Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!watmath!clyde!rutgers!ames!oliveb!sun!cuba!mmp From: mmp@cuba.UUCP Newsgroups: comp.graphics Subject: Re: CRT technology? Message-ID: <11606@sun.uucp> Date: Sat, 17-Jan-87 00:41:31 EST Article-I.D.: sun.11606 Posted: Sat Jan 17 00:41:31 1987 Date-Received: Sat, 17-Jan-87 16:17:43 EST References: <1219@ucbcad.berkeley.edu> Sender: news@sun.uucp Lines: 186 Summary: state of the art in CRTs In article <1219@ucbcad.berkeley.edu>, faustus@ucbcad.berkeley.edu (Wayne A. Christopher) writes: > How close are the color CRT's > used for suns, uVaxes, etc to the current state of the art? (I'd > estimate they're about 80 dots per inch.) How long will it be before > we start seeing 300 dpi color CRT's available? Or are they already > available for very expensive machines? > You just asked the $65,000 question! And you are getting a LONG answer to it. A major difference between monochrome and color CRTs is that the latter has a mask interposed between the CRT's optics and its phosphor. CRT resolution is thus measured as a pitch, which is the center-to- center distance between the little holes in the mask. "Available" CRT pitch specs are: .31mm, .26mm, and .21mm. You may see instead: .30mm, .25mm, and .20mm. It all depends on where you measure it (the mask itself or through the glass in front of it). The .31mm CRT is the one most often found in Suns, uVaxen, etc 19-inch displays. The .26mm CRTs are becoming more popular, as their price has begun to drop now that they are in full production. The price of .31mm CRTs, however, is also dropping as that technology matures, and vendors are not likely to make the switch unless customers demand it (I'd imagine they rather enjoy the extra margins). The .21mm CRTs are now available in sample quantities and production quantities won't be available till later next year (remember, however, that this is vacuum tube technology and production quantities are not made available until there is a LOT of demand for it). I have seen one of these made by Hitachi and I am spoiled for life -- a .31mm and even a .26mm CRT will never look good again! This is definetely state of the art and it'll be a while yet. There's a technology/theory developed by Dr. Carlo Infante, now an independent consultant, that pretty much predicts that moving up in CRT pitch is more important to picture quality than increments in things like amplifier frequency, etc. His work, called Modulation Transfer Function Area (MTFA) actually quantizes the improvement to be expected and it's pretty close my own experience. So, if you believe that, you'd want the CRT (and monitor) vendors to get off their duff and bring us even lower pitch CRTs as soon as possible (which, by the way, also allows to get more picture on the screen!). The problem with fullfiling that wish, such as I have, is that even though all the CRT vendors are "working on it" (i.e. .20mm and .17mm pitch CRTs), it ain't easy to pull and still make them manufacturable. The main problem is easy to understand if you can visualize what happens to a sheet of metal the thickness of a 20lbs sheet of paper when you fill it with tiny holes .20mm or .17mm apart -- ok, now try to pick it up and roughhandle it into the back of a curved sheet of glass, etc. Now that you've managed to get in place, imagine what happens when you "heat" it with an electron beam, over and over (i.e. it tends to warp). SONY, for one, has tried avoiding those problems by using alternative technology to implement their masks. Conceptually, they start with columns of ultra thin "wires" stretched across a metal frame in a jail-bar arrangement. (This has the extra benefit that the raster beam is sampled/filtered in the horizontal orientation only, but not in the vertical orientation.) They then add two tension wires in the horizontal direction to keep the frame from collapsing (if you look closely at a SONY CRTs you will notice the tension wires -- they look like a "one pixel wide dark line", and they are particularly easy to spot if you look at a "flat" area, with a homogenous color throughout -- if you want to irk TV salemen and the like, just stick your face up to the CRT and ask them, "what the heck is wrong with this TEEVEE? it's got a couple of them little lines missing!" :-) However, when, it gets past the .20mm pitch, SONYs technology poops out, too. That sounded like the end of the line for CRT technology, until Zenith changed things (yes, the _American_ company, and, no, they didn't do this research in Japan -- this is up and up American know-how). Zenith calls its technology the Flat Mask