Diagnosis and genetics of defective colour vision / by H. Kalmus.

  • Kalmus, H. (Hans), 1906-1988.
Date:
[1965]
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Diagnosis and genetics of defective colour vision / by H. Kalmus. Source: Wellcome Collection.

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    4 DEFECTIVE COLOUR VISION (adding)* not more than three suitably chosen monochromatic radiations. This fact is the basis of the widely accepted trichromatic theory of colour perception (Yoimg, 1801-2; Helmholtz, 1852) which postulates the existence of three kinds of colour receptors (cones) and which being the most suitable for expounding defective colour vision is adopted here. Quite recently Wald and Brown, as well as Dobelle and Marks (MacNichol, 1964) succeeded in measuring the absorption of single cones in human and primate retinas with a microspectro- photometer. Computation of these measurements showed three classes of cones with absorption peaks of about 430, 540 and 570 m¡x. It should, however, be mentioned that Hering's four-colour theory (1878) which is based on certain antagonisms between complementary pairs (red, blue-green and blue-yellow) can also be applied to some cases of defective colour vision, though the phenomena it describes are probably not happening at the receptor level (pp. 54-55). The trichromatic theory makes it possible to characterize colours (with certain exceptions) by their position in a triangle (Maxwell, 1871), in which the corners represent the colours of suitably chosen red, green and blue monochromatic light (Fig. i). The position of a colour С in such a chromaticity chart is fuUy determined by any two of the three colour coordinates, as the third is automatically fixed. Algebraically we can represent our colour by a match according to the equation С = r.R + g.G + b.B where С is the colour match and r, g, b are the relative amounts or colour coefficients—on an empirical scale—of red (JR.)^ green (G)^ and blue (B) monochromatic radiation. It is interesting that the laws of colour mixing were formulated by the mathematician Grassmann (1809-1877), who was not himself an experimenter, but got interested in the work of Helmholtz. Based largely on Newton's observations he applied his mathematics of dimensions to the laws of colour mixing. He stated that (i) unlike Hghts mixed with like Hghts produce unlike mixtures, (2) like Hghts mixed with hke lights produce like mixtures and (3) every mixture of Hght can be matched by a defmite spectral mixture (Stiles, 1952), Experience has shovm that certain spectral colours, namely the blue and green ones, fall outside the area of colour triangles, which * The addition (mixing) of lights must not be confused with the mixing of pigments, which is a subtractive process, because every pigment removes some radiation from the reflected Hght. Filters also are subtractive.