Live Flying-Spot Color Scanner J. H. HAINES G. R. Τ INGLE Y This new color-television system, the Vitascan, (RCA) simultaneous color-television system.1 The 18- X an all-electronic version of the old-style me­ 24-inch scanned area limited the device to head and shoulder chanical type, is the simplest and most reliable pickups.2 Although 937A multiplier phototubes were used, live-action color system now in existence. It the light collection was severely restricted by the 5/16- X can be regarded as using the reverse of con­ 15/16-inch pickup area. ventional studio methods, as the flying-spot The Du Mont color-scanner development program, tube is substituted for the image-orthicon which began in 1949, took advantage of the newly avail­ camera tube and clusters of phototubes replace able 2-inch multiplier phototubes. Although the trans­ regular studio lighting equipment. mission of slides, film, and opaques was achieved with considerable success, it was not until 1954 that components and techniques had sufficiently improved to allow the OLOR-TELEVISION PICTURES of high quality contemplation of a satisfactory color scanner for limited Cwithout the use of expensive and complicated color- live pickup work, which would surmount some of the television cameras or highly trained and skilled shortcomings of earlier equipments. The real technical camera and maintenance crews are now produced by the breakthrough came with the commercial availability of the "Vitascan" system, as developed by the Allen B. Du Mont first 5-inch multiplier phototubes, the Du Mont type 6364. Laboratories, Passaic, N. J. It is, in fact, a modern all- At first, efforts were directed toward providing a live- electronic version of the earliest forms of mechanical live action color pickup of a Ί1/2- X 10-foot scanned area solely television pickup which employed the flying-spot scanning as a signal source for research purposes. However, not­ principles. withstanding its inherent limitations, it became apparent Although Vitascan cannot displace storage-type color- that a very definite use could be made of the principle in television cameras, it is expected that its unique advantages normal color-broadcasting operations. A commercial ver­ will earn it a modest place in color-television programming. sion of this device, the Vitascan, was designed and a proto­ This article proposes to explain its virues and shortcomings. type was demonstrated publicly for the first time at the On an historical level, it is interesting to note how the National Association of Radio and Television Broadcasters present technical state of the art has allowed this revitaliza- (NARTB) Convention in May 1955. This article is not tion of the old flying-spot principle. Thus, basic principles intended as a detailed description of the present com­ are discussed, and evolution of a workable system leading mercially available equipment, but rather as a history of its to present commercially available equipment is traced. parentage. HISTORICAL REVIEW BASIC PRINCIPLE OF OPERATION THE ANALYSIS AND SYNTHESIS of a subject by television THE LIGHT from a high-voltage high-beam current flying- was first achieved by J. L. Baird, in England, in 1923. He spot scanning tube, which emanates from the unmodulated employed a 30-line mechanical scanning system. As late rectangular scanning pattern, is focused onto the subject or as 1937, the British Broadcasting Company (BBC) in scene being televised through a suitable lens system. London, England, programmed with a Baird mechanical As this light spot traverses the scene in its regular pattern, live-pickup flying-spot scanner operating at 240 lines. it is reflected from the various objects; the amount and In advancing from 30 to 240 lines, the mechanical scanner color of reflected light at any given moment varies with the system was doomed for two major reasons. First, the reflection factor and color characteristics of that part of the extremely acute mechanical problems and, second, the scene. The scanning light incident on the scene is therefore lack of sensitivity of the then available photocells. Since modified or modulated by the different reflective charac­ multiplier photocells were not available, the low signal teristics of the scene from one part to another. These level gave excessive noise when amplified, thus limiting variations in intensity and color of the reflected light are the action to head and shoulder close-ups. picked up by groups of multiplier photocells, suitably dis­ The first nonmechanical live pickup, using a cathode-ray posed around the scene, which linearly convert the light tube, was demonstrated early in 1947 during the first energy to varying currents for processing through the normal Federal Communications Commission's (FCC) color hear­ color-video apparatus for flying-spot scanners. ings in connection with the Radio Coporation of America The phototubes are covered with suitable color filters which, in combination with the spectral emission charac­ Revised text of conference paper presented at the AIEE Winter General Meeting, teristic of