James_Hastings-Trew@tptbbs.UUCP (James Hastings-Trew) (03/13/91)
In a message dated Tue 12 Mar 91 04:50, Harvey_taylor@mindlink.uucp (harvey wrote: H> Background: I want to display some large 256 level greyscale H> video samples. The standard Amiga will output only 16 levels. H> So, I am trying to figure out the best way to increase the number of H> greyscale levels viewable on the (my) Amiga. So far the candidates H> are: H> 1) Dithering H> 2) GreyScale to HAM [SHAM, SHAMM, Dynamic whatever] H> 3) A colour board A 24 bit colour card should be able to give you a true 256 grey scale picture. Other than than, you best bet is dithering - HAM and Dynamic modes don't alter the palette available, so still only have 16 greys to work with in those modes. The Art Department does a very nice job of converting 256 greyscale images to 16 greys with Floyd-Steinberg dithering. I daresay at hi-res interlace, the results would be indistinguishable from real 256 grey once you get it into video.
raible@cbmvax.commodore.com (Bob Raible - LSI Design) (03/14/91)
In article <James_Hastings-Trew.2800@tptbbs.UUCP> James_Hastings-Trew@tptbbs.UUCP (James Hastings-Trew) writes: >In a message dated Tue 12 Mar 91 04:50, Harvey_taylor@mindlink.uucp (harvey >wrote: > > > H> Background: I want to display some large 256 level greyscale > H> video samples. The standard Amiga will output only 16 levels. > > H> So, I am trying to figure out the best way to increase the number of > H> greyscale levels viewable on the (my) Amiga. So far the candidates > H> are: > > H> 1) Dithering > H> 2) GreyScale to HAM [SHAM, SHAMM, Dynamic whatever] > H> 3) A colour board > > >A 24 bit colour card should be able to give you a true 256 grey scale >picture. Other than than, you best bet is dithering - HAM and Dynamic modes >don't alter the palette available, so still only have 16 greys to work with >in those modes. > >The Art Department does a very nice job of converting 256 greyscale images to >16 greys with Floyd-Steinberg dithering. I daresay at hi-res interlace, the >results would be indistinguishable from real 256 grey once you get it into >video. I was was wondering if some software type could check out a theory of mine. I was thinking that if one twiddled with the lsb's of the 3 guns one could create more useable greyscales than 16,colors like RGB=778,788,889,899, etc. One probably notice any chroma artifacts for many of these shades. Anybody want to give it a whirl. I'd oblige, but I haven't programmed anything since my undergraduate days(BSEE '77).
spence@cbmvax.commodore.com (Spencer Shanson) (03/27/91)
In article <19847@cbmvax.commodore.com> raible@cbmvax.commodore.com (Bob Raible - LSI Design) writes: >mine. I was thinking that if one twiddled with the lsb's of the 3 guns >one could create more useable greyscales than 16,colors like >RGB=778,788,889,899, etc. One probably notice any chroma artifacts for >many of these shades. Anybody want to give it a whirl. I'd oblige, but I >haven't programmed anything since my undergraduate days(BSEE '77). > Bob, I tried this a few years ago with some Scanner s/w I wrote (I could bring it in a nd show you). I wouldn't recommend it as a way of increasing the grey sscales though - the tinting is fairly noticeable. -- --------------------------------------------------------------------------- Spencer Shanson - Amiga Software Engineer | email: spence@commodore.COM | or uunet!cbmvax!spence All opinions expressed are my own, and do not | "You know my methods. Apply (necessarily) represent those of Commodore. | them" -- Sir Arthur Conan | Doyle - 'The Sign of Four'
chrisg@cbmvax.commodore.com (Chris Green) (03/27/91)
In article <20129@cbmvax.commodore.com> spence@cbmvax.commodore.com (Spencer Shanson) writes: >Bob, I tried this a few years ago with some Scanner s/w I wrote (I could bring >it in a nd show you). I wouldn't recommend it as a way of increasing the >grey sscales though - the tinting is fairly noticeable. > It does work pretty well when you have a bit more color resolution, though. I've got a great 256 grey-scale palette for the VGA (normally only 64 grey scales) that uses this trick.