The aerial photograph will be computerised (numerised) and submitted to various treatments in order to improve its legibility. Monochrome and colour treatments are dealt with separately. Monochrome pictures will be presented with a method differing from ordinary display, in order to stress their properties. A histogram will supply the display frequency of each level of grey in the picture. This distribution of grey levels will be used to modify the dynamics of negatives and to find the limits of these levels. Pixel modification in relation to its environnement (smoothing) and the use of an arithmetic operator will enhance contrast when the negative is too weak. Computer treatment of colour photographs will call for a completely different method : a range of tints will be created, to be followed by their cycling.