1. A method of producing an image comprising a plurality of pixels from one or more functions executed and applied to at least some of the plurality of pixels by one or more processing units, the method comprising: evaluating a value of each of the one or more functions for each pixel of the image on the one or more processing units; and determining, on the one or more processing units, at least one of an intensity value and a color value for each pixel by combining two or more of the evaluated values.