British Kinematography (1950)

150 BRITISH KINEMATOGRAPHY Vol. 17, No. 5 extent desired. A series of 16mm. motion pictures was made under similar, low-contrast lighting conditions from which a series of prints was made at four different gammas. The lowest gamma was 0.97, and the others were 1.50, 2.04, and 2.50. A number of prints were made from each negative, starting with a light print and gradually increasing the printer light intensity until a very dense print was obtained. These prints were reproduced over a closedcircuit system, and the print density which gave the best picture quality was selected from each gamma. The minimum and the maximum densities were 0.57 and 1.77, 0.48 and 2.04, 0.35 and 2.46, and 0.28 and 2.58, for the gammas of 0.97, 1.50, 2.04, and 2.50, respectively. Another method which appears promising as a means of obtaining better television-picture reproduction, and which is gaining wide commercial acceptance, is the use of low subject-lighting contrast. This method also has the advantage that it involves no departure from standard practice in the processing laboratory. Lighting Requirements. Typical lighting setups showing the placement of the lights in relation to the subject and the camera are shown in Figs. 8 and 9. The balancing light used to control contrast, usually referred to as the " fill-light," should give an illuminance level having a definite ratio to the key-light. The key-light is that light source used to illuminate the highlight area of the subject of greatest interest, and this area is the one on which the exposure is based. The ratio of fill-light to key-light illumination may be measured conveniently by means of photoelectric exposure meters which are equipped to measure incident light. Such meters are used at the position of the subject and are pointed at the light source. When measurements are made in this manner, the ratio of fill-light to key-light illumination is called " lighting contrast." The key-light illuminance should be checked after the fill-lights have been arranged. It should be noted that the term " lighting contrast " is not synonymous with the terms " subject contrast " and " subject brightness range." The true subject contrast or subject brightness range is usually much higher than the lighting contrast, since it takes into account the different luminous reflectances of the various elements of the scene. It can be measured accurately only by means of a flare-free telescopic type luminance photometer, which measures a very small area and which allows the instrument to be situated at a sufficient distance so as not to obstruct any light falling on the subject. Lighting Tests. As a practical approach to the problem, it is possible to make luminous reflectance readings of various areas of the scene with exposure meters which are equipped for making reflectance measurements. The readings obtained with these meters do not, of course, give a measure of the true subject luminance range because of the greater angular response of the meters and because of the possible creation of shadows in making the measurements. These reflected-light readings are, nevertheless, very useful in roughly determining whether or not the various areas of the subject will be rendered correctly by the photographic material. A series of pictures was made on 16mm. film, in which only a single fill-light and a single key-light were used to illuminate the main subject. No top-light was used and the back-lights illuminated the background only. The key-light illumination was constant for all contrasts. Both the negatives and the prints were developed to normal gammas. (Kinescope photographs of these pictures were reproduced as slides in the lecture to illustrate the appearance of the pictures on the image tube.) The lighting contrasts were 1 to 1, 1 to 2, 1 to 3, 1 to 4, 1 to 8, and 1 to 64, respectively. Although the pictorial quality was