Image analysis – Image compression or coding – Interframe coding
Reexamination Certificate
1998-03-26
2001-01-16
Couso, Jose L. (Department: 2724)
Image analysis
Image compression or coding
Interframe coding
C382S238000
Reexamination Certificate
active
06175654
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of digital image processing. More specifically, the present invention relates to a method and apparatus for encoding data in an interframe video encoder.
BACKGROUND OF THE INVENTION
Interframe video encoding systems in the past predicted a current frame from a previously reconstructed frame and performed quantization on the residual between the previous frame and the predicted frames on a region-by-region basis. For example, in the Moving Pictures Experts Group 2 (MPEG-2) Video Compression Standard, published 1994, macroblocks of 16×16 pixels are predicted and the residual of the macroblocks are encoded. Due to the structure of the encoded bitstream syntax, the regions are encoded in a sequential fashion starting at the top-left comer of the frame and proceeding in rows across, and then down the frame. If a particular data rate is required for the transmission of the encoded bitstream within a bandlimited channel, data rate control is employed to encode each frame to a specific bit allocation. Accurate control of the encoded frame size is required for low-delay environments because an overshoot in the encoded frame size is buffered, incurring delay.
Prior methods used for frame-accurate data rate control dynamically increased or decreased the degree of lossy encoding for each region of the residual frame to achieve the desired bit allocation. A higher degree of lossy encoding generally resulted in fewer encoded bits. The decision to alter the degree of lossy encoding is performed using feedback of the number of bits spent to encode the first portion of the frame and statistical information on the regions that still need to be encoded.
A problem with these methods is that a frame may be generated with regions of vastly different reconstructed quality where the quality of the region may depend on the sequential order of the region within the frame. For example,
FIG. 1
illustrates a bit map
100
of an image encoded using this prior art method of dynamic quantization. The bit map
100
includes a plurality of macroblocks
101
-
180
. It should be appreciated that any number of macroblocks may be used to compose the bit map
100
and that
80
macroblocks are shown for illustrative purposes only. Due to the structure of the encoded bitstream syntax, the macroblocks are encoded in a sequential fashion starting at the top-left comer of the frame with macroblock
101
and proceeding left to right across each row, and then down the frame, ending with macroblock
180
. If for example, the need to increase the degree of lossy encoding to meet a data rate requirement is realized during the encoding of macroblock
144
, the macroblocks located at the upper regions of the frame, macroblocks
101
-
144
, may have higher reconstructed quality than macroblocks located at the bottom regions of the frame, macroblocks
145
-
180
. The discrepancy in the quality of the image in regions represented by macroblocks
101
-
144
and macroblocks
145
-
180
may be noticeable and undesirable. Another problem with these methods is that additional bits are required to describe the change in degree of lossy encoding for each region in the frame.
SUMMARY
A method for encoding data in an interframe video encoder is disclosed. Regions of a frame to be encoded are ordered according to prediction distortion values. The regions of the frame are encoded according to the ordering.
REFERENCES:
patent: 5778334 (1998-07-01), Ozawa et al.
patent: 5781249 (1998-07-01), Hwang
patent: 5825929 (1998-10-01), Chen et al.
patent: 5909513 (1999-06-01), Liang et al.
Blakely , Sokoloff, Taylor & Zafman LLP
Couso Jose L.
Do Anh Hong
Intel Corporation
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