Abstract: A spatial light modulator in the form of a deformable mirror device receives from a frame store data which has been formatted by a data formatter subsequent to gamma correction in a ROM look-up table. The DMD displays different light levels by being ON for selected periods of a series of durations 4, 8, 16, - - - , 1024 varying in proportion to a basic period multiplied by powers of two. The shortest duration 4 for which the DMD can be turned on is a multiple of the basic period, and the series includes additional durations 5, 6, and 7 in the series between the shortest displayable duration 4 and the next power of two 8. Durations 1, 2, and 3 of less than the shortest displayable duration can be displayed by adjusting the turn-on time of a proportion of the adjacent mirrors. The longest duration for which the mirror can be turned on can be employed twice.