Television – Bandwidth reduction system – Data rate reduction
Patent
1994-06-28
1995-10-10
Britton, Howard W.
Television
Bandwidth reduction system
Data rate reduction
348409, H04N 736
Patent
active
054574960
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a digital image communication apparatus, and more particularly to encoding and decoding systems for a digital image communication apparatus which transmits and receives signals that are interframe-encoded using leaky prediction.
BACKGROUND ART
Digital transmission of encoded moving-image television signals having a frequency bandwidth of 4 MHz generally requires a transmission rate of about 100 Mbit/s. Since a primary bit rate in a multiplex digital transmission network is of about 1.5 Mbit/s, for example, it is necessary to encode the above television signals highly efficiently in order to transmit the encoded television signals in the multiplex digital transmission network.
A digital image communication apparatus according to the present invention effects interframe encoding for encoding only image changes between frames and transmitting the encoded image information.
FIGS. 1(A) and 1(B) of the accompanying drawings are schematic block diagrams of an overall arrangement of a conventional digital image communication apparatus. FIG. 1(A) shows a transmitter of the conventional digital image communication apparatus, and FIG. 1(B) shows a receiver of the conventional digital image communication apparatus. In the transmitter, a preprocessor 171 converts an input image signal into a digital image signal and filters the image signal, and a next source encoder 172 suppresses the redundancy of the image. A variable-length encoder 173 assigns a code of a short bit length, i.e., a so-called variable-length code, to data which are generated highly frequently. Finally, a multiplexer 174 multiplexes the variable-length code and data such as audio, and outputs the multiplexed data to a network.
The receiver effects a process which a reversal of the process carried out by the transmitter, using a demultiplexer 175, a variable-length decoder 176, a source decoder 177, and a postprocessor 178, and outputs a reproduced image.
The source encoder 172 effects an interframe encoding process for storing a preceding frame (frame), comparing a new present frame with the preceding frame, and encoding only an area where the image has changed, in order to reduce the number of transmitted bits with respect to an area where no image motion occurs in the frame. In this interframe encoding process, since the receiver is supplied with only information representing the difference (predictive error) between the preceding frame and the present frame, if a data error or a data slip (cell loss) occurs even once, then the reproduced image in the receiver is and remains degraded continuously. A leaky prediction process is employed to prevent such a drawback. The leaky prediction process is a process of determining a predictive error after the data of the preceding image is multiplied by a leak coefficient .alpha. (0<a<1). When the leaky prediction process is carried out, the effect of a deterioration of the reproduced image in the past converges to 0 with time for automatic recovery from such a deterioration of the reproduced image.
The internal structures of the source encoder 172 and the source decoder 177 will be described in detail below with reference to FIGS. 2(A) and 2(B) of the accompanying drawings. FIG. 2(A) shows the source encoder 172 and FIG. 2(B) shows the source decoder 177. The source encoder 172 effects a motion compensation leaky prediction process.
In the source encoder 172, a motion vector detector 181 checks each of a plurality of areas of the preceding frame to search for an area which is closest to each of the areas of the present frame, based on the present frame data from the preprocessor 171 and the preceding frame data, and detects the difference between the closest areas of the preceding and present frames as a motion vector. The motion vector is outputted to the variable-length encoder 173 and a memory 182. The memory 182 stores the data of each area of the preceding frame. The data of the area of the preceding image which is associated with the area of the
REFERENCES:
patent: 5128756 (1992-07-01), Johnston et al.
patent: 5218435 (1993-06-01), Lim et al.
patent: 5305102 (1994-04-01), Knaur et al.
Hamano Takashi
Matsuda Kiichi
Sakai Kiyoshi
Au A.
Britton Howard W.
Fujitsu Limited
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