Adaptive prediction encoding device which can effectively refresh an encoded signal with an encoding efficiency kept high

An encoding device for encoding a digital picture signal into an encoded signal, said digital picture signal comprising successive multiframes, each multiframe comprising first through M-th frames, where M represents a plural number, each frame comprising first and second fields, each field comprising a plurality of scanning lines, said device including:

• a predictive encoder responsive to said digital picture signal and a prediction picture signal for predictively encoding said digital picture signal into said encoded signal by using said prediction picture signal;
• a local decoder responsive to said encoded signal and said prediction picture signal for locally decoding said encoded signal into a local decoded signal;
• a first predictor responsive to said local decoded signal for producing a first prediction signal by delaying said local decoded signal by a first delay equal to a first time duration of two successive scanning lines of said digital picture signal;
• a second predictor responsive to said local decoded signal for producing a second prediction signal by delaying said local decoded signal by a second delay equal to a second time duration of said first field of said digital picture signal;
• a third predictor responsive to said local decoded signal for producing a third prediction signal by delaying said local decoded signal by a third delay less than a third time duration of one scanning line of said digital picture signal;
• a comparator for comparing said first through said third prediction signals with said local decoded signal to produce a control signal;
• and a selector responsive to said control signal for selecting one of said first through said third prediction signals as said prediction picture signal;
• said device comprising:
• a first selection forcing circuit connected to said selector and responsive to said digital picture signal for forcing said selector to select said third prediction signal as said prediction picture signal irrespective of said control signal at first timing of fixed scanning lines which periodically appear at a period of (2N+1) scanning lines in each field of said first through said M-th frames of each multiframe of said digital picture signal, where N represents a natural number;
• and
• a second selection forcing circuit connected to said selector and responsive to said digital picture signal for forcing said selector to select said third prediction signal as said prediction picture signal irrespective of said control signal at second timing of additional scanning lines which precede said fixed scanning lines by (m-1) scanning lines in each field of an m-th frame of each multiframe of said digital picture signal, where m consecutively varies from 2 to (2N+1) which is equal to M.