global motion-compensating method for predicting a global motion or deformation of an entire frame and a local motion-compensating method for predicting a local motion for each block, the encoding method comprising the steps of:

determining the motion-compensating mode used for a target small block to be encoded;

determining the encoding mode of an already-encoded small block if the motion-compensating mode of the target small block is the local motion compensation;

setting the value of the motion vector of the already-encoded small block to 0 if the encoding mode of the already-encoded small block is the intraframe coding;

determining the motion-compensating mode of the already-encoded small block if the encoding mode of the already-encoded small block is the interframe coding;

calculating a motion vector for each pixel of the already-encoded small block based on global motion parameters if the motion-compensating mode of the already-encoded small block is the global motion compensation;

calculating a representative motion vector of the already-encoded small block by using a predetermined method, based on the motion vector determined for each pixel;

determining whether the value of the representative motion vector is within a predetermined range;

clipping the representative motion vector to have a value within the predetermined range or setting the value of the representative motion vector to 0 if the value of the representative motion vector is not within a predetermined range;

calculating a prediction error which is a difference between the motion vector of the already-encoded small block and a predicted vector; and

encoding the calculated prediction error.

42. A motion vector decoding method corresponding to the motion vector predictive encoding method as claimed in claim 41, the decoding method comprising the steps of:

determining the motion-compensating mode used for the target small block to be decoded;

decoding the prediction error of the motion vector if the motion-compensating mode of the target small block is the local motion compensation;

determining the encoding mode of the already-decoded small block;

setting the value of the motion vector of the already-decoded small block to 0 if the encoding mode of the already-decoded small block is the intraframe coding;

determining the motion-compensating mode of the already-decoded small block if the encoding mode of the already-decoded small block is the interframe coding;

calculating a motion vector for each pixel of a reference block based on global motion parameters if the motion-compensating mode of the already-decoded small block is the global motion compensation;

calculating a representative motion vector of the block by using a predetermined method, based on the motion vector determined for each pixel;

determining whether the value of the representative motion vector is within a predetermined range;

clipping the representative motion vector to have a value within the predetermined range or setting the value of the representative motion vector to 0 if the value of the representative motion vector is not within a predetermined range; and

adding the prediction error of the already-decoded small block to the predicted vector.

43. A motion vector predictive encoding apparatus in which a target frame to be encoded is divided into small blocks and a global motion-compensating method and a local motion-compensating method are switchable for each target small block to be encoded, the apparatus comprising:

already-encoded small block storing means for storing an input local motion vector of a target small block to be encoded, and outputting the stored motion vector as a local motion vector of an already-encoded small block when a next local motion vector of a target small block is input;

predicted vector calculating means for calculating a predicted vector of the motion vector of the target small block by converting the format of an input global motion vector into the format of the local motion vector for each small block, and outputting the calculated predicted vector as the predicted vector of a target small block when a next local motion vector of the target small block is input;

predicted vector choosing means for choosing the predicted vector calculated by the predicted vector calculating means if the motion-compensating method of the target small block is the local motion-compensating method and the motion-compensating method of the already-encoded small block for prediction is the global motion-compensating method, or choosing the local motion vector of the already-encoded small block output from the already-encoded small block storing means as a predicted vector if the motion-compensating methods of the target small block and the already-encoded small block are the local motion-compensating method;

prediction error outputting means for outputting a prediction error with respect to the motion vector of the target small block based on the predicted vector chosen by the predicted vector choosing means and the input motion vector of the target small block; and

encoding means for encoding the prediction error output from the prediction error outputting means and the input global motion vector.

44. A motion vector predictive encoding apparatus as claimed in claim 43, further comprising:

clipping means for clipping the predicted vector calculated by the predicted vector calculating means to have a value within a predetermined range if the value of the predicted vector is not within the predetermined range.

45. A motion vector predictive encoding apparatus as claimed in claim 43, further comprising:

clipping means for setting the value of the converted local motion vector of the already-encoded small block to 0 if the value of the predicted vector calculated by the predicted vector calculating means is not within a predetermined range.

