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ON THE THEORY OF TONE REPRODUCTION, WITH A GRAPHIC METHOD FOR THE SOLUTION OF PROBLEMS*
Loyd A. Jones, A. S. C. **
THE PROBLEM of ascertaining the exact extent to which it is possible by the photographic process to produce a pictorial representation of an object which will, when viewed, excite in the mind of the observer the same subjective impression as that produced by the image formed on the retina when the object itself is observed has engaged the attention of workers in the field of photography for many years. There are many phases of the subject to be considered, and a complete treatment requires a careful analysis of the various factors upon which depend the operation of our visual perception of space and spatial relations. A complete analysis, therefore, leads not only into the realm of physical science, but also into those of psychology and philosophy. It is not the purpose of this paper to present such a complete treatment, but to deal with a single phase of the subject.
A careful consideration of the various factors upon which depend our visual perception of space leads to the conclusion that brightness and brightness differences (i. e., contrast) are by far the most important factors which are reproducible by the photographic process. The form factor (including size, shape, position, definition, etc.) to which so much importance is usually attached and which is conditioned by the performance of the image forming system, depends for its effectiveness upon the proper rendition of brightness differences. The proper reproduction of brightness and brightness differences, therefore, is of preeminent importance, and it is with this brightness factor and the possibility of its correct reproduction by the photographic process that this paper will deal.
This problem of tone reproduction, as it is commonly called, has frequently been regarded as requiring only the correct reproduction in the picture of the actual physical brightness of the original, and of the actual contrast relations existing between various areas of the object. When we consider, however, that a given brightness or contrast may produce an entirely different subjective impression, depending upon the state of adaptation of the observer's eye, it is obvious that such a treatment of the subject cannot afford a complete solution of the problem. The problem may, in fact, be divided into two general parts: the one, which we may term the objective phase, dealing with the reproduction of the actual physical brightnesses and capable of being completely solved by purely physical
* Published: Abridged Scientific Publications from the Research Laboratory of the Eastman Kodak Company. IV (1919-1920) p. 99. Published in full: J. Franklin Institute. 190 (1920) p. 39: J. Opt. Soc. Amer.. 4 (1920). p. 420. S.M.P.E. Journal. May. 1931. ** Research Laboratories, Eastman Kodak Co., Rochester, N. Y.
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