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Fig. 1. Two-element barrier.
used it in 1941 to show projected stereoscopic motion pictures in Russia.
The use of parallax barriers as external attachments to cathode-ray tubes for stereoscopic television is included in several patents. The use of such parallax barriers inside a cathode-ray tube, as a positive means of insuring that portions of a mosaic screen would be subjected to bombardment only by a predetermined electron beam, was first revealed in German Patent 736,575, issued June 22, 1943. The application date is July 12, 1938, and the inventor was Dr. Warner Fleshig of Fernseh A.G.
Principle and Geometric Relationships
The application of the parallax barrier to stereoscopic pictures can serve to illustrate the principle (see Fig. 1). Two pictures taken from slightly separated points of view and designated as left and right views, are divided into fine strips and reassembled on an alternate basis: RI, L2, R3, L4, R5, etc., (the odd numbered L strips and the even numbered R strips are not used). In front of the reassembled picture (labeled "I" plane) there is placed a series of opaque strip barriers separated
by transparent strips of equal width (labeled "B" plane). If the barrier is properly located between the picture and the viewer's eyes (labeled Ot and Or), the left eye will see only the strips L2, L4, L6, etc., (the R strips being hidden by the barriers). Likewise, the right eye will see only strips R1} R3, R5, etc. If the strips are of such small width that they are not individually resolved by the eye, a stereoscopic picture results, since each eye sees only the picture corresponding to its field of view.
From simple geometrical considerations it is possible to determine that the relationship between image distance (D), distance between image strip centers (I), separation of eyes (O), and distance of eye plane to image plane (C), is:
1C
0 + 1
(1)
Although the distance between the eyes (labeled as "O" points) and the image increases steadily in going from the center to the edges of the image, the bandwidth of the picture strips and barrier strips is constant and is independent of the angle between any image
12
July 1952 Journal of the SMPTE Vol. 59