46. A motion vector decoding apparatus for decoding the motion vector encoded by the motion vector predictive encoding apparatus as claimed in claim 43, the decoding apparatus comprising:

decoding means for the encoded prediction error of the target small block to be decoded and the encoded global motion vector;

already-decoded small block storing means for storing the local motion vector of the already-decoded small block, which was decoded by the motion vector decoding apparatus, and outputting the stored motion vector when next the prediction error is decoded by the decoding means;

predicted vector calculating means for calculating, when the global motion vector is decoded by the decoding means, a predicted vector of the motion vector of the target small block by converting the global motion vector into a local motion vector for each small block, and outputting the calculated predicted vector when next the prediction error is decoded by the decoding means;

predicted vector choosing means for choosing the predicted vector output from the predicted vector calculating means if the motion-compensating method with respect to the prediction error decoded by the decoding means is the local motion-compensating method and the motion-compensating method of the already-decoded small block for prediction is the global motion-compensating method, or choosing the local motion vector of the already-decoded small block output from the already-decoded small block storing means as a predicted vector if the motion-compensating methods of the prediction error and the already-decoded small block are the local motion-compensating method; and

motion vector decoding means for decoding the motion vector by adding the prediction error decoded by the above decoding means to the predicted vector chosen by the predicted vector choosing means.

47. A motion vector decoding apparatus as claimed in claim 46, further comprising:

clipping means for clipping the predicted vector calculated by the predicted vector calculating means to have a value within a predetermined range if the value of the predicted vector is not within the predetermined range.

48. A motion vector decoding apparatus as claimed in claim 46, further comprising:

clipping means for setting the value of the converted local motion vector of the already-encoded small block to 0 if the value of the predicted vector calculated by the predicted vector calculating means is not within a predetermined range.

49. A motion vector predictive encoding apparatus as claimed in any one of claims 43-45, wherein when the predicted vector calculating means converts the motion vector of the small block in any motion model into a motion vector in another motion model having fewer parameters of the motion vector than parameters of the above motion model, a representative motion vector of the small block is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

50. A motion vector decoding apparatus as claimed in any one of claims 46-48, wherein when the predicted vector calculating means converts the motion vector of the small block in any motion model into a motion vector in another motion model having fewer parameters of the motion vector than parameters of the above motion model, a representative motion vector of the small block is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

51. A motion vector predictive encoding apparatus as claimed in any one of claims 43-45, wherein when the predicted vector calculating means converts the motion vector of the small block in any motion model into a motion vector in a translational motion model, a representative motion vector of the small block is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

52. A motion vector decoding apparatus as claimed in any one of claims 46-48, wherein when the predicted vector calculating means converts the motion vector of the small block in any motion model into a motion vector in a translational motion model, a representative motion vector of the small block is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

53. A motion vector predictive encoding apparatus as claimed in claim 51, wherein when the predicted vector calculating means calculates the predicted vector, each component of the predicted vector is set to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

54. A motion vector decoding apparatus as claimed in claim 52, wherein when the predicted vector calculating means calculates the predicted vector, each component of the representative motion vector is set to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

55. A computer-readable storage medium storing a motion vector predictive encoding program for executing motion vector predictive encoding in which a target frame to be encoded is divided into small blocks and a motion-compensating method to be applied to each target small block to be encoded is selectable from among a plurality of motion-compensating methods, the program including the steps of:

calculating a predicted vector when the motion vector of the target small block is predicted based on the motion vector of an already-encoded small block, wherein if the motion model of the motion vector of the target small block differs from the motion model of the motion vector of the already-encoded small block, then the motion vector of the already-encoded small block for the prediction is converted into a motion vector suitable for the motion model used in the motion-compensating method of the target small block; and

predicting the motion vector of the already-encoded small block based on the calculated predicted vector, and encoding a prediction error of the motion vector.

58. A computer-readable storage medium storing a motion vector predictive encoding program as claimed in any one of claims 55-57, including the step of:

clipping the predicted vector with respect to the motion vector of the target small block so as to have a value within a predetermined range if the value of the predicted vector is not within the predetermined range.

59. A computer-readable storage medium storing a motion vector predictive encoding program as claimed in any one of claims 55-57, including the step of:

setting the value of the predicted vector with respect to the motion vector of the target small block to 0 if the value of the predicted vector is not within a predetermined range.

