Apparatus and method for coding moving picture

• US 20010007575A1
• Filed: 12/12/2000
• Published: 07/12/2001
• Est. Priority Date: 12/13/1999
• Status: Active Grant

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Katta, Noboru, Mori, Toshiaki, Ibaraki, Susumu
• Granted Patent: US 6,408,027 B2
• Time in Patent Office: Days
• US Class Current: 375/240.03
• CPC Class Codes: H04N 19/115 Selection of the code volume for a coding unit prior to coding
• CPC Class Codes: H04N 19/12 Selection from among a plurality of transforms or standards, e.g. selection between discrete cosine transform [DCT] and sub-band transform or selection between H.263 and H.264
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/13 Adaptive entropy coding, e.g. adaptive variable length coding [AVLC] or context adaptive binary arithmetic coding [CABAC]
• CPC Class Codes: H04N 19/137 Motion inside a coding unit, e.g. average field, frame or block difference
• CPC Class Codes: H04N 19/15 by monitoring actual compressed data size at the memory before deciding storage at the transmission buffer
• CPC Class Codes: H04N 19/152 by measuring the fullness of the transmission buffer
• CPC Class Codes: H04N 19/172 the region being a picture, frame or field
• CPC Class Codes: H04N 19/174 the region being a slice, e.g. a line of blocks or a group of blocks
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/91 Entropy coding, e.g. variable length coding [VLC] or arithmetic coding

Abstract

The present invention provides an apparatus and method for coding moving pictures, which reduces a delay time generated by buffering of a decoding apparatus in compressive coding of the moving pictures. In this invention, the target number of bits of one picture P as a target value of the number of generated bits per one picture is set as well as the upper limit number of bits uCg as an upper limit value of the number of generated bits of the picture is set. Then, when the cumulative number of generated bits Cg generated from the first macroblock to a macroblock which is being coded in the picture exceeds the upper limit number of bits uCg in the middle of the picture which is being coded, the coding of a macroblock is skipped to avoid underflow. When the cumulative number of generated bits Cg does not reach the target number of bits of one picture P after the picture has been coded to the end, the stuffing is performed so that the cumulative number of generated bits of one picture Cg reaches the target number of bits of one picture P.

Claims

1. A moving picture coding apparatus comprising:

a coding processing means for coding a video signal in a frame for each block of a prescribed area; and

a rate control means for controlling the coding processing means so that a generated code amount after coding of the video signal is fixed for each code amount control unit as a unit of the frame or a unit which is smaller than the frame.

2. The moving picture coding apparatus of

claim 1

wherein the rate control means comprises:

a generated code amount detection means for detecting a cumulative amount of generated codes as a cumulative value of amounts of codes generated from a first block to a block which is being coded in a code amount control unit which is being coded;

a target code amount calculation means for setting a target generated code amount per code amount control unit as a target value of accumulation of amounts of codes which are generated from a first block to a last block in the code amount control unit, and calculating a target code amount as a target value of accumulation of amounts of codes which are generated from the first block to a block which is being coded in the code amount control unit;

an upper limit code amount calculation means for calculating an upper limit code amount as an upper limit value of accumulation of generated code amounts per code amount control unit; and

a quantization scale calculation means for calculating a quantization scale of the block which is being coded, on the basis of the cumulative generated code amount calculated by the generated code amount detection means, the target code amount calculated by the target code amount calculation means, and the upper limit code amount calculated by the upper limit code amount calculation means.

3. The moving picture coding apparatus of

claim 2

wherein

when the cumulative generated code amount exceeds the upper limit code amount in the code amount control unit which is being coded, the quantization scale calculation means generates an underflow avoidance signal for skipping coding of a block in the code amount control unit by the coding processing means until the cumulative generated code amount becomes equal to or less than the upper limit code amount, thereby avoiding underflow, and

when the cumulative generated code amount of the code amount control unit which has been coded does not reach the target generated code amount per the code amount control unit, the quantization scale calculation means subtracts the cumulative generated code amount from the target generated code amount per code amount control unit, thereby calculating a stuffing code amount for a stuffing processing by the coding processing means.

