AdadlaA.109 net.games utzoo!decvax!ucbvax!ARPAVAX:CAD:teklabs!tekmdp!dadlaB!dadlaA!steve Thu Apr 29 09:06:55 1982 Rastor VS Directed Beam There are two unrelated things being discussed here: First off there are two methods of putting phosphor on a screen to allow color (Shadowmask and Beam Penetration) and there are two ways to build the driving circuitry for the CRT (Vector (or "directed beam") and Rastor). All four combinations of these are possible. The way that Beam penetration works is as follows: Two phosphors are mixed together that have different response curves to the electrical potential of the beam striking them. One of them has a fairly linear curve, while the other has one that appears quadratic. Thus at low potentials the linear phosphor is much brighter than the quadratic phosphor, so its color comes through. At high potentials the quadratic phosphor is brighter, so its color comes out. At potentials in between a varied mix of the two colors comes out. There are two problems with this technology: First off one has to switch KV's at computer speeds to control the potential of the beam as it hits the screen (non-trivial), and second - there is no way I have heard of to use all three primary colors with this technology. All of the displays of this type I have seen use Green (linear) and Red (quadratic) thus providing yellow and orange as well. Such phosphor could be driven with rastor-scan driver circuitry (though it would be pretty useless), and directed-beam can be used with a shadow-mask tube - which appears to be what Attari is doing with Tempest. Thought directed-beam is used, there will still appear to be some discontinuity in vectors due to the granularity of the phosphor on the beam surface. Naturally, a standard television uses a shadow-mask tube and rastor scan driver circuitry. I hope this clears up some of the conflict. Steve Den Beste Tektronix (One of the worlds largest makers of high quality graphics terminals) ----------------------------------------------------------------- gopher://quux.org/ conversion by John Goerzen of http://communication.ucsd.edu/A-News/ This Usenet Oldnews Archive article may be copied and distributed freely, provided: 1. There is no money collected for the text(s) of the articles. 2. The following notice remains appended to each copy: The Usenet Oldnews Archive: Compilation Copyright (C) 1981, 1996 Bruce Jones, Henry Spencer, David Wiseman.