Method and apparatus for providing intra coding frame bit budget

• US 20060140267A1
• Filed: 12/28/2004
• Published: 06/29/2006
• Est. Priority Date: 12/28/2004
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: General Instrument Corporation (CommScope Holding Company, Inc.)
• Inventors: He, Yong, Wu, Siu-Wai, Chen, Jing Yang
• Granted Patent: US 7,653,129 B2
• Time in Patent Office: Days
• US Class Current: 375/240.30
• CPC Class Codes: H04N 19/103 Selection of coding mode or of prediction mode
• CPC Class Codes: H04N 19/115 Selection of the code volume for a coding unit prior to coding
• CPC Class Codes: H04N 19/124 Quantisation
• CPC Class Codes: H04N 19/152 by measuring the fullness of the transmission buffer
• CPC Class Codes: H04N 19/159 Prediction type, e.g. intra-frame, inter-frame or bidirectional frame prediction
• CPC Class Codes: H04N 19/172 the region being a picture, frame or field
• CPC Class Codes: H04N 19/177 the unit being a group of pictures [GOP]
• CPC Class Codes: H04N 19/51 Motion estimation or motion compensation
• CPC Class Codes: H04N 19/57 Motion estimation characterised by a search window with variable size or shape
• CPC Class Codes: H04N 19/61 in combination with predictive coding

Abstract

The present invention discloses a system and method for adaptive adjustment of bit budget that favors the allocation of bits to intra coding frames (I frames). Namely, an encoder is able to dynamically adjust the bit budget for each picture type in an image sequence, thereby effecting proper usage of the available transmission bandwidth and improving the picture quality. In one embodiment, the present invention will allocate more encoding bandwidth to a current Intra coding frame when the average quantization level of inter coding frames (e.g., P and B frames) of a previous group of pictures is relatively high.

Claims

1. A method for computing a plurality of bit budgets for a plurality of different frame types in a current group of pictures (GOP), where said current GOP comprises at least one of:

an intra coding frame and at least one inter coding frame, comprising;

determining a complexity measure for said intra coding frame and a complexity measure for said at least one inter coding frame;

calculating a bit budget for said intra coding frame and at least one bit budget for said at least one inter coding frame;

obtaining an average quantization level (QL) over inter coding frames in a previous group of pictures (GOP);

determining whether said average quantization level has exceeded a predefined level; and

allocating an additional amount of bits to said bit budget for said intra coding frame if said predefined level has been exceeded.

2. The method of claim 1, further comprising:

reducing said at least one bit budget for said at least one inter coding frame by said additional amount of bits.

3. The method of claim 1,

wherein said at least one inter coding frame comprises at least one P frame and at least one B frame;

and

wherein said at least one bit budget for said inter coding frame comprises at least one P frame bit budget and at least one B frame bit budget.

4. The method of claim 3, wherein said complexity measure (Xi) for said intra coding frame and said complexity measure (Xp, Xb) for said at least one inter coding frame are calculated as follows:

Xi=Si×

Qi;


Xp=Sp×

Qp;


Xb=Sb×

Qb;

where Si, Sp, Sb are actual number of bits generated by encoding a corresponding I, P, or B picture and Qi, Qp and Qb are corresponding average quantization level.

5. The method of claim 3, wherein said bit budget for said intra coding frame and said at least one bit budget for said at least one inter coding frame are calculated as follows:

I frame;

I_target_bitrate=(bit_rate)/(1+(Np*Xp/Xi)+(Nb*Xb/Xi));


P frame;

P_target_bitrate=(bit_rate)/(Np+(Xi/Xp)+(Nb*Xb/Xp));


B frame;

B_target_bitrate=(bit_rate)/(Nb+(Xi/Xb)+(Np*Xp/Xb));

where Np and Nb represent a number of P and B frames in said current GOP, and the bit_rate is a number of bits assigned to said current GOP.

6. The method of claim 3, wherein said allocating said additional amount of bits is performed in accordance with a bias factor α

.

7. The method of claim 6, wherein said bias factor α

is selected as follows;

if ( QL >

     35) α

= 3;

else if (QL >

     25) α

= 2.5;

else if (QL >

     15) α

= 2;

else α

= 1.

8. The method of claim 6, wherein said bit budget for said intra coding frame and said at least one bit budget for said at least one inter coding frame are calculated as follows:

I frame;

I_target_bitrate=(bit_rate)/((Np*Xp/(Xi*α

))+(Nb*Xb/(Xi*α

));


P frame;

P_target_bitrate=(bit_rate)/(Np+(Xi*α

)/Xp+(Nb*Xb/Xp));


B frame;

B_target_bitrate=(bit_rate)/(Nb+(Xi*α

)/Xb+(Np*Xp/Xb));

where Np and Nb represent a number of P and B frames in said current GOP, and the bit_rate is a number of bits assigned to said current GOP.

