An input and/or output unit which reads or records a picture utilizing a scanning beam in which sampling positions of picture elements in a main scanning direction are uniformly spaced. A first clock signal is produced which is at least three times as high in frequency as an output sampling clock signal. The first clock signal operates a counter, the output of which is compared with the output of a ROM. The ROM is addressed by a counter which is incremented by output comparison pulses. The output of the comparator is also utilized as the output sampling signal. Numerical values are stored in the ROM such that the output pulses from the comparator occur at times corresponding to constant sampling intervals of the scanning beam along a scanning line.