Image analysis – Image compression or coding – Lossless compression
Reexamination Certificate
1998-12-15
2001-05-29
Mancuso, Joseph (Department: 2621)
Image analysis
Image compression or coding
Lossless compression
Reexamination Certificate
active
06240214
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for coding a binary shape signal; and, more particularly, to an adaptive context-based arithmetic coding method and apparatus for enhancing the coding efficiency of the binary shape signal.
DESCRIPTION OF THE PRIOR ART
A binary shape signal, representing the location and shape of an object, can be expressed as a binary alpha block (BAB) of P×Q, e.g., 16×16, binary pixels within a frame or video object plane (VOP), wherein each binary pixel has a binary value, e.g., 0 or 255, representing either a background pixel or an object pixel. A BAB can be encoded by using a conventional bit-map-based shape coding method such as a context-based arithmetic encoding (CAE) method.
For instance, for an intra-frame, a current BAB is encoded by using a conventional intra-CAE technique, wherein each pixel in the current BAB is arithmetically coded based on an intra-context comprised of a set of pixels selected from a current frame. In other words, when encoding the current BAB, pixels from neighboring BAB's are used to make up the intra-context. A border of width
2
around the current BAB is used in order to provide a current bordered BAB as depicted in FIG.
8
. In
FIG. 8
, the pixels in the light area of the current bordered BAB are the part of the current BAB to be encoded and the pixels in the dark area of the current bordered BAB are the border pixels. These are obtained from the neighboring BAB's of the current BAB except for those marked ‘0’ which are unknown at a decoding time. Based on the current bordered BAB, the intra-context is selected as shown in FIG.
7
A. Therefore, in
FIG. 7A
, a shaded pixel, i.e., a pixel in the current BAB, is encoded by using its intra-context
10
comprised of, e.g., C
0
to C
9
.
For an inter-frame, the current BAB may be coded by using either the intra-CAE or an inter-CAE technique depending on whichever CAE technique between the two generates a less amount of encoded data. According to the inter-CAE technique, an error representing a difference between the current BAB and each of predetermined candidate BAB's thereof included in a previous frame is calculated first and a most similar candidate BAB and a motion vector are found by a motion estimation technique, wherein the most similar candidate BAB represents a candidate BAB generating a least error among the candidate BAB's, and the motion vector denotes a displacement between the current BAB and the most similar candidate BAB. Thereafter, each pixel in the current BAB is arithmetically coded based on an inter-context; and a motion vector difference (MVD) which represents a difference between the motion vector and a motion vector predictor (MVP) thereof is encoded by using, e.g., a variable length coding (VLC) scheme. Referring to
FIG. 7B
, the inter-context is composed of two subsets of pixels: a first subset of pixels
20
A includes, e.g., C
0
to C
3
, which are selected from pixels in the current frame in a similar manner that is used in the intra-CAE; and a second subset of pixels
20
B includes, e.g., C
4
to C
8
, which are chosen from the previous frame based on the motion vector. Namely, a border of width
1
around a motion compensated BAB, detected from the previous frame by using the motion vector, is utilized to supply a bordered motion compensated (MC) BAB as described in
FIG. 9
, wherein the light area corresponds to the motion compensated BAB and the dark area corresponds to the border. Once the bordered motion compensated BAB is determined, the second subset of pixels
20
B including the binary pixels C
4
to C
8
is selected from the bordered MC BAB, wherein the pixel position of the pixel C
6
is identical to that of the shaded pixel.
Accordingly, either the intra-context or the inter-context is selected as illustrated above and a context number for each of the pixels in the current BAB is calculated based on its corresponding context. Once the context number for each of the pixels in the current BAB is ciphered, a probability corresponding to the context number is detected from a probability table containing predetermined probabilities assigned to various context numbers and the detected probability is arithmetically encoded to thereby produce an encoded BAB data. For further details of the CAE techniques and the MVD, reference may be made to MPEG-4 Video Verification Model Version 7.0, International Organization for Standardization, Coding of Moving Pictures and Associated Audio Information, ISO/IEC JTC1/SC29/WG11 MPEG97/N1642, Bristol, April 1997.
Although the number of bits to be transmitted is reduced through the use of the conventional CAE technique as discussed above, a large number of bits may still be needed in transmitting the binary shape signal and, therefore, a further reduction in the number of bits used in encoding the binary shape signal is desired.
SUMMARY OF THE INVENTION
It is, therefore, a primary object of the present invention to provide a method and apparatus for encoding a binary shape signal by using an adaptive CAE technique so as to reduce the amount of transmission data.
In accordance with one aspect of the present invention, there is provided a method for encoding a binary shape signal including a plurality of binary pixels, each binary pixel having one of two different binary values, comprising the steps of:
(a) detecting distribution characteristics between the pixels in the binary shape signal to thereby produce a first or a second selection signal;
(b) in response to the first selection signal, encoding the binary shape signal by using a first context-based arithmetic encoding technique for processing the binary shape signal on a pixel-by-pixel basis to thereby generate the encoded binary shape signal; and
(c) under the control of the second selection signal, encoding the binary shape signal by using a second context-based arithmetic encoding technique for processing the binary shape signal on a subblock-by-subblock basis to thereby produce the encoded binary shape signal, wherein the binary shape signal is partitioned into a multiplicity of subblocks and the number of pixels in each subblock is smaller than the number of pixels in the binary shape signal and larger than 1.
In accordance with another aspect of the present invention, there is provided a method for encoding a binary shape signal including a plurality of binary pixels, each binary pixel having one of two different binary values, which comprises the steps of:
(a) encoding the binary shape signal by using a first context-based arithmetic encoding technique for processing the binary shape signal on a pixel-by-pixel basis to thereby generate first encoded data;
(b) encoding the binary shape signal by using a second context-based arithmetic encoding technique for processing the binary shape signal on a subblock-by-subblock basis to thereby produce second encoded data, wherein the binary shape signal is partitioned into a multiplicity of subblocks and the number of pixels in each subblock is smaller than the number of pixels in the binary shape signal and larger than 1;
(c) calculating the numbers of bits of the first and the second encoded data and comparing the calculated bit numbers with each other; and
(d) outputting either the first or the second encoded data as the encoded binary shape signal in conformity to the comparison result in the step (c).
REFERENCES:
patent: 5970164 (1999-10-01), Bamberger et al.
patent: 5999189 (1999-12-01), Kajiya et al.
patent: 6049631 (2000-04-01), Kim
patent: 6094225 (2000-07-01), Han
Bayat Ali
Daewoo Electronics Co. Ltd.
Mancuso Joseph
Pennie & Edmonds LLP
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