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The Picture Splice as a Problem of Video Recording*
BY F. N. GILLETTE
GENERAL PRECISION LABORATORY, PLEASANTVILLE, NEW YORK
Summary — Producing an invisible picture splice is one of the major problems of present-day video recording. The various quantities which must be controlled to produce an invisible splice are enumerated with special emphasis on the persistence characteristic of the cathode-ray-tube phosphor.
INTRODUCTION
THE TERM "video recording" might be defined as the process of making a photographic record of the picture portion of television-program material from the face of a cathode-ray tube. It involves a combination of the photographic and television arts. This union gives birth to a number of problems of technique which were not encountered in the practice of either of the parent arts.
This paper will consider just one of these problems, that of making the picture splice invisible. Most of the many factors involved here will be covered as briefly as possible in order that more time can be given to a consideration of the cathode-ray-tube phosphor and its influence on the splice.
To avoid certain ambiguities that would otherwise come up it is assumed at the outset that the film produced by video recording is to be used for theater projection and that it is produced by the directpositive method. That is, that a positive film is obtained in a single photographic step by exposing the film to a negative video picture on the cathode-ray tube.
Since the motion picture and television industries are both very large and are firmly standardized on their present frame rates of 24 and 30 frames per second, video recording equipment is obliged to take 24-frame pictures of 30-frame events. The way in which this is accomplished is illustrated in Fig. 1. The upper figure represents the vertical scan of the television system. The scanning beam starts at the top of the picture, progresses at a constant rate to the bottom and returns rapidly to the top to start the next scan. A single sweep
* Presented April 5, 1949, at the SMPE Convention in New York. 242 SEPTEMBER, 1949 JOURNAL OF THE SMPE VOLUME 53