Values at nodes of a LUT which is arranged as a rectangular grid of cells are populated, wherein the populated values model an underlying process that transforms from a first color space to a second color space, and some of the cells of the LUT are completely inside a constraint boundary of the underlying process and some of the cells are not completely inside the constraint boundary. The cells are indexed in a certain order. Samples of the underlying process are accessed. Values of nodes for cells whose nodes are all within the constraint boundary are populated first by using the samples of the underlying process. Values of nodes for cells whose nodes are not all within the constraint boundary are populated second by visiting such cells in the indexed order and populating values for the unpopulated nodes using populated ones of the nodes of such cells and the accessed samples.