1. A machine-implemented method of producing image data from compressed source data, comprising: accessing compressed source data pertaining to an image; interpreting the compressed source data to produce a set of representative colors and modulation data; interpreting portions of the modulation data as a plurality of vectors, each pertaining to a respective region of the image and each region of the image respectively having multiple portions, each of which comprises multiple elements of the image, and as vector modifier data; determining a respective color for each element within a first portion of the region that is to be constructed, based on the set of representative colors, combined according to a selected vector of the plurality of vectors; and determining a respective color for each element within other portions of the region by using the respective vector modifier data associated with that portion to select a vector from the plurality of vectors, to modify that selected vector according to the vector modifier data, and then to combine one or more colors in the set of representative colors, according to the modified selected vector, to produce the colors for the elements in that portion of the region.