DIN99 Lab space is based on DIN 6176: 2001-03, and is derived from L*a*b* space, and is designed such that a simple Euclidean difference between two DIN99 values has a better correlation with perceived error than CIE Delta E 76 (L*a*b* dE). It is generall regarded as equivalent to CIE Delta E 94, but with the advantage that it is a euclidean space and the calculation is reversible.
Details of white point
configuration.