Colored Matching Functions for Observers of Arbitrarily Sized Targets

CIE has adopted two basic color matching systems - the first, published in 1931, for observers viewing a two degree target - and the supplementary system, published in 1964, for observers viewing a target of ten degrees subtense. When the target subtends a viewing angle between (or, for that matter, outside) these limits, we are faced with the questions of what color matching function to used and to what degree of approximation are we dealing with? While we know there are small differences between the two and ten degree systems (and, in many cases, can use either with relative impunity), it is not really understood how these functions behave as they approach infinitesimally small targets. A primary purpose of this study, then, is to suggest an extrapolation of these functions to this limit. While we know there are small differences between the two and ten degree systems (and, in many cases, can use either with relative impunity), it is not really understood how these functions behave as they approach infinitesimally small targets. A primary purpose of this study, then, is to suggest an extrapolation of these functions to this limit. A power function of the spectral tristimulus values which has as its limit an exponential function as the viewing angle approaches zero was used for the extrapolation model. The choice of this model is discussed. It was discovered that the two degree system should be adequate for color matching problems of targets less than two degrees subtense.