Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1998-11-05
2003-04-22
Lee, Young (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06553068
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a highly efficient coding method and apparatus used for recording or transmitting picture signals, and more particularly, to a code amount control system that reduces the total code amount of the whole picture to a predetermined value or less, while restraining the deterioration of picture quality.
BACKGROUND ART
An example of this type of picture signal coding method is an interframe coding system represented by MPEG (Moving Picture Experts Group). As code amount control in such a coding system, two types of code amount control, that is, (1) intra-GOP interframe code amount control for one GOP (Group of Pictures) and (2) intraframe inter-macro-block code amount control for one frame, are necessary.
In a TM
5
system widely known as a test model of the MPEG, for the above (1) intra-GOP interframe code amount control, the target code amount for a coding frame is found from the activity of previously encoded frames and the remaining code amount. Here, the remaining code amount means a code amount obtained by subtracting the generated code amount of encoded frames from a code amount assigned to a GOP to which the coding frame belongs, that is, a code amount assigned to frames after the coding frame.
For the above (2) intraframe inter-macro-block code amount control, the quantization parameter for a coding macro block (hereinafter referred to as a scaling factor) is found from the relationship between the generated code amount up to the present time and the target code amount. This system is called a feedback system.
On the contrary, in a feedforward system, which is also well known for the intraframe inter-macro-block code amount control, a code amount is pre-calculated by using all available scaling factors (in the MPEG 2, 31 scaling factors can be used) and the scaling factor that is the closest to the target code amount among the obtained 31 code amounts is selected as the final scaling factor.
The scaling factor is a parameter used in quantization. One scaling factor is provided corresponding to one macro block. When the value of the scaling factor is small, the macro block is quantized in a smaller quantization step. On the contrary, when the value of the scaling factor is large, the macro block is quantized in a larger quantization step.
FIG. 16
shows a block diagram of a picture signal coding device using a conventional intra-GOP interframe code amount control system. In
FIG. 16
,
800
denotes a motion vector detection portion,
801
denotes a differential picture generation portion,
802
denotes an activity calculation portion,
803
denotes a target code amount determination portion,
804
denotes a coding portion,
805
denotes an assigned code amount updating portion, and
806
denotes a local decoder.
A picture signal is inputted to the motion vector detection portion
800
and the differential picture generation portion
801
. When the inputted picture type is a P type or B type picture, the motion vector detection portion
800
detects motion vectors with respect to reference picture(s) stored in the memory and outputs the detected motion vectors. When the inputted picture is an I type picture, the motion vector detection portion
800
does not detect motion vectors. The motion vectors outputted from the motion vector detection portion
800
are inputted to the differential picture generation portion
801
.
When the inputted picture type is a P type or B type picture, the differential picture generation portion
801
generates a predicted picture from the inputted motion vectors and decoded reference picture(s) inputted from the local decoder
806
and calculates the differences between the predicted picture and the inputted picture. The differential picture outputted from the differential picture generation portion
801
is inputted to the coding portion
804
.
If there is a frame that is the same picture type in the previously encoded frames, the target code amount determination portion
803
determines a target code amount from the activity of the encoded frame and the remaining code amount. If there is no frame of the same picture type, the target code amount determination portion
803
sets a specific initial value as the target code amount. The target code amount is inputted to the coding portion
804
.
The coding portion
804
encodes the inputted differential picture by the inputted target code amount and outputs encoded data and an average scaling factor. The encoded data is inputted to the activity calculation portion
802
, the assigned code amount updating portion
805
, and the local decoder
806
. The average scaling factor is inputted to the activity calculation portion
802
.
The activity calculation portion
802
calculates a generated code amount from the inputted encoded data, calculates an activity from the inputted average scaling factor and the calculated generated code amount, and updates the activity of the frame of the same picture type as the coding frame to the calculated activity.
The assigned code amount updating portion
805
calculates a generated code amount from the inputted encoded data and updates the assigned code amount. The local decoder
806
decodes the inputted encoded data and generates a decoded picture.
FIG. 17
shows a block diagram of the coding portion
804
. In
FIG. 17
,
810
denotes a macro-blocking portion,
811
denotes an orthogonal transformation portion,
812
denotes a quantization portion,
813
denotes an importance calculation portion,
814
denotes a scaling factor determination portion, and
815
denotes a variable length coding portion. A conventional intraframe inter-macro-block code amount control system will be described with reference to this figure.
A differential picture inputted to the coding portion is inputted to the macro-blocking portion
810
. The macro-blocking portion
810
performs the process of blocking and macro-blocking the inputted differential picture. The macro-blocked data is inputted to the orthogonal transformation portion
811
and the importance calculation portion
813
.
The orthogonal transformation portion
811
performs orthogonal transformation for each block and outputs transformation coefficients. The transformation coefficients are inputted to the quantization portion
812
. The importance calculation portion
813
calculates an importance for each macro block and outputs the importance data indicating the importance of the macro block.
The importance data is inputted to the scaling factor determination portion
814
. The scaling factor determination portion
814
determines a scaling factor from the importance data of the coding macro block and the remaining code amount. Here, the remaining code amount means a code amount obtained by subtracting the sum of the generated code amounts of macro blocks previously encoded from the target code amount set for the frame, that is, a code amount assigned to the remaining macro blocks including the coding macro block.
The scaling factor outputted from the scaling factor determination portion
814
is inputted to the quantization portion
812
. The quantization portion
812
quantizes the transformation coefficients provided from the orthogonal transformation portion
811
by the inputted scaling factor and outputs quantized data. The quantized data is inputted to the variable length coding portion
815
.
The variable length coding portion
815
performs the variable length coding of the inputted quantized data and outputs encoded data. The encoded data is inputted to the scaling factor determination portion
814
. The scaling factor determination portion
814
calculates the generated code amount of the encoded macro block based on the inputted encoded data and updates the remaining code amount.
FIG. 18
is a block diagram of another configuration of the conventional coding portion
804
. In
FIG. 18
,
820
denotes a macro-blocking portion,
821
denotes an orthogonal transformation portion,
822
denotes a quantization portion,
823
denotes an importance calculation portion
Fujiwara Yuji
Nishino Masakazu
Takeuchi Seiichi
Wake Kazuhiro
Lee Young
Rosenthal & Osha L.L.P.
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