CONGRESSES AND CONFERENCES

CONFERENCE ON COLOR PHOTOGRAPHY AND CINEMATOGRAPHY

In the period from October 23 to 27, 1950, a conference on color photography and cinematography was held in Moscow. This conference was the second convened by the Commission on Scientific Photography and Cinematography under the Division of Chemical Sciences of the Academy of Sciences of the USSR.

The conference, which attracted a large number of participants from a wide variety of research, educational, and industrial organizations, was marked by a considerable rise and demonstrated the significant scope of scientific and engineering activity in our country in the field of color photography and cinematography, as well as major successes in this direction. Almost all the reports—and there were 14 of them—were very substantial and became the subject of lively and detailed discussion.

With the exception of two communications, all the remaining reports were devoted chiefly to the currently principal direction in the development of photographic technology for color reproduction—color photography and cinematography on multilayer materials with color development. These reports were grouped around four problems: 1) physicochemical questions of color development, 2) organochemical questions of the manufacture of multilayer materials, 3) the technique of color cinematography, and, finally, 4) sensitometry of multilayer materials and colorimetry.

Four reports were presented on the problem of color development.

In the report by Prof. K. S. Lyalikov on work carried out by him jointly with B. A. Tsarev and Ya. L. Leibov, information was given about interesting experiments on determining the character of the difficult-to-capture intermediate products in the reaction of color development. In this reaction the oxidation products of the developing substance, which reduces the silver halide of the color-photographic material to metallic silver, enter into interaction with color-forming components present in each of the elementary layers of the multilayer material, and form dyes with them. Naturally, the chemistry of this process is of interest. K. S. Lyalikov, studying spectrophotometrically the coloration of a jet of color developer passing through a layer of silver halide, detected the scarlet coloration of the semiquinone ion

Since this ion is very unstable, already at a distance of 2–3 cm from the silver-halide layer the coloration disappeared, changing into dirty-violet—

... coloration of the products of semiquinone condensation. If a dye-forming component is introduced into that part of the jet where there is a scarlet coloration of the semiquinone, then a coloration of the forming dye appears; if, however, the component is introduced into the lower, violet part of the jet, no change in coloration is observed. Thus, the fact was established that semiquinone is formed as the primary product of the reaction, and it was shown that the coupling of the oxidation product serving as the aim of the process with the dye-forming component can occur in two stages.

In the same report, K. S. Lyalyakov described the results of a study of the kinetics of changes in the concentrations of the substances composing the color developer in the course of oxidation of the latter by atmospheric oxygen or by silver halide, the character of the influence of potassium bromide and acid developer (pH) on the course of color development, and, finally, measurements of the normal potentials of developing substances used for color development (derivatives of paraphenylenediamine), knowledge of which is necessary for understanding the mechanism of color development.

V. S. Chelyubov, in a report presented by him jointly with A. N. Iordanskii and S. A. Bongard, set forth the results of a very interesting investigation of dye yield in color development. By dye yield is understood the ratio of the amount of dye formed in this process to the amount of metallic silver, which is, in a certain sense, a by-product of the reaction accompanying the subsequent removal. It was shown experimentally that in the color-development reaction leading to the formation of a magenta dye, the molecular yield—the number of dye molecules per atom of reduced silver—is exactly 0.25, while in the reaction leading to the formation of a particular blue dye it is 0.5. At the same time it proved that the ratio of the optical density of the blackening accompanying the formation of a particular dye to the monochromatic optical density of the corresponding color field (without silver) at the absorption maximum, called by the authors the relative photographic yield, is a variable quantity for different photographic emulsions (the experiments were performed on single-layer film samples) and under different development conditions. Analysis of the question showed that the discrepancy between the results of the two parts of the investigation is only apparent. The nonconstancy of the relative yield is explained by the fact that, whereas the surface concentrations of the dye and metallic silver are strictly proportional to each other, the surface concentration of silver in the blackening and the optical density of the latter are not proportional because the dispersity of the silver is not constant at different development times, under different exposures acting on the layer, when different types of emulsions are used, etc. As a consequence of this circumstance, the characteristic curves and the sensitometric parameters derived from them, obtained by evaluating in one case the silver (in the absence of dye) and in another case the dye (in the absence of silver) images, differ markedly from one another.

