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Historical and Theoretical Data 13
Later Ives23 discovered that his original contention as to the colorsensation curves would not hold water, as they had been proved not to be color-sensation curves at all, but merely color-mixture curves chosen on a purely arbitrary basis, and he, therefore, modified his statements; but still adhered to the importance of the curves for trichromatic photography.
As a matter of fact the curves, given by Ives, are not correct Maxwell curves, these latter possessing negative values in parts. In Fig. 1 B are given Abney's color-sensation curves, wThich may be considered typical of those of other investigators. The difference between the two sets of curves is very marked.
A. A. K. Tallent24 said: "In your issue of Dec. 31, Mr. H. Farmer asks if Mr. Ives can support his claim to the principle that with any trichromatic process the densities of the negative color records must correspond quantitatively with Professor Maxwell's color mixture curves. I venture to say that this claim is unsupportable, and state my reasons below. Maxwell, by empirical methods, found three hues of the spectrum, which when combined in appropriate proportions would counterfeit (approximately) all spectrum hues, white and the purples, in their attributes, hue, luminosity and purity. Synthetically Ives, in his kromskop, employed substantially Maxwell's reproduction colors and adopted the latter curves in the making of the color record negatives. In counterfeiting the spectrum colors by the kromskop the process is substantially a re-performance of Maxwell's experiments, and his curves foretell what colors result from mixtures of his three reproduction hues. Printing, It has been customary to employ Maxwell's curves for the record making in three-color printing, using pigments of complementary or minus ( — ) hue to those employed by Maxwell. Here, further analogy to the kromskop method ceases, for the colors resulting from pigmentary mixtures are not necessarily those which could be deduced from Maxwell's curves. What colors (in hue, luminosity and purity) actually do result from mixtures of pigments can only be determined by trial under the conditions of actual typographic printing. To secure correct or approximately correct reproduction in colors by three (or more) pigments, Maxwell's curves are not suitable, but in their stead curves derived from actual mixtures of properly chosen pigments, made under the usual working conditions (screen negatives, etc., and typographic printing) should be used. 1 have no hesitation in saying that to use Maxwell's curves for printing is wrong, both in principle and practice, and I think this incorrect principle is a barrier to progress of this, the most important branch of three-color work, and that it should no longer go unquestioned.
Von Hubl's Views. — A. von Hiibl25 came to the conclusion that the Young-Helmholtz, or Clerk Maxwell, theory had nothing to do with, or at least possessed no importance for three-color work. He pointed out that as every color can be split up into simple spectral colors, it will be