60. A computer-readable storage medium storing a motion vector decoding program for decoding the motion vector which was encoded by executing the motion vector predictive encoding program as claimed in claim 55, the decoding program including the steps of:

converting the motion vector of the already-decoded small block into a motion vector suitable for the motion model used in the motion-compensating method of a target small block to be decoded if the motion model of the motion vector of the target small block differs from the motion model of the motion vector of the already-decoded small block, and calculating a predicted vector with respect to the motion vector of the target small block; and

decoding the motion vector by adding the prediction error to the predicted vector.

63. A computer-readable storage medium storing a motion vector decoding program as claimed in any one of claims 60-62, including the step of:

clipping the predicted vector so as to have a value within a predetermined range if the value of the predicted vector is not within the predetermined range.

64. A computer-readable storage medium storing a motion vector decoding program as claimed in any one of claims 60-62, including the step of:

setting the value of the predicted vector to 0 if the value of the predicted vector is not within a predetermined range.

65. A computer-readable storage medium storing a motion vector predictive encoding program as claimed in claim 55, including the step of:

calculating a representative motion vector of the small block when the motion vector of the small block in any motion model is converted into a motion vector in another motion model having fewer parameters of the motion vector than parameters of the above motion model, wherein the representative motion vector is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

68. A computer-readable storage medium storing a motion vector predictive encoding program as claimed in claim 58, including the step of:

calculating a representative motion vector of the small block when the motion vector of the small block in any motion model is converted into a motion vector in another motion model having fewer parameters of the motion vector than parameters of the above motion model, wherein the representative motion vector is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

69. A computer-readable storage medium storing a motion vector predictive encoding program as claimed in claim 59, including the step of:

calculating a representative motion vector of the small block when the motion vector of the small block in any motion model is converted into a motion vector in another motion model having fewer parameters of the motion vector than parameters of the above motion model, wherein the representative motion vector is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

70. A computer-readable storage medium storing a motion vector decoding program as claimed in claim 60, including the step of:

calculating a representative motion vector of the small block when the motion vector of the small block in any motion model is converted into a motion vector in another motion model having fewer parameters of the motion vector than parameters of the above motion model, wherein the representative motion vector is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

73. A computer-readable storage medium storing a motion vector decoding program as claimed in claim 63, including the step of:

calculating a representative motion vector of the small block when the motion vector of the small block in any motion model is converted into a motion vector in another motion model having fewer parameters of the motion vector than parameters of the above motion model, wherein the representative motion vector is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

74. A computer-readable storage medium storing a motion vector decoding program as claimed in claim 64, including the step of:

calculating a representative motion vector of the small block when the motion vector of the small block in any motion model is converted into a motion vector in another motion model having fewer parameters of the motion vector than parameters of the above motion model, wherein the representative motion vector is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

75. A computer-readable storage medium storing a motion vector predictive encoding program as claimed in claim 55, including the step of:

calculating a representative motion vector of the small block when the motion vector of the small block in any motion model is converted into a motion vector in a translational motion model, wherein the representative motion vector is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

78. A computer-readable storage medium storing a motion vector predictive encoding program as claimed in claim 58, including the step of:

calculating a representative motion vector of the small block when the motion vector of the small block in any motion model is converted into a motion vector in a translational motion model, wherein the representative motion vector is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

79. A computer-readable storage medium storing a motion vector predictive encoding program as claimed in claim 59, including the step of:

calculating a representative motion vector of the small block when the motion vector of the small block in any motion model is converted into a motion vector in a translational motion model, wherein the representative motion vector is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

80. A computer-readable storage medium storing a motion vector decoding program as claimed in claim 60, including the step of:

calculating a representative motion vector of the small block when the motion vector of the small block in any motion model is converted into a motion vector in a translational motion model, wherein the representative motion vector is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

83. A computer-readable storage medium storing a motion vector decoding program as claimed in claim 63, including the step of:

calculating a representative motion vector of the small block when the motion vector of the small block in any motion model is converted into a motion vector in a translational motion model, wherein the representative motion vector is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

84. A computer-readable storage medium storing a motion vector decoding program as claimed in claim 64, including the step of:

calculating a representative motion vector of the small block when the motion vector of the small block in any motion model is converted into a motion vector in a translational motion model, wherein the representative motion vector is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

85. A computer-readable storage medium storing a motion vector predictive encoding program as claimed in claim 75, including the step of:

calculating the representative motion vector by setting each component thereof to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