CRT, which conceptually is rather straight-forward (once they tell you about it): take the paper-thin mask, fill it with holes, and then glue it to the back of a sheet of glass! and that's it :-) Of course, the "sheet of glass" has to be optically flat, and that is no mean trick. Once you develop the technology to manufacture those things, however, the sky is the limit (easy for me to say): puch as many holes as you want in as thin a sheet of metal as you want (the thinner the better), then glue it to the glass sheet and you can let the American Tourister gorilla put it into the tube (i did preface this with the word "conceptually", didn't I?) Not only can you display a much higher resolution pictures that way, but you can also get a much higher contrast picture. The latter is a well known problem with spherical (or cylindrical for SONY) displays. Standard CRTs also have the problem that they catch reflections from around the room, while Zenith's Flat Mask eliminates that problem, too (ok, IF you stare into the CRT with your face levelled with it, AND you have a strong light shining on your face, THEN it will reflect on the display -- so, don't do that, which sounds unnatural anyway :-) Oh, yes. dots per inch, hey? /* Visible Lines Per Frame */ Horizontal_Sync_Rate = 78KHz; Vertical_Sync_Rate = 60Hz; 78KHz/60Hz => 1248 visible lines/frame + 52 lines/frame eaten up by the vertical retrace monster; Note also that if you want higher vertical refresh rates (an often heard goal/yearning/fad these days), you have to up your Horizontal Sync Rate just to retain your vertical resolution; Horizontal_Sync_Rate = 138KHz Vertical_Sync_Rate = 66Hz; /* a la Sun's */ 138KHz/66Hz => 2048 visible lines/frame + 47 lines/frame eaten up by the vertical retrace monster; moving that raster back and forth 138,000 times per second ain't easy; also pixel on-off time goes from 5.6 nsec/pixel to 2.9 nsec/pixel and theoretically that requires 350MHz DACs and video amps! /* "Holes" Per Line */ Line_Width (Active area) = 34.9 cm (13.75"); if(Pitch == .17mm) 34.9K/.17 => 2055 holes/line if(Pitch == .21mm) 34.9K/.21 => 1664 holes/line if(Pitch == .26mm) 34.9K/.26 => 1343 holes/line if(Pitch == .31mm) 34.9K/.31 => 1127 holes/line This if, of course, only partly true. To fully exploit the higher pitch CRT (and really get all those dots on the screen), you have to have an appropriately sized frame buffer behind it, AND the right Digital to Analog Converters (about 200MHz DACs for 1664X1248, and at least 350Mhz for a 2KX2K display, though 500MHz DACs are preferred!), AND the appropriate video amplifiers, etc. In addition, pitch is only one of the parameters: beam spot size is another. If you have a very small spot size (i.e. less than twice the pitch), you end up with lots of Moire patterns (look it up); if you have a very fat spot (i.e. more than three times the pitch), you end up with very soft images. Thus, the small spot size works better when displaying solids (i.e. sharper edges), while the fatter spots are better for displaying wire frames (i.e. less Moires). It gets worse (i.e. over my head) from there (beam optics, for one, are way beyond me). > > Are there any theoretical reason for LCD's to be more or less suitable than > CRT's for such high-resolution displays? (Is it even possible to make > multiple-color LCD's?) Thanks in advance for the enlightenment, > I don't know much about LCD masks. The idea here is to bypass the thin-mask-handling problem by encapsulating the mask "inside" two sheets of glass. You could conceivably change the mask dynamically to do windowing :-) All I know is that every time I've mentioned "LCD masks?" to people who know about these things, they make a face. And Tektronix, the most vociferous proponent of that technology, has not delivered anything yet (that I know of). From my vantage point (i.e. ignorance of the gory details), I say that Zenith's technology, though analog, is going to work better _sooner_ than the LCD, "digital" approach. The big question is "when" is Zenith going to bring this technology to the 19-inch, professional market? All I've heard so far (up to three months ago) is that they have plans to make .31mm CRTs in 14-inch format for the consumer market, and .20mm CRTs for the professional markets, but only in 14-inch format, and not in the 19-inch format. My guess is that making optically flat glass in that size sheets is not quite a piece of cake/possible. Time will tell, but I can't wait. ____________________________________________________ * Matt Perez * sun!cuba!mmp (415) 691-7544 DISCLAIMER: beisbole has bean bery, bery guud too me