taab5@isuvax.iastate.edu (Marc Barrett) (06/17/91)
While browsing through a recent issue of Computer Shopper, I came across an ad for something that looks interesting at the very least. The ad is for an ordinary VGA card that comes equipped with something called the "Edsun CEG DAC". From the ad, this replacement DAC chip gives VGA cards a resolution of 2048x1536 and 700,000+ colors "on a standard VGA monitor." My question is, how can something like this possibly be achieved on a standard VGA monitor, and with ordinary VGA cards with 1M of video RAM? This thing is obviously some sort of anti-aliasing hack, but I'd like some information on how this thing works. ------------------------------------------------------------- / Marc Barrett -MB- | BITNET: XGR39@ISUVAX.BITNET / / ISU COM S Student | Internet: XGR39@CCVAX.IASTATE.EDU / ------------------------------------------------------------ \ The great thing about standards is that / \ there are so many of them to choose from. / -------------------------------------------------------
kdarling@hobbes.catt.ncsu.edu (Kevin Darling) (06/17/91)
> [...] an ordinary VGA card that comes equipped with something called the > "Edsun CEG DAC". From the ad, this replacement DAC chip gives VGA cards > a resolution of 2048x1536 and 700,000+ colors "on a standard VGA monitor." > [CEG=Continuous Edge Graphics, btw - kd] > My question is, how can something like this possibly be achieved on a > standard VGA monitor, and with ordinary VGA cards with 1M of video RAM? The CEG/DAC is a replacement palette chip which allows tricks such as blending adjacent pixel colors and updating palette values on the fly. This is done by setting aside some of the normal 256 colors as commands. The 700,000 colors is true enough... at least in a similiar manner to claiming 4096 colors in HAM mode: it can take an extra pixel or more to switch (altho the method is totally different and fairly clever). I think that the 2048x1536 resolution claim is ad hype tho. See, the idea is that all those extra colors can make a stock 1024x768 card look like it has the "resolution" of a larger display. Well, sure, but compared to what? A _true_ 2048x1536 700,000-color card would look even better :-). For more information, see ohhh, Dr Dobb's Journal - April 1991, pgs 133+. Personally, I'm not sure how much programming will be done for them now that the Tseng 15-bit color cards are getting popular. Hard to say yet. The CEG will be able to display some incredible pictures and animations. In any case, sounds like a question for comp.graphics or the ibm groups? kevin <kdarling@catt.ncsu.edu>
daveh@cbmvax.commodore.com (Dave Haynie) (06/18/91)
In article <1991Jun17.103306.29343@news.iastate.edu> taab5@isuvax.iastate.edu writes: > While browsing through a recent issue of Computer Shopper, I came across >an ad for something that looks interesting at the very least. The ad is >for an ordinary VGA card that comes equipped with something called the >"Edsun CEG DAC". From the ad, this replacement DAC chip gives VGA cards >a resolution of 2048x1536 and 700,000+ colors "on a standard VGA monitor." Well, you know what they say about believing what you read. This is essentially a RAMDAC with some special modes. It's doing the same kind of tricks HAM does, though not exactly the same way HAM does it. All modes trade a few color registers for special functions. First of all, you start out at power up time, the device is in normal everyway VGA color lookup mode. You can kick it into one mode that lets you reprogram color registers on the fly, a little bit as if you had a copper. The chip finds a special color value, and instead of going to the CLUT, it holds the color from the last CLUT fetch. After that value, the next 4 pixel values give you the new CLUT register number and the color to put there. So, if you can live with a color not changing for five pixels, you can reprogram one CLUT value. Another mode (actually I think there are a couple of versions of this) lets you interpolate between color values. You kick the display with another magic value. Instead of picking a CLUT entry, you're kicked into interpolation mode. The next pixel value has your ending color (the starting color being the last displayed, which is also displayed for the magic cookie pixel). Then you get to fetch new magic cookie pixels, which get expressed as a percentage of the starting pixel versus the ending pixel. Basically, these new modes, like HAM, need a degree of precompilation and clever color allocations to be useful, but when done right, they produce images that look better than the underlying bit depth would imply. Any claims of "2048x1536" pixels are, of course, lies. -- Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy "This is my mistake. Let me make it good." -R.E.M.
peterk@cbmger.UUCP (Peter Kittel GERMANY) (06/18/91)
In article <1991Jun17.103306.29343@news.iastate.edu> taab5@isuvax.iastate.edu writes: > > The ad is >for an ordinary VGA card that comes equipped with something called the >"Edsun CEG DAC". From the ad, this replacement DAC chip gives VGA cards >a resolution of 2048x1536 and 700,000+ colors "on a standard VGA monitor." > > My question is, how can something like this possibly be achieved on a >standard VGA monitor, and with ordinary VGA cards with 1M of video RAM? >This thing is obviously some sort of anti-aliasing hack, but I'd like >some information on how this thing works. This chip is a normal DAC with built-in CLUT (color lookup table), as it is common on VGA cards. So it is compatible with existing designs. But it has the added capability to interpolate the colors between two horizontal pixels in much finer color resolution. You give it certain fake color values that are really control values and it makes a smooth interpolation between two pixels. This way you can anti-alias very well. Yet there *is* an overhead in setting up these control values. I heard there are already drivers for standard Windows 3.0 available, but they are *really* slow, though the result seems to be remarkable. So, you perhaps should forget about animation with this. You have a situation similar to HAM, in that you can easily draw one single line in this mode on the screen, but get into difficulties, if you want to draw another line in different color that crosses the first one at some angle. So also here you have not only an organisational overhead, but also some limitations to consider. And the drawing programs yet have to consider this additional feature. I guess this part could also be used on the Amiga in hacks like DCTV or HAM-E, but it sure would remain a hack. -- Best regards, Dr. Peter Kittel // E-Mail to \\ Only my personal opinions... Commodore Frankfurt, Germany \X/ {uunet|pyramid|rutgers}!cbmvax!cbmger!peterk