4. The moving picture coding apparatus of

claim 2

wherein

the quantization scale calculation means obtains a tolerance generated code amount as a difference between the upper limit code amount and the target code amount as well as obtains a generated code amount error as a difference between the cumulative generated code amount and the target code amount, and calculates the quantization scale using a quantization scale decision function having inclinations which vary with values of the generated code amount error with respect to the tolerance generated code amount.

5. The moving picture coding apparatus of

claim 4

wherein

the quantization scale decision f unction has a smaller inclination in the vicinity of 0 of the generated code amount error with respect to the tolerance generated code amount, than in a part where the value of the generated code amount error with respect to the tolerance generated code amount is larger.

6. The moving picture coding apparatus of

claim 2

wherein

the target code amount calculation means obtains distribution of degree of coding difficulty in each code amount control unit when the coding of the code amount control unit has been finished, and calculates the target code amount of a block which is being coded in a subsequent code amount control unit on the basis of the obtained distribution of degree of coding difficulty.

7. The moving picture coding apparatus of

claim 4

or

6

wherein

the quantization scale decision function has a reference quantization scale as a parameter, and

the quantization scale calculation means changes the reference quantization scale for each code amount control unit on the basis of the degree of coding difficulty of each code amount control unit.

8. The moving picture coding apparatus of

claim 4

or

6

wherein

the quantization scale decision function has a reference quantization scale as a parameter, and

the quantization scale calculation means changes the reference quantization scale for each code amount control unit on the basis of a quantization scale of each of the code amount control units which have been already coded.

9. The moving picture coding apparatus of

claim 4

wherein

the quantization scale decision function is made so that the quantization scale varies according to changes in the value of the generated code amount error with respect to the tolerance generated code amount with possessing hysteresis characteristics.

10. The moving picture coding apparatus of

claim 1

comprising:

a code amount control unit changing means for changing the code amount control unit according to a delay time required for decoding of coded data by a decoding apparatus which decodes the coded data output by the moving picture coding apparatus.

11. The moving picture coding apparatus of

claim 2

wherein

the upper limit code amount calculation means changes the upper limit code amount according to a delay time required for decoding of coded data by a decoding apparatus which decodes the coded data output by the moving picture coding apparatus.

12. The moving picture coding apparatus of any of

claims 1

to

11

comprising:

a receiving means for receiving an address of a position of an error which arises in a frame; and

an intra area transition means for successively transitioning a position of an area to be intra-coded in each of predictive coding frames arranged in the video signal in the order of arrangement of the predictive coding frames in the video signal, and when an error arises in coded data in the video signal, transitioning a position of an area to be intra-coded of a subsequent predictive coding frame to a position of the error in the predictive coding frame on the basis of the address from the receiving means.

13. A moving picture coding method for coding a video signal for each block of a prescribed area in a frame and controlling an amount of generated codes in a unit of the frame or a unit which is smaller than the frame comprising steps of:

detecting a cumulative amount of generated codes as a cumulative value of amounts of codes generated from a first block to a block which is being coded in a code amount control unit which is being coded;

calculating a target generated code amount per code amount control unit as a target value of an amount of generated codes per code amount control unit;

calculating a target code amount as a target value of accumulation of amounts of codes generated from the first block to the block which is being coded in the code amount control unit on the basis of the target generated code amount per code amount control unit;

calculating an upper limit code amount as an upper limit value of accumulation of amounts of generated codes per code amount control unit on the basis of the target generated code amount per code amount control unit;

calculating a tolerance generated code amount as a difference between the upper limit code amount and the target code amount;

calculating a generated code amount error as a difference between the cumulative generated code amount and the target code amount; and

obtaining a value of the generated code amount error with respect to the tolerance generated code amount, and calculating a quantization scale of a block which is being coded using a quantization scale decision function whose inclination is changed according to the value of the generated code amount error with respect to the tolerance generated code amount.

14. The moving picture coding method of

claim 13

comprising steps of:

when the cumulative amount of generated codes exceeds the upper limit code amount in a code amount control unit which is being coded, skipping coding of a block in the coding control unit until the cumulative amount of generated codes becomes equal to or smaller than the upper limit code amount; and

when the cumulative amount of generated codes of the coding control unit which has been coded does not reach the target generated code amount per code amount control unit, performing stuffing so that the cumulative amount of generated codes reaches the target generated code amount per code amount control unit.