Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1998-01-23
2003-03-18
Kelley, Chris (Department: 2713)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06535558
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
This invention relates to a picture signal encoding method and apparatus, a picture signal decoding method and apparatus and a recording medium, which can be applied with advantage to recording moving picture signals on, for example, a recording medium, such as a magneto-optical disc or a magnetic tape for later reproduction on a display device, transmitting moving picture signals from a transmitting side over a transmission channel for reception and display on the receiving side, as in a teleconferencing system, television telephone system, broadcast equipment or in a multi-media data base retrieval system, or to editing and recording moving picture signals.
2. Description of Related Art
In a system for transmitting moving picture signals to a remote site, such as a teleconferencing system or a television telephone system, the picture signals are compressed by encoding by taking advantage of line-to-line correlation or frame-to-frame correlation.
Among illustrative high efficiency encoding systems for moving picture signals is a so-called MPEG system, which is a system for encoding moving picture signals for storage. This system, discussed by ISO-IEC/JTC1/SC2/WG11 and proposed as a standard draft, employs a hybrid system which is the combination of the motion compensation predictive coding and discrete cosine transform (DCT). In MPEG, a number of profiles and levels are defined for coping with various applications and functions. The most basic is the main profile main level (MP@ML).
Referring to
FIG. 21
, an illustrative structure of an encoder of MP@ML of the MPEG system is explained.
An input picture signal is first entered to a frame memory
201
from which it is subsequently read out and sent to a downstream side circuitry for encoding in a pre-set sequence.
Specifically, picture signals to be encoded are read out on the macro-block basis from a frame memory
201
so as to be entered to a motion vector detection circuit
202
(ME). The motion vector detection circuit
202
processes the picture data of the respective frames as I-, P- or B-pictures, in accordance with a pre-set sequence. It is predetermined by which of the I-, P- or B-pictures the pictures of sequentially entered respective frames are processed. For example, the sequentially entered pictures are processed in the sequence of I, B, P, B, P, . . . , B P.
The motion vector detection circuit
202
refers to a pre-set reference frame to do motion compensation to detect the motion vector. There are three modes for motion compensation (inter-frame prediction), that is forward prediction, backward prediction and bi-directional prediction. The prediction mode for the P-picture is solely the forward prediction, while there are three prediction modes for the B-picture, that is, forward prediction, backward prediction and bi-directional prediction. The motion vector detection circuit
202
selects the prediction mode which minimizes prediction errors and generates the motion vector for the selected mode.
The prediction errors are compared to, for example, the variance values of the macro-block being encoded. If the variance value of the macro-block is smaller, prediction is not executed for the macro-block. Instead, the intra-frame encoding is executed. In this case, the prediction mode is the intra-frame encoding. The information of the motion vector and the prediction mode is entered to a variable length encoding circuit
206
and to a motion compensation circuit
212
(MC circuit).
The motion compensation circuit
212
generates prediction reference picture signals, based on the pre-set motion vector, and sends the prediction reference picture signals to an arithmetic unit
203
. The arithmetic unit
203
finds a difference between the value of the picture signals for encoding, supplied from the frame memory
201
, and the value of the prediction reference picture signals from the motion compensation circuit
212
for each macro-block, and outputs a difference signal to a DCT circuit
204
. In case of the intra-macro-block (macro-block encoded by intra-picture coding), the arithmetic unit
203
directly outputs the macro-block of the picture signals for encoding to the DCT circuit
204
.
The DCT circuit
204
processes the difference signals from the arithmetic unit
203
or the picture signals per se with DCT for conversion into DCT coefficients. These DCT coefficients are entered to a quantization circuit
205
so as to be quantized with a quantization step in meeting with the stored data volume in a transmission buffer
207
(residual data volume that can be stored in a buffer) and so as to be entered as quantized data to the variable length encoding circuit
206
.
The variable length encoding circuit
206
converts the quantized data supplied from the quantization circuit
205
, in accordance with the quantization step (quantization scale) supplied from the quantization circuit
205
into, for example, variable length codes, such as Huffman codes, for outputting the encoded data to the transmission buffer
207
.
The variable length encoding circuit
206
is also fed with the quantization step (quantization scale) from the quantization circuit
205
, the prediction mode (prediction mode indicating which of the intra-picture prediction, forward prediction, backward prediction or bi-directional prediction has been set) from the motion vector detection circuit
202
, and with the motion vector, so as to be encoded with VLC.
The transmission buffer
207
transiently stores the input data and outputs to the quantization circuit
205
data corresponding to the stored data volume as quantization control signals by way of performing buffer feedback. That is, when the data volume stored in the transmission buffer
207
(the residual data volume that can be stored therein) is increased to a theoretical upper limit value, the buffer
207
causes the quantization scale of the quantization circuit
205
to be increased by the quantization control signal to lower the data volume of the quantized data outputted by the quantization circuit
205
. Conversely, should the stored data volume (residual data volume that can be stored) be decreased to an allowable lower limit value, the transmission buffer
207
reduces the quantization scale of the quantization circuit
205
by the quantization control signal to increase the data volume of the quantized data outputted by the quantization circuit
205
. This prevents overflow or underflow of the transmission buffer
207
from occurring.
The encoded data stored in the transmission buffer
207
is read out at a pre-set timing so as to be outputted as a bitstream on the transmission channel.
The quantized data outputted by the quantization circuit
205
is also entered to an inverse quantization circuit (IQ)
208
. This inverse quantization circuit
208
inverse-quantizes the quantized data supplied from the quantization circuit
205
in accordance with the quantization step similarly supplied from the quantization circuit
205
. An output signal of the inverse quantization circuit
208
(DCT coefficients obtained on inverse quantization) are entered to an IDCT circuit
209
, an inverse-quantized output signal of which is sent to an arithmetic unit
210
. If an output signal of the IDCT circuit
209
is a difference signal, the arithmetic unit
210
sums the difference signal from the IDCT circuit
209
to the picture signals from the motion compensation circuit
212
for restoring the picture signals which are then stored in a frame memory
211
. Meanwhile, if the output signal of the IDCT circuit
209
is an intra-macro-block, the output signals of the IDCT circuit
209
(picture signals) are directly outputted. The motion compensation circuit
212
generates prediction reference picture signals using the picture of the frame memory
211
, motion vector and the prediction mode.
Referring to
FIG. 22
, an illustrative structure of the MP@ML decoder of MPEG is explained.
The encoded picture data transmitted over
Suzuki Teruhiko
Yagasaki Yoichi
Frommer William S.
Frommer & Lawrence & Haug LLP
Kelley Chris
Savit Glenn F.
Sony Corporation
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