Single-pass variable bit-rate control for digital video coding

• US 6,192,075 B1
• Filed: 08/21/1997
• Issued: 02/20/2001
• Est. Priority Date: 08/21/1997
• Status: Expired due to Term

• Current Assignee: Integrated Device Technology Incorporated (Renesas Electronics Corporation)
• Original Assignee: Stream Machine Co. (Cirrus Logic Incorporated)
• Inventors: Chen, Cheng-Tie, Huang, Chia-Chun, Jeng, Fure-Ching
• Primary Examiner(s): Kelley, Chris S.
• Assistant Examiner(s): An, Shawn S.
• Application Number:
  US08/918,682
• Time in Patent Office: 1,279 Days
• Field of Search: 348/405, 348/404, 348/403, 348/390
• US Class Current: 375/240
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/14 Coding unit complexity, e.g. amount of activity or edge presence estimation H04N19/146 takes precedence
• CPC Class Codes: H04N 19/149 by estimating the code amount by means of a model, e.g. mathematical model or statistical model
• 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 19/159 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 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/177 the unit being a group of pictures [GOP]
• CPC Class Codes: H04N 19/61 in combination with predictive coding

Abstract

Integrated circuit provides single-pass, real-time digital image encoding by digital signal processor for variable bit rate (VBR) control to improve decoded output quality. Possible peak bit rate range for multiple groups of pictures (GOP) and averaged bit rate limit encoded signal bit rate. Possible bit rate range constraint sets upper/lower range, which is pre-specified or dynamically adapted for current and future GOPs. Signal processor calculates perceptual weighting variable at macroblock level for multiple GOPs, nominal quantization parameters for multiple GOPs, quantization parameter associated at picture level, effective bit rate for each GOP, bit allocation for each picture, and total bit allocation for multiple GOPs. Variable rate signal is recordable in DVD or camcorder device.

Claims

1. In an image processing system for encoding digital video signal, a method for variably controlling signal bit rate to improve video quality, the method comprising the steps of:

receiving a first signal including a plurality of groups of pictures (GOPs), and determining a bit rate constraint comprising a peak bit rate and an averaged bit rate associated with such multiple GOPs; and

processing the first signal to generate therefrom in a single processing pass an encoded second signal having a variable bit rate limited by the bit rate constraint, such multiple GOPs being processed effectively in a look-ahead factor associated with a plurality of GOPs in a specified bit-stream sequence, wherein each of said multiple GOPs comprises at least one I-type picture, said I-type picture delimiting each of said multiple GOP from other GOPs of said multiple GOPs.

2. The method of claim 1 wherein:

the receiving and processing steps are implemented substantially in an integrated circuit.

3. The method of claim 1 wherein:

the encoded second signal is stored in a video recording device.

4. The method of claim 1 wherein:

the bit rate constraint being pre-specified or dynamically re-specified for current or future GOP.

5. The method of claim 1 wherein:

the encoded second signal being limited further by a perceptual weighting variable associated with one or more macroblock associated with one or more GOP.

6. The method of claim 1 further comprising the step of:

determining one or more nominal quantization parameter associated with such multiple GOPs.

7. The method of claim 1 further comprising the step of:

determining one or more quantization parameter associated with one or more picture.

8. The method of claim 1 wherein:

the encoded second signal being limited further by a total bit limit associated with such multiple GOPs.

9. The method of claim 1 further comprising the step of:

determining an effective bit rate associated with one or more GOP.

10. The method of claim 1 further comprising the step of:

determining a bit allocation associated with one or more picture.

11. An integrated digital video processing system comprising:

an MPEG-2 compliant real-time digital image encoding subsystem for receiving an input video signal including a plurality of groups of pictures (GOPs), and generating therefrom, in a single processing pass, an output encoded video signal, such multiple GOPs being processed effectively in a look-ahead factor associated with a plurality of GOPs in a specified bit-stream sequence; and

digital signal processing means coupled to such subsystem for processing the video signal to determine a variable bit rate limited by a bit rate constraint associated with such multiple GOPs, such bit rate constraint comprising a peak bit rate and an averaged bit rate, being pre-specified or dynamically re-specified for one or more current or future GOPs, wherein each of said multiple GOPs comprises at least one I-type picture, said I-type picture delimiting each of said multiple GOP from other GOPs of said multiple GOPs.

12. The system of claim 11 wherein:

the digital signal processing means determines a perceptual weighting variable associated with one or more macroblock associated with such multiple GOPs, one or more nominal quantization parameter associated with such multiple GOPs, one or more quantization parameter associated with one or more picture, an effective bit rate associated with one or more GOP, a bit allocation associated with one or more picture, or a total bit limit associated with such multiple GOPs.

13. The system of claim 11 wherein:

the output encoded video signal is received by a digital video disk (DVD) or camcorder-type device, wherein such signal may be stored in such device.

14. A single-pass variable bit rate controller comprising:

an activity calculator for receiving a signal comprising a plurality of macroblocks including a plurality of groups of pictures (GOPs), and determining an activity measure for each such macroblocks and a bit rate constraint comprising a peak bit rate and an averaged bit rate associated with each such macroblocks; and

a rate controller coupled to the activity calculator for processing the received signal to determine a quantization parameter to provide variably a bit rate according to the bit rate constraints, such multiple GOPs being processed effectively in a look-ahead factor associated with a plurality of GOPs in a specified bit-stream sequence, wherein each of said multiple GOPs comprises at least one I-type picture, said I-type picture delimiting each of said multiple GOP from other GOPs of said multiple GOPs.

15. The controller of claim 14 wherein:

the rate controller further provides a perceptual weighting variable associated with one or more macroblock associated with such GOP, one or more nominal quantization parameter associated with such GOP, one or more quantization parameter associated with one or more picture, an effective bit rate associated with one or more GOP, a bit allocation associated with one or more picture, or a total bit limit associated with such GOP.

16. A process for generating a variable bit rate signal comprising the steps of:

determining a bit rate range for one or more groups of pictures (GOPs) in a digital video bit stream and a bit rate constraint comprising a peak bit rate and an averaged bit rate associated with multiple GOPs; and

generating in a single processing pass according to the bit rate constraint an encoded signal from the digital video bit stream, the encoded signal having a bit rate which is controllable within the bit rate range, such multiple GOPs being processed effectively in a look-ahead factor associated with a plurality of GOPs in a specified bit-stream sequence, wherein each of said multiple GOPs comprises at least one I-type picture, said I-type picture delimiting each of said multiple GOP from other GOPs of said multiple GOPs.