Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1999-06-17
2002-06-04
Kelley, Chris (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240110
Reexamination Certificate
active
06400768
ABSTRACT:
BACKGROUND OF THE INVENTION
In general, the present invention relates to a picture encoding apparatus, a picture encoding method, a picture decoding apparatus, a picture decoding method and a presentation medium. More particularly, the present invention relates to a good picture encoding apparatus, a good picture encoding method, a good picture decoding apparatus, a good picture decoding method and a good presentation medium typically used for recording moving-picture data onto an optical magnetic disc or a magnetic tape, playing back the recorded data and displaying the reproduced data on a display as well as used for transmitting moving-picture data from a transmitter side to a receiver side by way of a transmission line, displaying, editing and recording the received moving-picture data on the receiver side in systems such as a television conference system, a television telephone system, broadcasting equipment and a multimedia data-base search system.
In a system for transmitting moving-picture data to a remote destination, such as a television conference system or a television telephone system, the moving-picture data is subjected to a compression-encoding process by taking advantage of line correlation or interframe correlation in order to allow the transmission to be utilized a high degree of efficiency.
As a representative high-performance system for encoding a moving picture, there is provided an MPEG (Moving Picture Experts Group) system which is a kind of cumulative moving-picture encoding technique. The MPEG system is proposed as a standard system, as a result of discussions by an ISO-IEC/JTC1/SC2/WG11. The MPEG system adopts a hybrid method combining a motion-compensation predicting/encoding technique and a DCT (Discrete Cosine Transform) encoding technique.
In the MPEG system, some profiles and levels are defined in order to keep up with a variety of applications and functions. The most basic one is a so-called main profile main level (MP@ML (Main Profile at Main Level).
FIG. 53
is a block diagram showing a typical configuration of an MP@ML encoder of the MPEG system.
Picture data to be encoded is supplied to a frame memory
31
to be temporarily stored therein. A motion-vector detector
32
reads out the picture data stored in the frame memory
31
in macroblock units each composed of typically 16 pixels×16 pixels and detects motion vectors thereof.
The motion-vector detector
32
processes picture data of each frame as an I-picture (in an intraframe encoding process), a P-picture (in a forward-prediction encoding process) of a B-picture (in a bidirectional-prediction encoding process). It should be noted that pictures of frames sequentially supplied to the motion-vector detector
32
are processed as an I, P or B-picture in an order determined in advance. For example, the frames are processed in the order of I, B, P, B, P, - - - , B and P-pictures, for example.
To put it in detail, the motion-vector detector
32
refers to a predetermined reference frame set in advance in the picture data stored in the frame memory
31
and detects a motion vector of a macroblock of the reference frame and a frame being encoded currently by carrying out a pattern matching process (a block matching process) on a small block which is the macroblock with dimensions of 16 pixels×16 lines.
The MPEG system has four picture-prediction modes, namely, an intra- encoding mode (an intraframe encoding mode), a forward-prediction encoding mode, a backward-prediction encoding mode and a bidirectional-prediction encoding mode. An I-picture is encoded in the intra-encoding mode and a P-picture is encoded either in the intra-encoding mode or the forward-prediction encoding mode. A B-picture is encoded in either one of the intra-encoding mode, the forward-prediction encoding mode, the backward-prediction encoding mode and the bidirectional-prediction encoding mode.
That is to say, the motion-vector detector 32 sets the intra-encoding mode as a prediction mode for an I-picture. In this case, the motion-vector detector
32
does not detect a motion vector. Instead, the motion-vector detector
32
supplies information indicating the prediction mode (that is, the intra-encoding mode in this case) to a VLC (Variable-Length Coder) unit
36
and a motion compensator
42
.
In the case of a P-picture, the motion-vector detector
32
carries out forward prediction on the picture to detect a motion vector thereof. Furthermore, the motion-vector detector
32
compares a prediction error obtained as a result of the forward prediction with, for example, a variance of a macroblock being encoded. If the comparison indicates that the variance of the macroblock is smaller than the prediction error, the motion-vector detector
32
sets the intra-encoding mode as a prediction mode and supplies information indicating the intra-encoding mode to the VLC unit
36
and the motion compensator
42
. If the comparison indicates that the prediction error obtained as a result of the comparison is smaller than the variance of the macroblock, on the other hand, the motion-vector detector
32
sets the forward-prediction encoding mode as a prediction mode and supplies information indicating the forward-prediction encoding mode to the VLC unit
36
and the motion compensator
42
along with a detected motion vector.
In the case of a B-picture, the motion-vector detector
32
carries out forward, backward and bidirectional predictions on the picture to detect a motion vector thereof. Furthermore, the motion-vector detector
32
detects the smallest one among prediction errors resulting from the forward, backward and bidirectional predictions and compares the smallest prediction error thus detected (which is referred to hereafter also as a minimum prediction error for the sake of convenience) with, for example, a variance of a macroblock being encoded. If the comparison indicates that the variance of the macroblock is smaller than the smallest prediction error, the motion-vector detector
32
sets the intra-encoding mode as a prediction mode and supplies information indicating the intra-encoding mode to the VLC unit
36
and the motion compensator
42
. If the comparison indicates that the minimum prediction error is smaller than the variance of the macroblock, on the other hand, the motion-vector detector
32
sets an encoding mode producing the minimum prediction error as a prediction mode and supplies information indicating the set prediction mode to the VLC unit
36
and the motion compensator
42
along with a detected motion vector.
Receiving the prediction mode and the detected motion vector from the motion-vector detector
32
, the motion compensator
42
reads out picture data from a frame. memory
41
and supplies the picture data to processors
33
and
40
. It should be noted that the picture data stored in the frame memory
41
to be read out by the motion compensator
42
has been encoded and then decoded back locally in the MP@ML encoder.
The processor
33
reads out the macroblock from the frame memory
31
and computes a difference between the macroblock and a predicted picture received from the motion compensator
42
. The processor
33
then supplies the difference to a DCT unit
34
. It should be noted that the macroblock is a macroblock of the picture data read out by the motion-vector detector
32
from the frame memory
31
.
If the motion-compensator
42
receives only information on a prediction mode from the motion-vector detector
32
, that is, if the intraframe-encoding mode is set as a prediction mode, on the other hand, no prediction picture is output. In this case, the processor
33
(and the processor
40
) does not carry out any processing in particular, merely passing on a macroblock read out from the frame memory
31
to the DCT unit
34
as it is.
In the DCT unit
34
, the data output by the processor
33
is subjected to DCT processing. A DCT coefficient obtained as a result of the DCT processing is supplied to the quantizer
35
. In the quantizer
35
, a quanti
Nagumo Takefumi
Suzuki Teruhiko
Yagasaki Yoichi
Bugg George A
Frommer William S.
Frommer & Lawrence & Haug LLP
Kelley Chris
Sony Corporation
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