A method of operating a spatial light modulator (120, 520-524, 720) based optical lithography tool (100, 200, 300) for patterning a substrate, the method comprising: defining an area array of pixels on said substrate, the size and configuration of said pixels corresponding to the projected spacing and configuration of individually switchable elements in said spatial light modulator (120, 520-524, 720, 1000); assigning a dose value (1401, 1501, 2101, 2102, 2103, 2104, 2400, 2401, 2402, 2403, 2700, 2701, 2702, 2703, 2704) to each pixel on said substrate (140, 1002), said dose being symmetrical to said pixel and computed from a feature pattern in a design data file; decompressing said dose values for each pixel on said substrate (140, 1002) into a sequence of values representing states for each element of said spatial light modulator for each clock cycle, said elements having at least two states, wherein a first state allows light to reach said substrate and a second state stops light from reaching said substrate; loading said values representing states for each element into a spatial light modulator memory; illuminating said spatial light modulator; projecting an image of said spatial light modulator on said substrate, said projection being implemented by projection optics situated between said spatial light modulator and said substrate; once every clock cycle, switching said elements of said spatial light modulator according to said values in said spatial light modulator memory; and, during each clock cycle, displacing said substrate and said projected image relative to each other by a distance equal to said spacing (1008, 1215) between said pixels, wherein the dose value corresponds to a fractional gray level of exposure less than or equal to a maximum gray level of exposure, and a pixel on said substrate receives, in serial, doses of energy from multiple elements of said spatial light modulator additive to the dose value for the pixel. defining an area array of pixels on said substrate, the size and configuration of said pixels corresponding to the projected spacing and configuration of individually switchable elements in said spatial light modulator (120, 520-524, 720, 1000); assigning a dose value (1401, 1501, 2101, 2102, 2103, 2104, 2400, 2401, 2402, 2403, 2700, 2701, 2702, 2703, 2704) to each pixel on said substrate (140, 1002), said dose being symmetrical to said pixel and computed from a feature pattern in a design data file; decompressing said dose values for each pixel on said substrate (140, 1002) into a sequence of values representing states for each element of said spatial light modulator for each clock cycle, said elements having at least two states, wherein a first state allows light to reach said substrate and a second state stops light from reaching said substrate; loading said values representing states for each element into a spatial light modulator memory; illuminating said spatial light modulator; projecting an image of said spatial light modulator on said substrate, said projection being implemented by projection optics situated between said spatial light modulator and said substrate; once every clock cycle, switching said elements of said spatial light modulator according to said values in said spatial light modulator memory; and, during each clock cycle, displacing said substrate and said projected image relative to each other by a distance equal to said spacing (1008, 1215) between said pixels, wherein the dose value corresponds to a fractional gray level of exposure less than or equal to a maximum gray level of exposure, and a pixel on said substrate receives, in serial, doses of energy from multiple elements of said spatial light modulator additive to the dose value for the pixel.