Apparatus and method for optimizing the rate control in a coding system

• US 6,243,497 B1
• Filed: 02/11/1998
• Issued: 06/05/2001
• Est. Priority Date: 02/12/1997
• Status: Expired due to Term

• Current Assignee: MediaTek, Inc.
• Original Assignee: Sarnoff Corporation (SRI International, Inc.)
• Inventors: Zhang, Ya-Qin, Chiang, Tihao
• Primary Examiner(s): Mancuso, Joseph
• Assistant Examiner(s): Bayat, Ali
• Application Number:
  US09/022,349
• Time in Patent Office: 1,210 Days
• Field of Search: 348/405, 348/390, 348/415, 348/416, 348/699, 348/403, 348/414, 348/417, 348/418, 348/419, 348/397, 358/136, 358/133, 358/105, 382/251, 382/250, 382/238, 382/236, 382/284, 382/294, 382/232
• US Class Current: 382/251
• CPC Class Codes: H04N 19/10 using adaptive coding
• 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 19/129 Scanning of coding units, e.g. zig-zag scan of transform coefficients or flexible macroblock ordering [FMO]
• CPC Class Codes: H04N 19/132 Sampling, masking or truncation of coding units, e.g. adaptive resampling, frame skipping, frame interpolation or high-frequency transform coefficient masking
• CPC Class Codes: H04N 19/146 Data rate or code amount at the encoder output
• CPC Class Codes: H04N 19/147 according to rate distortion criteria rate-distortion as a criterion for motion estimation H04N19/567
• CPC Class Codes: H04N 19/152 by measuring the fullness of the transmission buffer
• CPC Class Codes: H04N 19/154 Measured or subjectively estimated visual quality after decoding, e.g. measurement of distortion use of rate-distortion criteria H04N19/147
• CPC Class Codes: H04N 19/172 the region being a picture, frame or field
• CPC Class Codes: H04N 19/186 the unit being a colour or a chrominance component
• CPC Class Codes: H04N 19/196 being specially adapted for the computation of encoding parameters, e.g. by averaging previously computed encoding parameters processing of motion vectors H04N19/513
• CPC Class Codes: H04N 19/587 involving temporal sub-sampling or interpolation, e.g. decimation or subsequent interpolation of pictures in a video sequence
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/63 using sub-band based transform, e.g. wavelets

Abstract

A method and apparatus for selecting a quantizer scale for each frame to optimize the coding rate is disclosed. A quantizer scale is selected for each frame such that the target bit rate for the frame is achieved while maintaining a uniform visual quality over an entire sequence of frames.

Claims

1. Method for generating a quantizer scale to quantize an image signal having at least one frame, said method comprising the steps of:

(a) computing a distortion measure for a current frame in response to coding information from an immediate previous encoded portion;

(b) computing a target number of bits for encoding said current frame;

(c) computing at least one quantizer scale for said current frame from the computed distortion measure and computed target number of bits in accordance with a complexity measure having a polynomial form, where said polynomial form has at least two distortion measure terms, with each having a different weight; and

(d) applying said computed quantizer scale to quantize said current frame.

2. The method of claim 1, wherein said complexity measure comprises:

3. The method of claim 2, wherein said computed quantizer scale Q is adjusted in accordance with:

4. The method of claim 2, further comprising the steps of:

(e) updating parameters X₁ and X₂ using R_c, where R_c represents an actual number of bits from encoding said current frame using said calculated quantizer scale, Q; and

(f) repeating the steps of (a)-(e) for a next frame of the image signal.

5. The method of claim 2, further comprising the steps of:

(e) updating parameters X₁ and X₂ using a window of information related to a plurality of previously encoded frames; and

(f) repeating the steps of (a)-(e) for a next frame of the image signal.

6. The method of claim 2, wherein said target number of bits, T, is computed in accordance with:

7. The method of claim 6, wherein said target number of bits, T, is adjusted in accordance with:

8. The method of claim 7, wherein said adjusted target number of bits, T′

, is adjusted in accordance with;

9. The method of claim 1, wherein said distortion measure is a mean absolute difference between said current frame and a previous frame.

10. The method of claim 1, wherein said distortion measure is a just noticeable difference (jnd) between said current frame and a previous frame.

11. The method of claim 1, wherein said image signal is a discrete cosine transformed (DCT) of a motion compensated image signal.

12. The method of claim 1, wherein said image signal is a discrete wavelet transformed (DWT) of a motion compensated image signal.

13. Apparatus for generating a quantizer scale to quantize an image signal having at least one frame, said apparatus comprising:

means for computing a distortion measure for a current frame in response to coding information from an immediate previous encoded portion;

means, coupled to said distortion measure computing means, for computing a target number of bits for encoding said current frame;

means, coupled to said distortion measure computing means and said target bit computing means, for computing at least one quantizer scale for said current frame from the computed distortion measure and computed target number of bits in accordance with a complexity measure having a polynomial form, where said polynomia form has at least two distortion measure terms, with each having a different weight; and

means, coupled to said quantizer scale computing means, for quantizing said current frame with said computed quantizer scale.

14. The apparatus of claim 13, wherein said complexity measure comprises:

15. A computer-readable medium 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 comprising of:

(a) computing a distortion measure for a current frame in response to coding information from an immediate previous encoded portion;

(b) computing a target number of bits for encoding said current frame;

(c) computing at least one quantizer scale for said current frame from the computed distortion measure and computed target number of bits in accordance with a complexity measure having a polynomial form, where said polynomial form has at least two distortion measure terms, with each having a different weight; and

(d) applying said computed quantizer scale to quantize said current frame.

16. The computer-readable medium of claim 15, wherein said complexity measure comprises:

17. The computer-readable medium of claim 15, wherein said distortion measure is a mean absolute difference between said current frame and a previous frame.

18. The computer-readable medium of claims 15, wherein said distortion measure is a just noticeable difference (jnd) between said current frame and a previous frame.

19. The computer-readable medium of claim 15, wherein said image signal is a discrete cosine transformed (DCT) of a motion compensated image signal.

20. The computer-readable medium of claim 15, wherein said image signal is a discrete wavelet transformed (DWT) of a motion compensated image signal.

21. Apparatus for encoding an image sequence having at least one input frame, said apparatus comprising:

means for computing a distortion measure for a current frame in response to coding information from an immediate previous encoded portion;

means, coupled to said distortion measure computing means, for computing a target number of bits for encoding said current frame;

means, coupled to said distortion measure computing means and said target bit computing means, for computing at least one quantizer scale for said current frame from the computed distortion measure and computed target number of bits in accordance with a complexity measure having a polynomial form, where said polynomial form has at least two distortion measure terms, with each having a different weight; and

means, coupled to said quantizer scale computing means, for quantizing said current frame with said computed quantizer scale.