Predistortion circuit for video signal coding - supplied from facsimile image scanner and its clock pulse source

The pre-distortion circuit is inserted between an image scanner and a signal coder for run length coding of the binary pulsed facsimile signals, the runs being coded into code-words of the same length. Circuit means are provided for shortening run lengths of exactly 2N image elements or of a whole multiple of this number of image elements to successive runs of one image element. Preferably the last image element of the run of 2N image elements is inverted. The predistortion circuit preferably comprises a buffer register, storing the binary values of the successive image elements, and connected via anti-valence elements to a modulo-N counter, via an inverter. The counter output is connected via a logic circuitry to a delay circuit supplying the coder via a further anti-valence element.