88. A computer-readable storage medium storing a motion vector predictive encoding program as claimed in claim 78, including the step of:

calculating the representative motion vector by setting each component thereof to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

89. A computer-readable storage medium storing a motion vector predictive encoding program as claimed in claim 79, including the step of:

calculating the representative motion vector by setting each component thereof to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

90. A computer-readable storage medium storing a motion vector decoding program as claimed in claim 80, including the step of:

calculating the representative motion vector by setting each component thereof to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

93. A computer-readable storage medium storing a motion vector decoding program as claimed in claim 83, including the step of:

calculating the representative motion vector by setting each component thereof to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

94. A computer-readable storage medium storing a motion vector decoding program as claimed in claim 84, including the step of:

calculating the representative motion vector by setting each component thereof to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

56. A computer-readable storage medium storing a motion vector predictive encoding program for executing motion vector predictive encoding in which a target frame to be encoded is divided into small blocks and a global motion-compensating method and a local motion-compensating method are switchable for each target small block to be encoded, the program including the steps of:

converting the format of the motion vector when the motion vector of the target small block is predicted based on the motion vector of an already-encoded small block, wherein if the motion-compensating method of the target small block differs from the motion-compensating method of the already-encoded small block, then the format of the motion vector of the already-encoded small block for the prediction is converted into a format of the motion vector used in the motion-compensating method of the target small block; and

predicting the motion vector of the already-encoded small block based on the predicted vector in the converted format, and encoding a prediction error of the motion vector.

57. A computer-readable storage medium storing a motion vector predictive encoding program as claimed in claim 56, including the steps of:

calculating a local motion vector of the already-encoded small block based on the global motion vector if the motion-compensating method used for the target small block is the local motion-compensating method and the motion-compensating method used for the already-encoded small block for the prediction is the global motion-compensating method; and

calculating a predicted vector with respect to the motion vector of the target small block, and encoding the prediction error of the motion vector.

61. A computer-readable storage medium storing a motion vector decoding program for decoding the motion vector which was encoded by executing the motion vector predictive encoding program as claimed in claim 56, the decoding program including the steps of:

converting the format of the motion vector of the already-decoded small block into a format of the motion vector used in the motion-compensating method of the target small block to be decoded if the motion-compensating method of the target small block differs from the motion-compensating method of the already-decoded small block, and calculating a predicted vector of the motion vector of the target small block; and

decoding the motion vector by adding the prediction error to the predicted vector.

62. A computer-readable storage medium storing a motion vector decoding program for decoding the motion vector which was encoded by executing the motion vector predictive encoding program as claimed in claim 57, the decoding program including the steps of:

calculating a local motion vector of the already-decoded small block for the prediction based on the global motion vector if the motion-compensating method used for the target small block to be decoded is the local motion-compensating method and the motion-compensating method used for the already-decoded small block is the global motion-compensating method, and calculating a predicted vector with respect to the motion vector of the target small block; and

decoding the motion vector by adding the prediction error to the predicted vector.

66. A computer-readable storage medium storing a motion vector predictive encoding program as claimed in claim 56, including the step of:

calculating a representative motion vector of the small block when the motion vector of the small block in any motion model is converted into a motion vector in another motion model having fewer parameters of the motion vector than parameters of the above motion model, wherein the representative motion vector is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

67. A computer-readable storage medium storing a motion vector predictive encoding program as claimed in claim 57, including the step of:

calculating a representative motion vector of the small block when the motion vector of the small block in any motion model is converted into a motion vector in another motion model having fewer parameters of the motion vector than parameters of the above motion model, wherein the representative motion vector is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

71. A computer-readable storage medium storing a motion vector decoding program as claimed in claim 61, including the step of:

calculating a representative motion vector of the small block when the motion vector of the small block in any motion model is converted into a motion vector in another motion model having fewer parameters of the motion vector than parameters of the above motion model, wherein the representative motion vector is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

72. A computer-readable storage medium storing a motion vector decoding program as claimed in claim 62, including the step of:

calculating a representative motion vector of the small block when the motion vector of the small block in any motion model is converted into a motion vector in another motion model having fewer parameters of the motion vector than parameters of the above motion model, wherein the representative motion vector is calculated based on the motion vector in the other motion model determined for each pixel in the small block.

