Digitalized television signals of an entire picture field are stored and then are read out with a cross scanning of the lines of the picture field while the next picture field is stored in the memory in the memory cells vacated by cross scanning, thus in a different sequence of memory addresses. The cross scanned digital television signals are then subjected to low-pass filtering to provide output picture point signals at the rate of twice the filter cut-off frequency. If the picture format is to be changed, a sampling rate converter then restores the original sample rate and the digital signals are stored in a second picture field store from which a second cross read-out is made. Where no change of picture format is made the number of lines in the picture is changed in accordance with the setting of the filter cut-off and the related new sampling rate. When the picture format has been changed a vertically compressed picture bordered by black or a vertically expanded picture cut off at top or bottom or both is provided. In the latter two cases a second filtering and restoration of the sample rate is done to provide the same compression or expansion in the horizontal dimension of the picture.