Apparatus for adaptive inter-frame predictive encoding of video signal

Abstract

An adaptive predictive encoding apparatus for encoding a video signal by utilizing correlation between frames in both the forward and reverse directions of the time axis. A prediction signal for use in deriving prediction error values to be encoded for a frame is selected by an adaptive prediction section, in units of blocks, from a plurality of mutually differently derived prediction signals, in accordance with the degree of correlation of the block with corresponding ones of a specific preceding independently encoded frame and a specific succeeding independently encoded frame. .Iadd.A complementary adaptive decoding apparatus receives the encoded information and reconstructs the video signal in accordance with information supplied to the adaptive decoding apparatus by the encoding signal. .Iaddend.

What is claimed is: 
     
       1. An adaptive encoding apparatus for encoding an input video signal, said video signal comprising a sequence of frames each comprising successive pixel data the apparatus comprising: encoder means for encoding successive blocks of a frame of said video signal, each of said blocks comprising a fixed-size array of said pixel data values;   means for selecting one in every N of said frames to be transferred directly to said encoder means as a reference frame, to be encoded by intra-frame encoding, where N is a fixed integer of value greater than one; and   adaptive prediction means for executing adaptive prediction processing, as a dependent frame, of each frame occurring between a preceding one and a succeeding one of said reference frames in said frame sequence, by deriving for the data values of each block of a dependent frame respective prediction error values based upon an optimum prediction signal selected from a plurality of prediction signals derived using a plurality of combinations of said preceding and succeeding reference frames.   
     
     
       2. An adaptive predictive encoding apparatus according to claim 1, in which said adaptive prediction means comprises: means for deriving a first prediction signal based on a combination of pixel data of said preceding and succeeding reference frames, a second prediction signal derived only from said preceding reference frame, a third prediction signal derived only from said succeeding, and a non-prediction signal derived only from said dependent frame; and   predictive mode selection means for selecting, for each of said blocks, one out of four prediction modes in which said first, second and third prediction signals and said non-prediction signal are respectively used in deriving predictive error values for respective pixel data of said block, to be sent to said encoder means and encoded thereby, said selection being based upon judgement of said errors, said predictive mode selection means further supplying to said encoding means, to be encoded thereby, predictive mode data indicating predictive modes which have been selected for respective ones of the blocks.   
     
     
       3. An adaptive predictive encoding apparatus according to claim 2, in which said adaptive prediction means further comprises means for varying, in accordance with respective time axis positions of said frames in said video signal, respective weighting values assigned to said preceding and succeeding reference frames for establishing said combination. 
     
     
       4. An adaptive predictive encoding apparatus according to claim 1, and further comprising decoding means for decoding said reference frames after encoding by said encoding means, and for supplying resultant decoded reference frames to said adaptive prediction means for use in producing said prediction signals. 
     
     
       5. An adaptive predictive encoding apparatus according to claim 1, and further comprising an (N-1) frame memory for temporarily storing each dependent frame of said video signal and outputting said each dependent frame to said adaptive prediction means after a fixed delay time, and first and second 1-frame memories for respectively holding pixel data of said preceding and succeeding reference frames and supplying pixel data of said preceding and succeeding reference frames to said adaptive prediction means during adaptive prediction processing of successive ones of said dependent frames. .Iadd. 
     
     
       6.  An adaptive decoding apparatus for decoding a video signal encoded by the apparatus of claim 1, comprising: decoding means for receiving and decoding the encoded reference frames, the prediction error values and a prediction mode signal that identifies which of said plurality of combinations of said preceding and succeeding reference frames were used during encoding to obtain said optimum prediction signal;   prediction signal generating means responsive to the decoded prediction mode signal for reconstructing said optimum prediction signal;   means for combining said prediction error values and said optimum prediction signal for each dependent frame to generate display information corresponding thereto; and   means for outputting the decoded reference frames and the display information for each dependent frame in proper sequence to produce a video signal. .Iaddend. .Iadd.7. A decoding system for decoding video signals that have been encoded in an encoder by arranging said video signals into spaced-apart reference frames and dependent frames located therebetween; said reference frames being output from said encoder in encoded form and used therein to implement one of a plurality of prediction modes for adaptively predicting the display information in each of said dependent frames based upon the degree of correlation between each dependent frame and the reference frames which immediately precede and follow said dependent frame; said encoder thereby generating and outputting therefrom an encoded frame signal for each dependent frame and a prediction mode signal for identifying the prediction mode used to generate said frame signal, said decoding system comprising:   decoding means for receiving and decoding each of the encoded reference frames, and the frame signals and the prediction mode signals associated with each dependent frame;   processing means responsive to said prediction mode signal for reconstructing the display information for each dependent frame from its respective decoded frame signal and the reference frames which precede and follow said dependent frame; and   means for outputting the decoded reference frames and the reconstructed display information generated for each of said dependent frames in proper sequence to produce a video signal. .Iaddend. .Iadd.8. The decoding system in accordance with claim 7, wherein said processing means includes   memory means for storing the two decoded reference frames which respectively precede and follow each dependent frame; and   means responsive to the prediction mode signal for generating and combining weighted values of said display information from said two reference frames to reconstruct the predicted display information for said dependent frame.   
     
