A photosensitive area 11, such as a photolithographic sheet, in an images plane is notionally subdivided in both dimensions to form contiguous (tiled) sub-areas. Variable illumination means 1,4 provides a selected pixellated light pattern, which is directed 8, 9, 10 to fill a selected one of the sub-areas so that pixels of said pattern are, at least 15 microns across at the sub-area, and control means are responsive to an input signal representative of an image conjointly to control the production and direction of the pixellated patterns so that an entire image is produced over all of the said sub-areas. As shown, the variable illumination means comprises a light source 2 with digital micro-mirror array deflector device 4, and the sub-area is selected by lens array 8 with a shutter 10 and polariser array 11. The latter may be replaced by a two-axis steering mirror and lens array. An analogue micro-mirror array, optionally with, a kaleidoscope, may be used in the illumination means, with (a) collimating optics and lens array; or (b) a focussing macro-lens, for sub-area selection.