The characterization of light by its tristimulus coordinates is briefly reviewed. The vector-transformation properties of these coordinates are shown, and the interpretation of change of reference stimuli as a change of basis in a 3-dimensional vector space is mentioned. The transformation coefficients are then examined as inner products, in a vector space over a basis of the order of the continuum. In this larger system, all possible sets of tristimulus coordinates are associated with a common 3-dimensional subspace. The vector analogy is thereby extended and a generalization is made from tristimulus coordinates to systems based on any number of arbitrary weighting functions. Each such system has an associated subspace, of the appropriate number of dimensions (not necessarily 3), not necessarily significant for human vision. Applications to spectrum characterization and electro-optical detector–response estimation are given.
© 1966 Optical Society of America
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