Television – Bandwidth reduction system – Data rate reduction
Reissue Patent
1994-08-31
2001-03-13
Britton, Howard (Department: 2713)
Television
Bandwidth reduction system
Data rate reduction
C348S400100, C348S405100, C348S416100, C348S420100
Reissue Patent
active
RE037091
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to a television system and more particularly to a motion compensated prediction interframe system for performing motion compensated prediction interframe coding of television signals.
2. Description of the Related Art
Recently, with advance in techniques of moving picture coding, a motion compensated prediction interframe coding system has been developed as an efficient coding system for effecting an efficient coding of a color moving picture for use in a visual telephone (or video telephone), a video conference system, CD ROM, a digital video tape recorder (VTR) and so on. An example of a motion compensated prediction interframe coding system is described in T. Fukinuki: Multidimensional Signal Processing of TV Picture, Nikkan Kogyo Shinbun Company, Chapter 7 “Efficient Coding”, pp. 213-291 (1988. 11. 15).
When a large quantity of prediction error signals is generated, the motion compensated prediction interframe coding system limits an amount of codes of the generated prediction error signals by employing a large step size for quantization (hereunder sometimes referred to as a quantization step size) in such a way that at the coding of a picture can be achieved a constant frame rate. An example of a conventional method of determining a step size for quantization is disclosed in CCITT (Comite Consultatif Internationale Telegraphique et Telephinque) SGXV Document #525: Description of Ref. Model 8 (RM 8), Working Party XV/4 Specialist Group on Coding for Visual Telephony (1989. 6. 9).
Hereinafter, a prior art motion compensated prediction interframe coding system will be describe by referring to FIG.
1
.
In this figure, reference numeral
51
represents an input terminal from which television signals are inputted to the system;
53
a motion vector calculating portion for comparing a picture signal of a block (hereunder referred to as a coding block), which is to be coded, of a current frame with a reproduced picture signal of a previous frame and calculating a motion vector;
54
a picture memory portion for storing reproduced picture signals of a current and previous frames;
58
a motion compensation predicting portion for performing a motion compensation predicting of the reproduced picture signals of the pervious frame;
60
a coding method selection portion for selecting a method of coding of a block from an interframe coding and intraframe coding methods;
62
an intra-loop filter portion for performing two-dimensional lowpass filtering processing of a motion compensation predicting signal;
64
a prediction error evaluating portion for evaluating a prediction error by computing the difference between an original picture signal and a predictive signal of a coding block;
66
a switch portion for selecting a signal, of which an orthogonal transform is effected, in accordance with a coding method selecting signal and further selecting a signal from which a reproduced picture is calculated;
68
an orthogonal transform portion for performing an orthogonal transform of the selected signal;
70
a quantization portion for quantizing coefficients of an orthogonal transform (hereunder referred to as orthogonal transform coefficients) of the selected signal;
73
a quantization step-size computing portion for computing a step size for the quantization;
74
a code memory portion for temporarily storing a transmission frame;
76
an inverse orthogonal transform portion for effecting an inverse orthogonal transform of the quantized coefficients of the orthogonal transform;
78
a reproduced picture calculating portion for calculating a reproduced picture of a current frame;
82
a prediction error coding portion for performing what is called “transmitting channel coding” of a prediction error;
84
a motion vector coding portion for performing the transmitting channel coding of a motion vector;
86
a multiplexer portion for computing a transmitting frame on the basis of the prediction code and the motion vector; and
89
an output terminal from which a transmission signal is output.
Hereinafter, an operation of the prior art motion compensated prediction interframe coding system having the above described arrangement will be described.
First, television signals are converted into digital television signals by an analog-to-digital (A/D) conversion circuit (not shown). Then, pixels represented by the digital television signals are divided into blocks each of which is a rectangular array composed of M×N pixels arranged in M columns and N rows. Further, the digital television signals are input to the system from the input terminal
51
as input television signals
52
. Then, the motion vector calculating portion
53
compares the input television signal with a reproduced picture signal
55
of a previous frame stored in the picture memory portion
54
and calculating the motion of a coding block as a motion vector and moreover outputs a motion vector signal
56
representing the motion vector. Simultaneously, the motion vector calculating portion
53
judges from the result of the evaluation of the motion vector whether the motion compensation made with respect to the coding block is effective or ineffective. Further, the motion vector calculating portion
53
outputs a motion compensation control signal which represents the result of the judgement and is superposed on the motion vector signal
56
.
The motion compensation prediction portion
58
performs a motion compensation prediction of the reproduced television signal
55
of a previous frame in case where the motion compensation control signal indicates that the motion compensation prediction is effective and outputs the reproduced television signal without change as a motion compensation prediction signal
59
in case where the motion compensation control signal indicates that the motion compensation prediction is ineffective.
The coding method selection portion
60
compares the input television signal
52
with the motion compensation prediction signal
59
every block and judges whether or not the motion compensation prediction is effective. Further, the coding method selection portion
60
judges that an intraframe coding method is effective for a current block in question in case where the motion compensation prediction is effective and that an interframe coding method is effective for a current block in question in case where the motion compensation prediction is not effective, and outputs a coding method selection signal
61
representing the result of this judgement. In this way, a coding method to be used in coding each block may be changed from the intraframe coding method to the interframe coding method and vice versa. This can make the following improvements on another conventional system which employs only the interframe coding method:
(1) Picture quality can be improved after a scene is changed because the intraframe coding method is employed when the scene is changed.
(2) Picture quality can be also improved when a moving body largely moves because a background which has hid itself behind the moving body emerges from behind it and in such a case, the intraframe coding is employed.
Incidentally, in case of a coding method employed in storage type media such as CD ROM, it is necessary to insert a frame of which all blocks are coded by performing the intraframe coding method (hereunder referred to as a refreshment frame) between frames every constant frame period in order to realize an editing function and a backward editing function of a reproduced picture. Further, the insertion of the refreshment frame can be achieved by providing the motion compensation prediction interframe coding system with the intraframe coding function.
Then, the intra-loop filtering portion
62
performs the two-dimensional lowpass filtering processing of a coding block of which the motion compensation prediction is effected by using the motion vector and further outputs a prediction signal
63
. Subsequently, the prediction error evaluating
Fujikawa Wataru
Inoue Ikuo
Matsuya Satoshi
Nagata Atsushi
Tanaka Akiyoshi
Britton Howard
Lowe Hauptman Gopstein Gilman & Berner
Matsushita Electric - Industrial Co., Ltd.
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