Some Lighting Problems in Color Cinematography<!--<xref ref-type="other" rid="fn1-10.5594_J14726">*</xref>-->

Abstract

In additive processes the primaries are generally blue-violet, green, orange spectral bands, which are not narrow and overlap to some extent. The exposure latitude of a color-screen process is less then that of black-and-white negative stock. Underexposures often tend toward excessive blue, and overexposures toward some other predominant color, due in some measure to differences in the foot and shoulder of the characteristic curves of the emulsion when exposed to the three primary bands. — Overexposure results in dilution of the colors, due to invasion of each primary into its neighbor's territory. There is thus a color-saturation latitude in the screen or matrix, distinct from a true emulsion latitude. The object here is to discuss a method of calculating the approximate range of studio light-intensity that will preserve the best color balance of which any particular additive process may be capable. — For Dufaycolor film, a wedge spectrogram of suitable sleepness is made representing average exposure, such as from a density of 0 to 2.5. Upon development and reversal, the peaks throughout the wedge spectrum are shown as completely saturated (i.e., 100 per cent of the reseau or matrix saturation). But as any spectral zone is followed downward from the peak, the color becomes diluted and may become even white as the image approaches the base line, and, therefore, maximum expousre. — This is caused by the fact that, upon overexpousre, scattering carries the light behind (say) a green element into the region of neighboring blue and red elements, so that the resulting color is reseau-green plus some blue and red, or reseau-green plus white. The effect is accentuated in reseau composed of less saturated color elements. By measuring from the peak to the position on any ordinate where distinct dilution becomes apparent, the permissible range of light-intensity on the set can be computed from the difference of the log opacities of the two points on the ordinate.