Techniques for low cost gamma mapping convert three-primary input image data, such as RGB data, into a four primary color display color space, such as an RGBW color space, for rendering on the display by calculating a value for W image data based upon the RGB image input data; deriving an allowable value for W based upon a chromaticity specification of the display, and calculating output values for R, G and B image data based upon the allowable W value. A display system receiving input image data specified in three input primary colors includes modules for converting the input image data into image data specifying color values in four display primary colors. A first module determines a value of a first display primary color, and a second module determines the value of second, third and fourth display primary colors by computing a solution set to simultaneous equations based upon the value of the first display primary color.