9. The method of claim 1, wherein said method is implemented in a motion compensated encoder in accordance with a compression standard.

10. The method of claim 9, wherein said compression standard is Moving Picture Experts Group (MPEG)-2.

11. A computer-readable carrier having stored thereon a plurality of instructions, the plurality of instructions including instructions which, when executed by a processor, cause the processor to perform the steps of a method for computing a plurality of bit budgets for a plurality of different frame types in a current group of pictures (GOP), where said current GOP comprises at least one of:

an intra coding frame and at least one inter coding frame, comprising of;

determining a complexity measure for said intra coding frame and a complexity measure for said at least one inter coding frame;

calculating a bit budget for said intra coding frame and at least one bit budget for said at least one inter coding frame;

obtaining an average quantization level (QL) over inter coding frames in a previous group of pictures (GOP);

determining whether said average quantization level has exceeded a predefined level; and

allocating an additional amount of bits to said bit budget for said intra coding frame if said predefined level has been exceeded.

12. The computer-readable carrier of claim 11, further comprising:

reducing said at least one bit budget for said at least one inter coding frame by said additional amount of bits.

13. The computer-readable carrier of claim 11,

wherein said at least one inter coding frame comprises at least one P frame and at least one B frame;

and

wherein said at least one bit budget for said inter coding frame comprises at least one P frame bit budget and at least one B frame bit budget.

14. The computer-readable carrier of claim 13, wherein said complexity measure (Xi) for said intra coding frame and said complexity measure (Xp, Xb) for said at least one inter coding frame are calculated as follows:

Xi=Si×

Qi;


Xp=Sp×

Qp;


Xb=Sb×

Qb;

where Si, Sp, Sb are actual number of bits generated by encoding a corresponding I, P, or B picture and Qi, Qp and Qb are corresponding average quantization level.

15. The computer-readable carrier of claim 13, wherein said bit budget for said intra coding frame and said at least one bit budget for said at least one inter coding frame are calculated as follows:

I frame;

I_target_bitrate=(bit_rate)/(1+(Np*Xp/Xi)+(Nb*Xb/Xi));


P frame;

P_target_bitrate=(bit_rate)/(Np+(Xi/Xp)+(Nb*Xb/Xp));


B frame;

B_target_bitrate=(bit_rate)/(Nb+(Xi/Xb)+(Np*Xp/Xb));

where Np and Nb represent a number of P and B frames in said current GOP, and the bit_rate is a number of bits assigned to said current GOP.

16. The computer-readable carrier of claim 13, wherein said allocating said additional amount of bits is performed in accordance with a bias factor α

.

17. The computer-readable carrier of claim 16, wherein said bias factor α

is selected as follows;

if ( QL >

     35) α

= 3;

else if (QL >

     25) α

= 2.5;

else if (QL >

     15) α

= 2;

else α

= 1.

18. The computer-readable carrier of claim 16, wherein said bit budget for said intra coding frame and said at least one bit budget for said at least one inter coding frame are calculated as follows:

I frame;

I_target_bitrate=(bit_rate)/((Np*Xp/(Xi*α

))+(Nb*Xb/(Xi*α

));


P frame;

P_target_bitrate=(bit_rate)/(Np+(Xi*α

)/Xp+(Nb*Xb/Xp));


B frame;

B_target_bitrate=(bit_rate)/(Nb+(Xi*α

)/Xb+(Np*Xp/Xb));

where Np and Nb represent a number of P and B frames in said current GOP, and the bit_rate is a number of bits assigned to said current GOP.

19. An apparatus for computing a plurality of bit budgets for a plurality of different frame types in a current group of pictures (GOP), where said current GOP comprises at least one of:

an intra coding frame and at least one inter coding frame, comprising;

means for determining a complexity measure for said intra coding frame and a complexity measure for said at least one inter coding frame;

means for calculating a bit budget for said intra coding frame and at least one bit budget for said at least one inter coding frame;

means for obtaining an average quantization level (QL) over inter coding frames in a previous group of pictures (GOP);

means for determining whether said average quantization level has exceeded a predefined level; and

means for allocating an additional amount of bits to said bit budget for said intra coding frame if said predefined level has been exceeded.

20. The apparatus of claim 19, further comprising:

means for reducing said at least one bit budget for said at least one inter coding frame by said additional amount of bits.