Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!masscomp!calvin!mark From: mark@calvin..westford.ccur.com (Mark Thompson) Newsgroups: comp.sys.amiga.graphics Subject: Re: 24bit display questions Message-ID: <62174@masscomp.westford.ccur.com> Date: 27 Jun 91 19:43:43 GMT References: <1991Jun21.134816.10190@uokmax.ecn.uoknor.edu> <62170@masscomp.westford.ccur.com> <1991Jun26.175454.26359@cbnewsd.att.com> <22723@cbmvax.commodore.com> Sender: news@masscomp.westford.ccur.com Reply-To: mark@calvin.westford.ccur.com (Mark Thompson) Distribution: usa Organization: Concurrent Computer Corp. Westford MA. Lines: 32 raible@cbmvax.commodore.com (Bob Raible - LSI Design) writes: >rcj2@cbnewsd.att.com (ray.c.jender) writes: >> I thought I had a basic understanding of this 24bit business. >> Using ToasterPaint, if you paint in HAM mode (which is 12 bit, right?), >> then render it to the Toaster it becomes 24bit. What happens to >> the other 12 bits? How do you get 24bit out of 12bit???? >> 12bit is 4096 colors. 24bit is 16million colors. Are the left-over >Someone please correct me if I'm wrong, but Toaster internal data is not >24bit RGB but rather 16 bit digitized composite. The latter is much more >efficient for a box that lacks RGB outputs. The use of HAM mode is a >compromise dictated by the underlying AMIGA graphics hardware. Yes, the Toaster 'frame' format (which I am nearly certain is the format used internally by the hardware) is not in RGB color space but in a 4:2:2 chroma/luma format akin to YUV video. The 4:2:2 represents the sample rate for luminance, chrominance axis 1, and chrominance axis 2 respectively. Each of the three channels are digitized to 8 bit precision (as in 24bit RGB) but since the two chroma channels are at half the sample rate of the luma, the data fits into a 16 bit quantity. Sampling chroma at a frequency equal to luma is unecessary because the extra information would be lost in the composite video output. If you were to take a 24bit IFF and save it in Toaster frame format and then convert it back to 24bit IFF, the colors will bleed past their original boundries when viewed on an RGB frame buffer. DCTV uses a similar approach except its sample rate is half that of the Toaster, hence the degredation in quality. %~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~% % ` ' Mark Thompson CONCURRENT COMPUTER % % --==* RADIANT *==-- mark@westford.ccur.com Principal Graphics % % ' Image ` ...!uunet!masscomp!mark Hardware Architect % % Productions (508)392-2480 (603)424-1829 & General Nuisance % % % ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~