information in other embodiments color values may be represented in an alternative colorspace or other chromaticity space such as in some embodiments of the present invention a distance metric may be used to determine which model best matches the image illuminant the term u201c distance u201d is usually used to describe a length in space such as the length of a line segment in two or three dimensional space however in this document the term distance may also refer to a similar metric in a space with more than three dimensions the term distance may also refer to a difference between two values that can be represented as points in multi dimensional space a measure d x y is a distance metric iff if and only if it satisfies the following 3 conditions it is usual but often implicit to add the condition of non negativity u2014 i e d x y gt 0 for all x y a distance metric may also be referred to as a difference metric or a dissimilarity metric in this specification and claims the terms distance difference and dissimilarity are synonymous some embodiments of the present invention may perform operations on a subset of the full model set the full model set may be pared down to a subset through an initial selection process final illuminant selection will then take place within the subset of models in other embodiments evaluations can also be performed in greedy fashion the following is an example of greedy evaluation a evaluate a first best guess model.