the scanning tube and the response of the photo­ New York, Ν. Υ., January 30-February 3, 1956, and recommended for publication by the AIEE Committee on Television and Aural Broadcasting Systems. tubes, determine the spectral characteristics of the system. J. H. Haines and G. R. Tingley are with Alien B. Du Mont Laboratories, Passaic, Ν. J. The major differences between the flying-spot scanning 528 Haines, Tingley—Color Scanner ELECTRICAL ENGINEERING operation for the transmission of live pickup and that for transparencies are : (1 ) the scanned area is many thousand times larger for live pickup than for slide or film operation ; (2) the scanning light is reflected from solid objects rather than transmitted through flat material as in the case of a transparency; (3) using a multiplicity of phototubes, lighting effects similar to other live-action television systems are provided ; (4) controlled illumination, in addition to the light from the flying-spot, must be provided in the studio; and (5) special television previewing techniques must be employed. In visualizing how the Vitascan live-action scanner operates, it is helpful to regard the system as being the reverse of conventional studio television operation. Clusters of phototubes replace the studio lighting fixtures and the flying-spot tube is substituted for the image-orthicon camera tube. Normally, light from the studio fixtures illuminates the scene, and reflected light is gathered by an objective lens onto a light-sensitive electrode, where it is transformed by the scanning process within the camera tube into electric Fig. 1. Television studio, showing Vitascan and phototube clusters. currents. In contrast, the scanning tube and its lens, placed where the camera would normally be, produce the light and perform the scanning operation at the same time. Some of this light reflected from the scene is intercepted by the studio, providing adequate illumination for studio the phototube clusters and converted into electric currents. action without upsetting the scanning operation. During The analogous relationship described in the foregoing this same period that the lights are pulsed on, the photo­ was recognized by the early pioneers in television; this tubes or associated video amplifiers, or both, are keyed off relationship was described by Lance and Percy in 19353: to prevent overloading. In addition to being lighttight, "In this studio there has been a great deal of work done to noise is further reduced by employing reflective materials produce an artistic effect by correct lighting of the artists; on the unscanned walls and ceiling, thus increasing the light in fact, it was found that, since each photocell could be directed to the phototubes and additionally softening the controlled separately to give the correct balance between shadows. top, side, and back lighting, in imitation of the lighting of a floodlight studio, the simplest way of working out the EQUIPMENT COMPLEMENT lighting effects was to regard the scanning projector as a IN ITS PRESENT FORM, the Vitascan is operated as a one camera, and the photocells as light sources, placing them or two "camera" system. The "cameras" which, in and altering their gain from that point of view." actuality, are flying-spot scanners, may be fixed or mobile. One favorable arrangement, which was used at the initial STUDIO REQUIREMENTS public demonstration at the 1955 NARTB Convention, INASMUCH AS THE VITASCAN SYSTEM operates by virtue of a includes the Du Mont multiscanner equipment to provide a scanning light beam, no illumination other than that from fixed scanner, augmented by a mobile scanner packaged to the controlled scanning source can be allowed to reach the resemble a standard image-orthicon camera. phototubes during the scanning period because this extrane­ Fig. 1 shows the studio of 200 square feet at the NARTB ous light will only produce noise. Convention. The equipment complement included the The studio, therefore, must be sealed against ambient following items: (1) two scanning light sources, one mobile light. Eliminating all ambient light, however, would leave and one fixed unit, utilizing the Du Mont multiscanner; the studio in relative darkness because the light from the (2) seven clusters of Du Mont 5-inch multiplier phototubes; scanner is insufficient to illuminate the studio adequately. (3) six pulsed light fixtures; and (4) processing amplifiers. This acute problem was literally a stumbling block in The Du Mont multiscanner, as seen in Fig. 2, is a flying- earlier versions of live scanner operation, since lack of light spot scanner system for slide, opaque, and motion-picture seriously restricted the movement of performers about the film pickup. It utilizes a 7-inch high-voltage cathode-ray studio, made it impossible to read, and produced a staring tube operating at 40 kv. The tube, which is aluminized, expression on the faces of the actors. • employes a short persistence zinc-oxide phosphor, coated onto The difficulty of providing adequate light in the studio a high-quality nonbrowning neutral-density face plate.