Prof. G. P. Faerman, in a joint report with N. N. Shishkina on the role of alkali in color development, convincingly showed that the basic regularities of color and black-and-white development fit into the unified scheme developed by him earlier in his electrochemical theory of development. Indeed, in color development the surface concentrations of the dyes formed in each of the elementary layers of a multilayer film, at an unchanged development time, ...

turn out to be strictly proportional to the pH of the developing solution (in the investigated interval from \(pH = 8.3\) to \(pH = 11.6\)). This indicates that the rate of color development as a whole is determined chiefly by the rate of formation of the primary oxidation products of the developing agent.

Similar conclusions were reached in the study reported at the same session by V. A. Veidenbakh and E. A. Karpovich. At optimum development times the authors established the existence of a linear relation between the surface concentrations of dyes in a multilayer film and the logarithm of the concentration of the developing agent in the solution. This is as it should be according to the electrochemical theory of development, since the potential difference between the silver system and the developing system is linearly related to the logarithm of the concentration of the developing agent.

On questions of organic chemistry connected with the manufacture of multilayer color-photographic materials, two papers were read.

I. A. Solov’eva delivered a paper, presented by her jointly with the recently deceased major figure in Soviet color cinematography, Candidate of Chemical Sciences G. I. Arbuzov. The paper was devoted to a detailed survey of film-forming dye components introduced into each of the elementary layers of multilayer films and papers. None of the components used in practice satisfies all the requirements that in principle are imposed upon them: good solubility, high reactivity, complete nondiffusibility in the layer, absence of desensitizing action, proper character of the spectral properties of the dye formed, etc. In their spectral properties the purple dyes formed in the middle layer of a three-layer film are not very satisfactory. Most components give dyes that are insufficiently stable over time and under the action of light; blue dyes in particular are not very stable.

The second paper was delivered by I. I. Levkoev jointly with Z. P. Sytnik and S. V. Natanson and was devoted to sensitizing dyes for color-photographic materials. It should be borne in mind that of the three emulsion layers of such materials, two—the middle and the lower—are sensitized to the green-yellow and, respectively, to the orange-red regions of the spectrum. The requirements of color separation compel the use of sensitizers that render the emulsion sensitive to comparatively narrow regions of the spectrum, if possible with a single maximum. However, highly active sensitizers (and it is precisely such sensitizers that have to be used here), as a rule, are prone to aggregation both in solutions and especially in adsorption layers. Different forms of polymerization and aggregation of dyes correspond to different absorption bands; as a result, such dyes, often being present simultaneously in several forms, usually sensitize the silver halide of the photographic emulsion over a very broad spectral interval. Another difficulty is that the presence in emulsions of the components necessary for color development causes a strong lowering of the sensitizing action (desensitization). As a result, the choice of sensitizers for the purposes of color photography on multilayer materials is limited to a small number of “component-resistant” dyes that provide comparatively narrow sensitization zones.

I. I. Levkoev examined in detail the question of the connection between the chemical structure of sensitizers (the type of heterocyclic nuclei entering into the dye molecule, the nature of the substituents, etc.) and their

optical properties and photographic action under conditions of the presence of a dye-forming component. The second half of the report was devoted to comparing the phenomenon of desorption of a sensitizer from the surface of silver-halide crystals by a component present in the emulsion, and the inhibitory action of the latter on the effect of optical sensitization. These phenomena, apparently, are closely connected with one another. It is curious that, for one of the combinations studied of a dye with a component in aqueous solutions, a certain physico-chemical form is produced which, possessing high light absorption, is completely not adsorbed on silver halide and does not sensitize it.

