Adaptive quantization

• US 5,650,860 A
• Filed: 12/26/1995
• Issued: 07/22/1997
• Est. Priority Date: 12/26/1995
• Status: Expired due to Term

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: C-Cube Corporation (Broadcom, Inc.)
• Inventors: Uz, K. Metin
• Primary Examiner(s): Mancuso, Joseph
• Assistant Examiner(s): Grant, II, Jerome
• Application Number:
  US08/578,815
• Time in Patent Office: 574 Days
• Field of Search: 348/390, 348/420, 348/409, 348/416, 348/405, 348/430, 348/413, 348/414, 348/417, 348/418, 382/236, 358/430, 364/514 R
• US Class Current: 382/253
• CPC Class Codes: H04N 19/107 between spatial and temporal predictive coding, e.g. picture refresh
• CPC Class Codes: H04N 19/124 Quantisation
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/142 Detection of scene cut or scene change
• 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 19/149 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 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/30 using hierarchical techniques, e.g. scalability H04N19/63 takes precedence
• CPC Class Codes: H04N 19/61 in combination with predictive coding

Abstract

A rate control algorithm for an MPEG-2 compliant encoder is described. The rate control algorithm has embodiments useful for constant bit rate and variable bit rate encoding. In particular, the invention relates to adaptive quantization.

Claims

1. In an encoder for encoding an input sequence of interlaced video frames to generate a compressed bitstream, a method for generating a quantization scale factor for coding a macroblock in a frame, said method comprising the steps of:

(1) maintaining by said encoder first, second and third virtual buffers for I, P and B frames in said sequence of frames,

(2) determining by said encoder for a macroblock n in a frame, a rate control quantization scale factor Q_n^R, said rate control quantization scale factor being determined as a function of a ratio of virtual buffer fullness to virtual buffer size for the virtual buffer of the frame to which the macroblock belongs,

(3) multiplying the rate control quantization scale factor for the macroblock by a masking activity quantization scale factor QS_n given by

space="preserve" listing-type="equation">(α

(ma.sub.n +k.sub.1)+ma/[ma.sub.n +α

(ma.sub.n +k.sub.1))

where ma_n is a masking activity for the macroblock,

where ma is a masking activity for the entire picture,

where α and

k₁ are constants,

(4) coding said macroblock in said encoder using said final quantization scale factor to generate a portion of said compressed bitstream.