The Optical Magic Lantern Journal (March 1901)

34 The Optical Magic Lantern Journal and Photographic Enlarger. made in pigments which suppress the respective primaries. After nearly 20 years (from the dates of Du Hauron and Cros's publications), although all the materials requisite to experimental success had long been at hand, the principle had not been confirmed by a single really successful result, and was apparently universally discredited. Meanwhile Dr. H. W. Vogel, in 1835, stated as a ‘‘new principle,’ that the negatives should be made by the same spectrum rays that are absorbed by the printing colours, and in the same proportions—in other words, that the “ optical sensitisers,” or colours spectro: copically identical with them, should be tbe printing colours. Tbis was only another way of stating Cros’s principle of printing in colours ‘‘antichromatic ” or complementary to those which produced the negatives. Dr. Vogel's statement of this ‘ principle” disclosed no recognition of the relation which the negatives or printing colours must bear to the physiological analysis of the spectrum colours, thus missing the most vital point ; and it is under no circumstances a true principle in trichromatic photography, but at best involves precisely the same error as the theory that positive synthesis should be effected by screens which transmit all the various rays which have acted to produce the respective photographic ‘‘colour curve” records. I hope I have made it clear that the true function of the printing colours is to subtract most efficiently (specifically) from ordinary white light the visual impression belonging to the respective colour elements, and that this is not effectcd ty colours complementary to the correct photographic action. Notwithstanding the errors involved in Dr. Vogel’s theory as applied to the trichromatic process (he also proposed a more complex analysis), the weight of his authority caused it to be generally accepted in Europe, and it is still a stumbling-block for many experimenters. It was the acceptance of this theory that made Von Hitbl, in 1888, declare that the Young-Helmholtz colour theory is not a suitable basis for a theory of three-colour printing, and that he could not see ia what way it had indicated to me the correct printing colours.* Having no theory to guide him but Vogel's, Von Hibl worked out the details of a mcthod which, assuming that he actually worked to bis diagrams (see the Amateur Photographer, January 19th, 1884, p. 47), would reproduce the spectrum itself as three broad bands of equal and much diluted colour, with only very narrow spaces of blending between. Thus does false theory lead to error; and yet this method, which would completely break down upon the spectrum itself, is described in one of the technical journals, nearly six years after the publication of the principle of colour curve analysis, as ‘' enriching our literature on this subject with the clearest exposition of the theory yet propounded! "' ; Dr. F. Stolze, of Berlin, published a series of articles treating of the theory of trichromatic photography, the dates of which I cannot give, having never seen them in the original. Translations appeared in Anthony’s Photographic Bulletin in September, October, and November, 1888 ; but it has been stated that the original publications appeared some years before. Dr. Stolze was probably the first to mention the Young-Helmholtz theory of colour vision in connection with this subject, and to point out that the most that could be expected of a trichromatic process was that it should more or less perfectly counterfeit most of the spectrum hues to the eye by colour mixtures physically different from the original colours. * Procees Photogram, April, 1888, p. 53, Dr. S:o!ze’s writings were not reproduced in Engl’sh, and did not come under my observation until long after I had published similar observations, which he then claimed, very justly I have no doubt, to have in some measure anticipated. He treated of the subject only as applying to the production of colour prints, and did not formulate a definite principle, or recognise the practical bearing of the Maxwell measurements of spectrum colour mixtures, and his conclusions were distinctly antagonistic to hopes of practical success. My own experiments commenced early in the year 1878, and before the end of that year I had at hand all the material means requisite to success, such as perfect coloursensitive plates, control of the absorption of colour screens, a method of producing half-tone process blocks for carrying out the idea in typographic printing, etc. Nevertheless, my results, even in lantern projections, were crude and discouraging. My theoretical knowledge of the subject was inadequate to discover tha sources of error. Like Du Hauron, |! gradually improved my results by sheer experience, but I am now perfectly convioced that complete succes3 could never have been achieved by such a process of trial and error. I became convinced that a quantitative analysis of the various spectrum hues in terms of three spectrum colours must form the basis of a successful method, and stated this principle and the method of its application somewhat clumsily in a paper read before the Franklin Institute in February, 1S88.* My analysis was, however, imperfect, and it was only after some reference to Maxwell's work in spectrum colour analysis which appeared in Rood’s ‘‘ Modern Chromatics" came under my observation, that I was able to perfect my method, and to clearly and perfectly enunciate the principle of colour-curve analysis and pure-colour synthesis, which I did ia a paper read before the Franklin Institute in November of the sams year.t The application of this principle resulted in the accurate reproduction to the eye of the colours of the objects photographed—something which I then believed, and still believe, had never before been accomplished, and which probably never would have been accomplished by a trichromatic process without recognition of this principle. I think Iam correct in saying that the soundness of my theoretical expasition of the subject was soon recognised by Dr. Stolze, Victor Schumann, and Sir W. Abney, but that it was actively discredited, though without argument, by almost everybody who had previously become identified with the subject in the public mind. Apparently unanimous condemnution by “ practical experts”’ had the effect of persuading most people that my method must be wrong and my results tricked, and the wheels of progress continued to be clogged by voluminous writings which served chiefly as a negative means of discrediting an important truth. I mention these facts in explanation of the aggressiveness which I have shown in my fight for recogaition of this principle, and which has often been mistaken for a mere ebullition of egotism. I submit that, as a conscientious teacher, I could not do otherwise than maintain that by the application of this principle the problem of recording and reproducing colours by photographic analysis and optical synthesis was finally solved. This course on my part has been al] the more necessary because in some pretentious treatises, such as that of Alcide Ducos Du Hauron, published in Paris as recently as in 1897, the principle of colour-curve analysis, to be * Journal of the Franklin Institut , Philadelphia, May, 1888. J y + Journal of the Franklin Institute, Philadelphia, January, 1888, p. 58.