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Lighting Distortion in Television*
BY RICHARD BLOUNT
GENERAL ELECTRIC COMPANY, NELA PARK, CLEVELAND 12, OHIO
Summary — Improved television pictures can be produced by (1) limiting the contrast of the original scene, (2) by selecting light sources that when combined with the camera-tube spectral sensitivity provide accurate tonal rendering, and (3) by using lighting techniques that aid in creating an illusion of three dimensions on the receiver screen.
IMPROPER LIGHTING TECHNIQUE in television may result in three forms of picture distortion : (1) Loss of detail caused by brightness contrasts that exceed the latitude of the electronic equipment. (2) Absence of depth due to improper distribution of light over the scene. (3) Rendering of colors in unnatural relative gray values caused by spectral characteristics of the light and of the camera tube.
The first type of distortion occurs when illumination levels in the scene are too uneven. Excessive illumination on some surfaces of the scene and inadequate light on others result in a picture lacking in detail because the range of brightness in the scene exceeds the latitude of the electronic equipment. This occurs, for example, when most of the light comes from overhead; upper portions of people's faces are overexposed while shaded areas, such as eyes, are underexposed.
The situation can usually be remedied by providing a general level of vertical surface illumination that is at least equal to, and preferably somewhat greater in intensity than, the horizontal surface illumination. In both cases the illumination may be supplied from broad sources, some mounted overhead and others aimed almost horizontally into the set from just high enough off the floor to allow free passage of the operating personnel and their equipment.
Some loss of detail may also be encountered even when incidentlighting levels are entirely adequate and sufficiently uniform. Difficulty arises where the reflection factors of the various scene components differ widely. Two separate materials, one dull black and
* Presented April 4, 1949, at the SMPE Convention in New York.
DECEMBER, 1949 JOURNAL OF THE SMPE VOLUME 53 625