In a television system a digital picture signal is subjected to a transform coding for the purpose of bit rate reduction. In order to detect motion effects between the two fields of a picture, these fields are also examined in a motion detector 8310. If no motion is detected, intraframe transform is employed and if motion is detected intrafield transform is employed. Small motion effects can be eliminated by subjecting the picture signal to a median filtering before subjecting it to an intraframe transform