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- Newsgroups: comp.graphics
- Path: sparky!uunet!mcsun!ieunet!tcdcs!vax1.tcd.ie!rjbolger
- From: rjbolger@vax1.tcd.ie
- Subject: Re: 24bit > 8bit Display Question
- Message-ID: <1992Aug14.115842.1@vax1.tcd.ie>
- Lines: 40
- Sender: usenet@cs.tcd.ie (NN required at ashe.cs.tcd.ie)
- Nntp-Posting-Host: vax1.tcd.ie
- Organization: Trinity College Dublin
- References: <BssDHt.19u@news.cso.uiuc.edu>
- Date: Fri, 14 Aug 1992 11:58:42 GMT
- Lines: 40
-
- In article <BssDHt.19u@news.cso.uiuc.edu>, pgrg9345@uxa.cso.uiuc.edu (pAul rAdja ) writes:
- > Question: I need to be able to display a 24bit image on a
- > pc that only has an 8bit look-up table. Does anyone know of a
- > good way or reference on how to optimally fill the
- > table up? Speed is a strong consideration in my problem.
-
- For a quick way of displaying 24 bit images on a 256 color display
- with good quality, you can tradeoff screen resolution for extra
- depth.
-
- First generate a palette of three colour ramps of r,g & b, with g & b
- going from 0 to 63 in intensity and r going from 0 to 31. Then plot
- each image pixel using four screen pixels as such:
- _____________________
- | | |
- | Red | Green |
- |---------------------|
- | | |
- | Blue | Red |
- |---------------------|
-
- This works surprisingly well giving a '17' bit display but only at
- resolutions greater than 320x200. I'm lucky enough to have a 1MB
- Trident card that gives 1024x768 resoloution, and using this technique
- I get an apparent res of 512x384 which is good enough for my needs.
-
- You can try other combinations such as three screen pixels per image
- element, but this introduces artifacts in the image. Using Red twice
- and halving its intensity was the best combination that I could find.
-
- The drawback with this method is that the image is displayed at a low
- intensity because only 1/3 of the screen guns are switched on, but the
- overall quality is really quite good.
-
- Hope this helps, but if you need any more info contact me through E-mail.
-
- Regards,
- * Richard Bolger *
- Richard. * Trinity College Dublin *
- * Rjbolger@vax1.tcd.ie *
-