Apparatus for measuring density stimulus values of three primary colors

Claim 1

In a recording spectrophotometer of the flickering beam type for measuring the reflectance R lambda of a colored sample in which a Rochon prism is rotated through an angle Alpha to control the relative intensities of the beams and thereby to compensate for the reflectance of the colored sample and which includes an integrator for automatically calculating tristimulus values X, Y and Z in accordance with the wavelength or frequency of monochromatic light being reflected into the spectrophotometer by the colored sample, the improvement which comprises, a drive linkage between said prism and the integrator, said linkage comprising, a driving element whose rotational angle is directly proportional to K/S where K/S is the Kubelka-Munk function or a recognized equivalent optical density function whose value is proportional to the concentration of the colorant in said colored sample, whereby the values integrated by said integrator are the density tristimulus values KX, KY, and KZ where KX (K/S) lambda x lambda P lambda d lambda KY (K/S) lambda y lambda P lambda d lambda KZ (K/S) lambda z lambda P lambda d lambda wherein x lambda , y lambda , and 2 lambda are spectral tristimulus values of CIE Standard Observer, respectively, and P lambda is a spectral distribution of standard illuminant.