The von Kries chromatic adaptation method is a technique that is sometimes used in camera image processing. The method is to apply a gain to each of the human
cone cell spectral sensitivity responses so as to keep the adapted appearance of the reference white constant. The application of
Johannes von Kries's idea of adaptive gains on the three
cone cell types was first explicitly applied to the problem of color constancy by
Herbert E. Ives, and the method is sometimes referred to as the Ives transform or the von Kries–Ives adaptation. The
von Kries coefficient rule rests on the assumption that
color constancy is achieved by individually adapting the gains of the three cone responses, the gains depending on the sensory context, that is, the color history and surround. Thus, the cone responses c' from two radiant spectra can be matched by appropriate choice of diagonal adaptation matrices
D1 and
D2: :c'=D_1\,S^T\,f_1 = D_2\,S^T\,f_2 where S is the
cone sensitivity matrix and f is the spectrum of the conditioning stimulus. This leads to the
von Kries transform for chromatic adaptation in
LMS color space (responses of long-, medium-, and short-wavelength cone response space): :D = D_1^{-1} D_2=\begin{bmatrix} L_2/L_1 & 0 & 0 \\ 0 & M_2/M_1 & 0 \\ 0 & 0 & S_2/S_1 \end{bmatrix} This diagonal matrix
D maps cone responses, or colors, in one adaptation state to corresponding colors in another; when the adaptation state is presumed to be determined by the illuminant, this matrix is useful as an illuminant adaptation transform. The elements of the diagonal matrix
D are the ratios of the cone responses (Long, Medium, Short) for the illuminant's
white point. The more complete von Kries transform, for colors represented in
XYZ or
RGB color space, includes matrix transformations into and out of
LMS space, with the diagonal transform
D in the middle. ==CIE color appearance models ==