Path: utzoo!utgpu!watserv1!watmath!att!rutgers!apple!vsi1!zorch!xanthian From: xanthian@zorch.SF-Bay.ORG (Kent Paul Dolan) Newsgroups: comp.sys.amiga Subject: Re: 24/32 Bit Color Message-ID: <1990Oct18.022203.28139@zorch.SF-Bay.ORG> Date: 18 Oct 90 02:22:03 GMT References: <33786@nigel.ee.udel.edu> Organization: SF-Bay Public-Access Unix Lines: 34 In article <33786@nigel.ee.udel.edu> byrne@muppet.dnet.ge.com writes: >I think I need some education. I was under the (false?) assumption that the >human eye could not distinguish 16 million colors (24 bit). I assumed 24 bits >was decided as number because it was an even multiple of a byte given the 3 >color components (RGB). Since most displays don't have 16 million pixels, this >gives you a great big palette. But why 32 bit? Is 32 bit color used because >it is the word size of most of the popular high performance microprocessors >(i.e 68020+)? I don't see it buying you anything from a color stand point >because who could distinguish adjacent colors from either 24 or 32 bit >palettes? Does it help in shading or is it just for data movement speed? >Seems like overkill. Thanks, > > -FB Well, color starts to get pretty subtle at 7 bits per gun, but some people can still see Mach bands (a kind of color artifact) in 7/21 bit color, so mostly the human eye is described as having about 7.5 bits of color sensitivity; some folks need 7, some need 8 bits. As to 32 bits, most implementations that use bits beyoond 24 either use the extra bits for overlay line graphics that don't mess with the underlying color, or else for "alpha" data, a kind of "percent of pixel in use" item that lets some really nice translucency effects be done when images are overlaid on one another in composite pictures. Implementations using at least 48 bits are in common use in high end systems. I forgot -- a third use is to store z-buffer distance in the extra bits, to allow painter's algorithm to work, though in this case, 8 extra bits is probably not enough. If that wasn't clear enough, send email and I'll try harder; I'm listening to the Series with most of my attention -- fifth inning, 4-3 A's, just now. Kent, the man from xanth.