Image analysis – Image compression or coding – Predictive coding
Reexamination Certificate
2000-04-07
2002-05-14
Tran, Phuoo (Department: 2721)
Image analysis
Image compression or coding
Predictive coding
C382S246000
Reexamination Certificate
active
06389173
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a picture encoding and decoding technique, a picture processing technique, a recording technique, and a recording medium and, more particularly, to such techniques and recording medium for use in recording moving picture data onto a recording medium, such as a magneto-optical disc or a magnetic tape, reproducing the recorded data for display on a display system, or transmitting the moving picture data over a transmission channel from a transmitter to a receiver and receiving and displaying the transmitted data by the receiver or editing the received data for recording, as in a teleconferencing system, video telephone system, broadcast equipment, or in a multi-media database retrieving system.
In a system for transmitting moving picture data to a remote place, as in a teleconferencing system or video telephone system, picture data may be encoded (compressed) by exploiting or utilizing line correlation and inter-frame correlation. A high-efficiency encoding system for moving pictures has been proposed by the Moving Picture Experts Group (MPEG). Such system has been proposed as a standard draft after discussions in ISO-1EC/JTC1/SC2/WG11, and is a hybrid system combined from the motion compensation predictive coding and discrete cosine transform (DCT).
In MPEG, several profiles and levels are defined for coping with various types of applications and functions. The most basic is the main profile main level (MOVING PICTURE ML (Main Profile @ at main Level)).
FIG. 1
illustrates a MP@ML encoding unit in an MPEG system. In such encoding unit, picture data to be encoded is supplied to a frame memory
31
for transient storage therein. A motion vector detector
32
reads out picture data stored in the fame memory
31
in terms of a 16×16 pixel macro-block basis so as to detect its motion vector. The motion vector detector
32
processes picture data of each frame as an I-picture, a P-picture, or as a B-picture. Each of the pictures of the sequentially entered frames is processed as one of the I-, P- or B-pictures as a pre-set manner, such as in a sequence of I, B, P, B, P, . . . , B, P. That is, the motion vector detector
32
refers to a pre-set reference frame in a series of pictures stored in the frame memory
31
and detects the motion vector of a macro-block, that is, a small block of 16 pixels by 16 lines of the frame being encoded by pattern matching (block matching) between the macro-block and the reference frame for detecting the motion vector of the macro-block.
In MPEG, there are four picture prediction modes, that is, an intra-coding (intra-frame coding), a forward predictive coding, a backward predictive coding, and a bidirectional predictive-coding. An I-picture is an intra-coded picture, a P-picture is an intra-coded or forward predictive coded or backward predictive coded picture, and a B-picture is an intra-coded, a forward predictive coded, or a bidirectional predictive-coded picture.
Returning to
FIG. 1
, the motion vector detector
32
performs forward prediction on a P-picture to detect its motion vector. The motion vector detector
32
compares prediction error produced by performing forward prediction to, for example, the variance of the macro-block being encoded (macro-block of the P-picture). If the variance of the macro-block is smaller than the prediction error, the intra-coding mode is set as the prediction mode and outputted to a variable length coding (VLC) unit
36
and to a motion compensator
42
. On the other hand, if the prediction error generated by the forward prediction coding is smaller, the motion vector detector
32
sets the forward predictive coding mode as the prediction mode and outputs the set mode to the VLC unit
36
and the motion compensator
42
along with the detected motion vector. Additionally, the motion vector detector
32
performs forward prediction, backward prediction, and bi-directional prediction for a B-picture to detect the respective motion vectors. The motion vector detector
32
detects the smallest prediction error of forward prediction, backward prediction, and bidirectional prediction (referred to herein as minimum prediction error) and compares the minimum prediction error), for example, the variance of the macro-block being encoded (macro-block of the B-picture). If, as a result of such comparison, the variance of the macro-block is smaller than the minimum prediction error, the motion vector detector
32
sets the intra-coding mode as the prediction mode, and outputs the set mode to the VLC unit
36
and the motion compensator
42
. If, on the other hand, the minimum prediction error is smaller, the motion vector detector
32
sets the prediction mode for which the minimum prediction error has been obtained, and outputs the prediction mode thus set to the VLC unit
36
and the motion compensator
42
along with the associated motion vector.
Upon receiving the prediction mode and the motion vector from the motion vector detector
32
, the motion compensator
42
may read out encoded and already locally decoded picture data stored in the frame memory
41
in accordance with the prediction mode and the motion vector and may supply the read-out data as a prediction picture to arithmetic units
33
and
40
. The arithmetic unit
33
also receives the same macro-block as the picture data read out by the motion vector detector
32
from the frame memory
31
and calculates the difference between the macro-block and the prediction picture from the motion compensator
42
. Such difference value is supplies to a discrete cosine transform (DCT) unit
34
.
If only the prediction mode is received from the motion vector detector
32
, that is, if the prediction mode is the intra-coding mode, the motion compensator
42
may not output a prediction picture. In such situation, the arithmetic unit
33
may not perform the above-described processing, but instead may directly output the macro-block read out from the frame memory
31
to the DCT unit
34
. Also, in such situation, the arithmetic unit
40
may perform in a similar manner.
The DCT unit
34
performs DCT processing on the output signal from the arithmetic unit
33
so as to obtain DCT coefficients which are supplied to a quantizer
35
. The quantizer
35
sets a quantization step (quantization scale) in accordance with the data storage quantity in a buffer
37
(data volume stored in the buffer
37
) received as a buffer feedback and quantizes the DCT coefficients from the DCT unit
34
using the quantization step. The quantized DCT coefficients (sometimes referred to herein as quantization coefficients) are supplied to the VLC unit
36
along with the set quantization step.
The VLC unit
36
converts the quantization coefficients supplied from the quantizer
35
into a variable length code, such a Huffman code, in accordance with the quantization step supplied from the quantizer
35
. The resulting converted quantization coefficients are outputted to the buffer
37
. The VLC unit
36
also variable length encodes the quantization step from the quantizer
35
, prediction mode from the motion vector detector
32
, and the motion vector from the motion vector detector
32
, and outputs the encoded data to the buffer
37
. It should be noted that the prediction mode is a mode specifying which of the intra-coding, forward predictive coding, backward predictive coding, or bidirectionally predictive coding has been set.
The buffer
37
transiently stores data from the VLC unit
36
and smooths out the data volume so as to enable smoothed data to be outputted therefrom and supplied to a transmission channel or to be recorded on a recording medium or the like. The buffer
37
may also supply the stored data volume to the quantizer
35
which sets the quantization step in accordance therewith. As such, in the case of impending overflow of the buffer
37
, the quantizer
35
increases the quantization step size so as to decrease the data volume of the quantization coefficients. Conversely, in the cas
Suzuki Teruhiko
Yagasaki Yoichi
Alavi Amir
Frommer William S.
Frommer & Lawrence & Haug LLP
Smid Dennis M.
Tran Phuoo
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