     
        .Iaddend. .Iadd.9.  The decoding system in accordance with claim 8, including means for combining said predicted display information with said decoded frame signal to produce an output representing the display information for said dependent frame. .Iaddend. .Iadd.10. The decoding system in accordance with claim 8, wherein said weighted values are generated by multiplying said display information in the preceding reference frame by a first weighting coefficient and said display information in the following reference frame by a second weighting coefficient. .Iaddend. .Iadd.11. The decoding system in accordance with claim 10, wherein, in response to a first prediction mode signal, the first and second weighting coefficients are non-zero. .Iaddend. .Iadd.12. The decoding system in accordance with claim 11 wherein the weighting coefficients are selected such that the reference frame temporally closer to the dependent frame is given a greater weight than the other reference frame. .Iaddend. .Iadd.13. The decoding system in accordance with claim 10, wherein, in response to a second prediction mode signal, the second weighting coefficient is effectively zero. .Iaddend. .Iadd.14. The decoding system in accordance with claim 10, wherein, in response to a third prediction mode signal, the first weighting coefficient is 
     
     
        effectively zero. .Iaddend. .Iadd.15.  The decoding system in accordance with claim 7, wherein, in response to a fourth prediction mode signal, the decoded frame signal is output to represent the display information of said dependent frame. .Iaddend. .Iadd.16. A method for decoding and generating a video signal from video signals that have been encoded in an encoder by arranging said video signals into spaced-apart reference frames and dependent frames located therebetween, said reference frames being output from said encoder in encoded form and used therein to implement one of a plurality of prediction modes for adaptively predicting the display information in each of said dependent frames based upon the degree of correlation between each of said dependent frames and the reference frames which immediately precede and follow each of said dependent frames, said encoder generating and outputting therefrom an encoded frame signal for each of said dependent frames and a prediction mode signal for identifying the prediction mode used to generate said encoded frame signal, said method comprising the steps of: (a) receiving and decoding each of said encoded reference frames, said encoded frame signals and said prediction mode signal associated with each dependent frame;   (b) reconstructing the display information for each dependent frame from the corresponding decoded frame signal and the decoded reference frames which precede and follow said dependent frame in accordance with said associated prediction mode signal; and   (c) outputting the decoded reference frames and the reconstructed display information generated for each of said dependent frames in proper sequence   
     
     
        to generate a video signal. .Iaddend. .Iadd.17.  The method of claim 16 wherein step (b) includes the steps of storing the display information of the two decoded reference frames which respectively precede and follow said dependent frame and combining weighted values of said display information with said decoded frame signal to reconstruct the display information for said dependent frame. .Iaddend. .Iadd.18. The method in accordance with claim 17, wherein said weighted values are generated by multiplying said display information of the preceding reference frame by a first weighting coefficient and said display information in the following reference frame by a second weighting coefficient. .Iaddend. .Iadd.19. The method in accordance with claim 18, wherein, in response to a first prediction mode signal, the first and second weighting coefficients are non-zero. .Iaddend. .Iadd.20. The method in accordance with claim 19, wherein the weighting coefficients are selected such that the reference frame temporally closer to the dependent frame is given a greater weight 
     
     
        than the other reference frame. .Iaddend. .Iadd.21.  The method in accordance with claim 18, wherein, in response to a second prediction mode signal, the second weighting coefficient is effectively zero. .Iaddend. .Iadd.22. The method in accordance with claim 18, wherein, in response to a third prediction mode signal, the first weighting coefficient is effectively zero. .Iaddend. .Iadd.23. The method in accordance with claim 16, wherein, in response to a fourth prediction mode signal, the decoded frame signal is added to a fixed data value to reconstruct the display information of said dependent frame. .Iaddend.