76. A computer-readable storage medium storing a motion vector predictive encoding program as claimed in claim 56, including the step of:

calculating a representative motion vector of the small block when the motion vector of the small block in any motion model is converted into a motion vector in a translational motion model, wherein the representative motion vector is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

77. A computer-readable storage medium storing a motion vector predictive encoding program as claimed in claim 57, including the step of:

calculating a representative motion vector of the small block when the motion vector of the small block in any motion model is converted into a motion vector in a translational motion model, wherein the representative motion vector is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

81. A computer-readable storage medium storing a motion vector decoding program as claimed in claim 61, including the step of:

calculating a representative motion vector of the small block when the motion vector of the small block in any motion model is converted into a motion vector in a translational motion model, wherein the representative motion vector is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

82. A computer-readable storage medium storing a motion vector decoding program as claimed in claim 62, including the step of:

calculating a representative motion vector of the small block when the motion vector of the small block in any motion model is converted into a motion vector in a translational motion model, wherein the representative motion vector is calculated based on the motion vector in the translational motion model determined for each pixel in the small block.

86. A computer-readable storage medium storing a motion vector predictive encoding program as claimed in claim 76, including the step of:

calculating the representative motion vector by setting each component thereof to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

87. A computer-readable storage medium storing a motion vector predictive encoding program as claimed in claim 77, including the step of:

calculating the representative motion vector by setting each component thereof to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

91. A computer-readable storage medium storing a motion vector decoding program as claimed in claim 81, including the step of:

calculating the representative motion vector by setting each component thereof to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

92. A computer-readable storage medium storing a motion vector decoding program as claimed in claim 82, including the step of:

calculating the representative motion vector by setting each component thereof to one of the average, intermediate value, median, mode, maximum value, and minimum value, which is calculated for each component of the motion vector in the translational motion model of each pixel in the small block.

95. A computer-readable storage medium storing a motion vector predictive encoding program in which interframe prediction is performed using one of a global motion-compensating method for predicting a global motion or deformation of an entire frame and a local motion-compensating method for predicting a local motion for each block, the program including the steps of:

determining the motion-compensating mode used for a target small block to be encoded;

determining the encoding mode of an already-encoded small block if the motion-compensating mode of the target small block is the local motion compensation;

setting the value of the motion vector of the already-encoded small block to 0 if the encoding mode of the already-encoded small block is the intraframe coding;

determining the motion-compensating mode of the already-encoded small block if the encoding mode of the already-encoded small block is the interframe coding;

calculating a motion vector for each pixel of the already-encoded small block based on global motion parameters if the motion-compensating mode of the already-encoded small block is the global motion compensation;

calculating a representative motion vector of the already-encoded small block by using a predetermined method, based on the motion vector determined for each pixel;

determining whether the value of the representative motion vector is within a predetermined range;

clipping the representative motion vector to have a value within the predetermined range or setting the value of the representative motion vector to 0 if the value of the representative motion vector is not within a predetermined range;

calculating a prediction error which is a difference between the motion vector of the already-encoded small block and a predicted vector; and

encoding the calculated prediction error.

96. A computer-readable storage medium storing a motion vector decoding program for decoding the motion vector which was encoded by executing the motion vector predictive encoding program as claimed in claim 95, the decoding program including the steps of:

determining the motion-compensating mode used for the target small block to be decoded;

decoding the prediction error of the motion vector if the motion-compensating mode of the target small block is the local motion compensation;

determining the encoding mode of the already-decoded small block;

setting the value of the motion vector of the already-decoded small block to 0 if the encoding mode of the already-decoded small block is the intraframe coding;

determining the motion-compensating mode of the already-decoded small block if the encoding mode of the already-decoded small block is the interframe coding;

calculating a motion vector for each pixel of a reference block based on global motion parameters if the motion-compensating mode of the already-decoded small block is the global motion compensation;

calculating a representative motion vector of the block by using a predetermined method, based on the motion vector determined for each pixel;

determining whether the value of the representative motion vector is within a predetermined range;

clipping the representative motion vector to have a value within the predetermined range or setting the value of the representative motion vector to 0 if the value of the representative motion vector is not within a predetermined range; and

adding the prediction error of the already-decoded small block to the predicted vector.