<title>Dual Mode Calligraphic/Raster Color Cathode Ray Tube (CRT) Projector</title>

Abstract

Dual mode calligraphic/raster color cathode ray tube (CRT) projectorRichard E. HolmesSystems Research Laboratories, Inc. 2800 Indian Ripple Road, Dayton, Ohio 45440AbstractWider and brighter are key words when describing the wants of users of projection television (TV). Higher resolution and truer colors also rank high on the list of desirable features. In aircraft flight simulators, there is the need for static, and sometimes dynamic, raster shaping for off-axis projection on large dome screens. To top off these conflicting requirements is the need for time shared calligraphic (stroke writing or vector refresh) and raster TV operation in some computer image generation systems.This paper describes some of the concepts being investigated for such a cathode ray tube (CRT) projector. Problems associated with optics, color convergence, cooling of the CRT faceplates and deflection are discussed. In addition, the problems associated with the side-by-side merging of multiple projectors for very wide field of view projection (Videorama) are addressed.Background and objectiveIn 1929, Ed Link constructed his first trainer to teach people to fly. Not only did he make it possible for an emerging aircraft industry to grow, he also created a new technology that of simulating given situations to train people to perform effectively in real time. The development of visual displays that have become progressively more is fast becoming a significant facet of simulation. Originally, TV cameras flew over large terrain model boards to generate realistic scenes. Now a new wave of image generation is coming into prominence that of computer image generation (CIG).Three forms of CIG have emerged. One presents the data to the display as a high resolution raster not unlike home television but much sharper in detail. A second controls the colored light beam on a CRT display in a calligraphic (also known as stroke writing or vector refresh) mode much like a painter moves a brush over a canvas and lays down a picture composed of strokes of color. The TV type raster is better for large area, particularly daylight, scenes while the calligraphic is better for point source lights such as runway lights in a nighttime scene. With this background, it becomes obvious that a system that combines the use of a TV sawtooth or triangular wave sweep for wide area scenes time shared with the capability to display point source lights is an attractive choice for a simulator CIG display.Mays reported on such dual mode displays in 1981 and 1982, using 25-inch shadow mask color TV cathode ray tubes, -^'^ while the author has reported on TV projector technology, trinoscope technology, and visual systems used in simulation and training during the same time period.^'*'* This paper will discuss how these technologies are being combined to produce a high resolution, high brightness dual mode calligraphic/raster color TV projector specifically tailored for engineering and training simulators.System configurationIn the author's paper on trinoscopes^ given at the 1981 SPIE technical symposium, it was shown that a full color CRT image can be projected using many arrangements of three CRTs, lens, and image combining schemes. From an optical standpoint, the simplest and most efficient format for a color projector uses three CRTs and three lenses with the full color image achieved by combining the red, green, and blue components of the image on a common screen. All other techniques have losses due either to the image combining optics or due to the relatively large distance from the CRT to the first element of the lens or they are influenced by the earth's magnetic field by different amounts while being moved (such as will occur on a simulator motion base). It is this simple optical merging approach that SRL has initially selected to implement in the dual mode calligraphic/raster color CRT projector.150