Three reports were made on the technique of color cinematography.

V. I. Uspenskii, with S. M. Antonov, devoted his report to the urgent problem of countertyping color motion-picture negatives. The point is that the production of a large number of positive copies of films released on the screens of our country cannot be carried out by printing from the original and sole negative, which would be subjected to the risk of damage and even destruction. In black-and-white cinematography, intermediate negatives are always made for this purpose; the corresponding process is called countertyping. In color cinematography this problem has not yet been solved, since a multistage color reproduction always leads to a sharp deterioration in the quality of the color image. V. I. Uspenskii illuminated the paths along which the solution of this important technical problem is proceeding. To this it must be added that the problem of long-term storage of color films is intertwined with this problem, since, as is known, the dyes of a multilayer process have a tendency toward gradual discoloration. This problem is solved by obtaining three black-and-white (silver) intermediate color-separated positives, which keep very well.

The report of I. A. Nechaeva on the Soviet hydrotype method of obtaining color films stood somewhat apart. This method, begun by development in several variants as early as the beginning of the nineteen-thirties, consists in principle of printing, by a technique similar to that of polygraphic printing, three single-color images from readily diffusing dyes in gelatin layers (in so-called matrices) onto pure gelatin film. As a result of diffusion of the dye from such a layer onto this pure film, three images are successively obtained. One of the most difficult circumstances is their exact superposition. The mastering of this method was interrupted by the war; at the present time, however, great successes have been achieved which make it possible to carry out hydrotype printing starting from a negative obtained on a multilayer film (the drawback of the hydrotype in the past was the necessity of obtaining three color-separated motion-picture negatives free from temporal and spatial parallaxes, for which it was necessary to carry out filming with very complicated motion-picture cameras with optical splitting).

Finally, the report of S. M. Antonov was devoted to the small but extremely urgent question of the objective setting of light (i.e., the regulation of its spectral composition) when printing color images on multilayer materials. The point is that the always-present mismatch of the sensitivities and contrasts of the three elementary layers of both the negative and the positive materials makes it necessary in practice always to vary the spectral composition of the radiation of the printing device until a visually satisfactory positive color image is achieved. Until now this has been done purely empirically, by means of numerous trials. S. M. Antonov

... and N. S. Ovechkin (in another paper) illuminated ways of finding a rational solution to this problem.

The final group of papers was devoted to the photographic sensitometry of multilayer color-photographic materials and to questions of color science connected with it.

Prof. N. D. Nyuberg, jointly with G. S. Baranov and N. S. Ovechkin, in his paper presented his very interesting and broad views on the system of sensitometric testing of color-photographic materials. These tests, in the speaker’s opinion, should consist of two groups:

1) gradation tests, consisting in establishing the dependence of the photographic effect on the amount of illumination of radiation of a given spectral composition, i.e. in obtaining characteristic curves, and

2) color-separation tests, consisting in establishing the amounts of illumination, equivalent in photographic action, for standard white radiation and for the investigated radiations of one or another spectral composition.

In the second paper, devoted to the relation between the sensitometric properties of color-photographic materials and distortions of color reproduction, N. D. Nyuberg emphasized that distortions of color reproduction are likewise divided into gradation and color-separation distortions. Correction of the former does not eliminate the latter. To evaluate color reproduction it is advisable to use not the usual additive coordinates, but the subtractive color coordinates, far more convenient in color photography, which are the surface concentrations of the dyes of the positive material, expressed in certain units tied to the properties of the eye. Color-separation distortions are caused predominantly by the presence, in each of the dyes, of broad absorption bands extending into the spectral zones of light sensitivity of those elementary layers that are intended for “separating out” other dyes.

