1. A device for the dynamic adjustment of a black/white discrimination threshold for the processing of images which are composed of a matrix of pixels which each contain a grey value and which are arranged in rows and columns of the matrix, said device comprising: a. a first input (60) for receiving the grey values; b. a threshold generator (68) which comprises: b1. first means (72, 74) for receiving the grey values of a first sequence of first local sub-sets of pixels and for determining for each first local sub-set a local black/white threshold for presentation on a first output; c. a discriminator (64) for presenting alternatively a black or a white signal on a second output (66) by comparison of the grey value of a pixel with the local black/white threshold applicable to the relevant pixel, characterized in that the threshold generator comprises: b2. an edge detector which comprises a second input which is connected to said first input in order to receive the grey values of a second sequence of second local sub-sets of pixels for the detection of a local edge between darker pixels and lighter pixels, thus forming an accept signal on a third output (82), but forming a reject signal on the third output in the absence of such a local edge; there are also being provided: d. time control means (62) for presenting a black/white signl of a pixel, on the basis of a first local sub-set of pixels to the second output together with the accept/reject signal on the third output which has been generated on the basis of a second local sub-set of pixels associated with said first local sub-set of pixels.