Agfa motion picture topics (Apr 1937-June 1940)

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visible radiation in equal proportion belongs to the group of neutral or nonselectively colored objects, such as gray, white or black, depending solely upon the extent to which they reflect the incident radiation. All objects which absorb certain wave lengths of the incident radiation to a greater extent than others are selective absorbers. Radiation, which is reflected or transmitted by such objects is different in spectral composition from that which was incident thereon. The color which an object appears to have depends, therefore, on two factors, its absorbing characteristics and the spectral composition of the incident radiation. Most of the natural colored objects are of the reflecting type with selective absorption. Consequently, the vast variety of pigments and dyes and their spectral absorption curves are of vital importance to the photographer. Objects of the transmitting type with selective absorption are best known to the photographer in the form of color filters which are used to selectively absorb or transmit certain portions of the radiation reflected by the object being photographed. The absorption curves of pigments are in general characterized by a more or less gradual cut off in comparison to those of transmitting objects, such as color filters, which must show a relatively sharp cut off. Luminosity Curve and Photicity Curve The ordinates of the visibility curve as previously explained consist of brilliance units. When multiplying these ordinates with those of the spectral reflection curve for any given selective absorber (such as a pigment for instance), and plotting this product against wave length, the luminosity curve is obtained. The area inclosed by this curve indicates the relative brightness of this object for a given light source. Similarly when multiplying the ordinates of the spectral sensitivity curve for a photographic emulsion with the ordinates of the spectral reflection curve of any object and plotting this product against wave length, we obtain a curve which is known as the photicity curve. The area inclosed by this curve is proportional to the photographic brightness of the object considered. These few fundamentals of color should be studied and understood by anyone who concerns himself with the problem of correct photographic reproduction. The solution of this problem, as was previously stated, consists of rendering brightness and brightness differences or contrast in the final print identical to that conceived by the eye from the natural object. In practice it will be found that an additional problem of equal importance exists which requires deliberate distortion or a deviation from correct reproduction in order to secure certain desired effects. Page Fifteei