Thus, in each image in an elementary layer there are two harmful and one useful contrast, the ratio of which characterizes the quality of color separation for each given elementary layer. In the absence of gradation distortions, color-separation distortions always appear as an approximation of the photographed colors to achromatic ones (a decrease in saturation). As for gradation distortions, here what is essential is not only the correspondence of the contrasts of the elementary layers to one another, but also the obligatory use, in constructing the image, of only rectilinear portions of all three characteristic curves. Otherwise, shadows in the colored elements of the image are reproduced with distortion. Consequently, the requirements imposed on the form, mutual position, and length of the usable portion of the characteristic curves of the three elementary layers are exceptionally high.

Yu. N. Gorokhovskii, jointly with D. K. Balabukha and T. M. Levenberg, delivered a communication on a cycle of investigations of the sensitometric properties of color-photographic materials. Determining the limits within which black-and-white and color materials possess identical properties and, correspondingly, the limits within which color-photographic materials possess specific properties is a necessary condition for constructing a unified system of sensitometry for all types (black-and-white and color) of photographic materials. A spectrophotometric method was set forth for measuring the surface concentrations of dyes when they are present together in the film. On the basis of the use of this method and of other newest sensitometric techniques

the spectral properties of color-photographic materials, deviations from reciprocity for them, and the distinctive phenomenon of mutual influence of elementary layers during color development were studied in detail. This latter consists in the fact that the form of the characteristic curve of each of the layers proves to be dependent on the exposure level of the other layers, since depletion of the developer inside the multilayer film occurs to a greater extent the more strongly a given area of the film has been exposed. All these data made it possible to formulate the basic requirements for the methodology of sensitometric tests of multilayer materials.

In addition, the paper described the distinctive features of the resolving power of multilayer materials, which in the material as a whole is much lower than in the component elementary layers. This is due to the fact that each of the layers scatters light, forming an optical image on the material, although this light does not take part in forming the photographic image on the given layer.

The last paper in this section was delivered by N. S. Ovechkin, who set forth the content of the three-zone system of color coordinates developed by him, which represents a convenient simplified method for evaluating color in subtractive synthesis. The system provides for the schematization of real curves of light absorption by means of three-step curves. The primary colors are three radiations transmitted by light filters with “rectangular” spectral transmission curves. Using this system, one can evaluate the result of subtractive synthesis with the same speed and ease as with the systems developed for additive synthesis. N. S. Ovechkin has succeeded in successfully applying the scheme he developed to the problem of objective setting of light in color printing, which has already been discussed above.

Historical communications occupied a special place at the conference. In his introductory address at the opening of the conference, the chairman of the Commission on Scientific Photography and Cinematography, Corresponding Member of the Academy of Sciences of the USSR K. V. Chibisov, gave a brief outline of the history and paths of development of color photography and cinematography, drawing the attention of those present especially to the merits of Russian scientists and inventors. Prof. K. S. Lyalikov delivered a special paper on S. O. Maksimovich (1876–1941), a pioneer of domestic color cinematography and a profound and versatile scholar in various questions of the theory of photography and a brilliant inventor. The paper reported many new facts hitherto unknown.

During the conference, an exhibition of scientific-technical and artistic works on color photography was set up in the NIКFI screening hall; participants included the Laboratory of Scientific-Applied Photography and Cinematography of the Academy of Sciences of the USSR, the photographic laboratory of the Academy of Arts of the USSR (S. G. Gasilov), the Lenfoto-Khudozhnik studio (L. L. Zivert), and the Laboratory for Processing Color Motion-Picture Films of the Ministry of Cinematography of the USSR. There as well, the Technical Administration of the Ministry of Cinematography organized a demonstration of a number of color films.

On the whole, the conference, held at a high scientific level and with great audience activity, was a true celebration of Soviet science. It is to be hoped that this first scientific gathering, specially devoted to the complex but fascinating problem of color photography and cinematography that has now entered upon a period of its broad dissemination, will soon be followed by subsequent, still more interesting conferences.

Yu. N. Gorokhovsky