Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
2002-04-24
2003-03-18
Lee, Richard (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06535559
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an image encoder, an image encoding method, an image decoder, an image decoding method, and distribution media. More particularly, the invention relates to an image encoder, an image encoding method, an image decoder, an image decoding method, and distribution media suitable for use, for example, in the case where dynamic image data is recorded on storage media, such as a magneto-optical disk, magnetic tape, etc., and also the recorded data is regenerated and displayed on a display, or in the case where dynamic image data is transmitted from a transmitter side to a receiver side through a transmission path and, on the receiver side, the received dynamic image data is displayed or it is edited and recorded, as in videoconference systems, videophone systems, broadcasting equipment, and multimedia data base retrieval systems.
BACKGROUND ART
For instance, as in videoconference systems and videophone systems, in systems which transmit dynamic image data to a remote place, image data is compressed and encoded by taking advantage of the line correlation and interframe correlation in order to take efficient advantage of transmission paths.
As a representative high-efficient dynamic image encoding system, there is a dynamic image encoding system for storage media, based on Moving Picture Experts Group (MPEG) standard. This MPEG standard has been discussed by the International Organization for Standardization (ISO)-IEC/JTC1/SC2/WG11 and has been proposed as a proposal for standard. The MPEG standard has adopted a hybrid system using a combination of motion compensative predictive coding and discrete cosine transform (DCT) coding.
The MPEG standard defines some profiles and levels in order to support a wide range of applications and functions. The MPEG standard is primarily based on Main Profile at Main level (MP@ML).
FIG. 1
illustrates the constitution example of an MP@ML encoder in the MPEG standard system.
Image data to be encoded is input to frame memory
31
and stored temporarily. A motion vector detector
32
reads out image data stored in the frame memory
31
, for example, at a macroblock unit constituted by 16 (16 pixels, and detects the motion vectors.
Here, the motion vector detector
32
processes the image data of each frame as any one of an intracoded picture (I-picture), a forward predictive-coded picture (P-picture), or a bidirectionally predictive-coded picture (B-picture). Note that how images of frames input in sequence are processed as I-, P-, and B-pictures has been predetermined (e.g., images are processed as I-picture, B-picture, P-picture, B-picture, P-picture, . . . , B-picture, and P-picture in the recited order).
That is, in the motion vector detector
32
, reference is made to a predetermined reference frame in the image data stored in the frame memory
31
, and a small block of 16 pixels (16 lines (macroblock) in the current frame to be encoded is matched with a set of blocks of the same size in the reference frame. With block matching, the motion vector of the macroblock is detected.
Here, in the MPEG standard, predictive modes for an image include four kinds: intracoding, forward predictive coding, backward predictive coding, and bidirectionally predictive coding. An I-picture is encoded by intracoding. A P-picture is encoded by either intracoding or forward predictive coding. A B-picture is encoded by either intracoding, forward predictive coding, backward predictive coding, or bidirectionally predictive coding.
That is, the motion vector detector
32
sets the intracoding mode to an I-picture as a predictive mode. In this case, the motion vector detector
32
outputs the predictive mode (intracoding mode) to a variable word length coding (VLC) unit
36
and a motion compensator
42
without detecting the motion vector.
The motion vector detector
32
also performs forward prediction for a P-picture and detects the motion vector. Furthermore, in the motion vector detector
32
, a prediction error caused by performing forward prediction is compared with dispersion, for example, of macroblocks to be encoded (macroblocks in the P-picture). As a result of the comparison, when the dispersion of the macroblocks is smaller than the prediction error, the motion vector detector
32
sets an intracoding mode as the predictive mode and outputs it to the VLC unit
36
and motion compensator
42
. Also, if the prediction error caused by performing forward prediction is smaller, the motion vector detector
32
sets a forward predictive coding mode as the predictive-mode. The forward predictive coding mode, along with the detected motion vector, is output to the VLC unit
36
and motion compensator
42
.
The motion vector detector
32
further performs forward prediction, backward prediction, and bidirectional prediction for a B-picture and detects the respective motion vectors. Then, the motion vector detector
32
detects the minimum error from among the prediction errors in the forward prediction, backward prediction, and bidirectional prediction (hereinafter referred to the minimum prediction error as needed), and compares the minimum prediction error with dispersion, for example, of macroblocks to be encoded (macroblocks in the B-picture). As a result of the comparison, when the dispersion of the macroblocks is smaller than the minimum prediction error, the motion vector detector
32
sets an intracoding mode as the predictive mode and outputs it to the VLC unit
36
and motion compensator
42
. Also, if the minimum prediction error is smaller, the motion vector detector
32
sets as the predictive mode a predictive mode in which the minimum prediction error was obtained. The predictive mode, along with the corresponding motion vector, is output to the VLC unit
36
and motion compensator
42
.
If the motion compensator
42
receives both the predictive mode and the motion vector from the motion vector detector
32
, the motion compensator
42
will read out the coded and previously locally decoded image data stored in the frame memory
41
in accordance with the received predictive mode and motion vector. This read image data is supplied to arithmetic units
33
and
40
as predicted image data.
The arithmetic unit
33
reads from the frame memory
31
the same macroblock as the image data read out from the frame memory
31
by the motion vector detector
32
, and computes the difference between the macroblock and the predicted image which was supplied from the motion compensator
42
. This differential value is supplied to a DCT unit
34
.
On the other hand, in the case where a predictive mode alone is received from the motion vector detector
32
, i.e., the case where a predictive mode is an intracoding mode, the motion compensator
42
does not output a predicted image. In this case, the arithmetic unit
33
(the arithmetic unit
40
as well) outputs to the DCT unit
34
the macroblock read out from the frame memory
31
without processing it.
In the DCT unit
34
, DCT is applied to the output data of the arithmetic unit
33
, and the resultant DCT coefficients are supplied to a quantizer
35
. In the quantizer
35
, a quantization step (quantization scale) is set in correspondence to the data storage quantity of the buffer
37
(which is the quantity of the data stored in a buffer
37
) (buffer feedback). In the quantization step, the DCT coefficients from the DCT unit
34
are quantized. The quantized DCT coefficients (hereinafter referred to as quantized coefficients as needed), along with the set quantization step, are supplied to the VLC unit
36
.
In the VLC unit
36
, the quantized coefficients supplied by the quantizer
35
are transformed to variable word length codes such as Huffman codes and output to the buffer
37
. Furthermore, in the VLC unit
36
, the quantization step from the quantizer
35
is encoded by variable word length coding, and likewise the predictive mode (indicating either intracoding (image predictive intracoding), forward predictive coding, backward predictive coding
Suzuki Teruhiko
Yagasaki Yoichi
Frommer William S.
Frommer & Lawrence & Haug LLP
Gordon Kessler
Lee Richard
Sony Corporation
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