Television system for transmitting digitized television pictures from a transmitter to a receiver where different transform coding techniques are selected on the determination of motion

An encoder for encoding a plurality of television pictures into a digital signal wherein each of said television pictures is formed by two fields and wherein each of said television pictures comprises a plurality of picture pixel blocks which in turn each comprise two field pixel blocks, said encoder comprising:

• a) motion detection means for detecting an indication of motion occurring within a picture pixel block wherein said motion detection means further comprises means for determining whether a detected indication of motion is due to actual motion occurring within said picture pixel block in which case a motion detection signal is generated by said motion detection means, or to a transition in luminance within said picture pixel block without significant actual motion in which case said motion detection signal is not generated;
• b) means, coupled to said motion detection means, for subjecting said picture pixel block to an intraframe transform operation so as to form a plurality of frame coefficients and for subjecting each field pixel block of said picture pixel block to an intrafield transform operation so as to form a plurality of field coefficients;
• and
• c) means, coupled to said motion detection means, for coding and transmitting said frame coefficients as said digital signal if said motion signal is not generated by said motion detection means and for coding and transmitting said field coefficients as said digital signal if said motion signal is generated by said motion detection means.