Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!ncar!tank!uxc!uxc.cso.uiuc.edu!uxg.cso.uiuc.edu!uxe.cso.uiuc.edu!mcdonald From: mcdonald@uxe.cso.uiuc.edu Newsgroups: comp.graphics Subject: Re: ShowScan quality image bit rate Message-ID: <46900028@uxe.cso.uiuc.edu> Date: 5 Feb 89 18:43:00 GMT References: <18071@glacier.STANFORD.EDU> Lines: 37 Nf-ID: #R:glacier.STANFORD.EDU:18071:uxe.cso.uiuc.edu:46900028:000:1997 Nf-From: uxe.cso.uiuc.edu!mcdonald Feb 5 12:43:00 1989 >Someone else commented that at some point you'd exceed the limits >of human perception. Sorry if this is redundant, but here are some >numbers worth thinking about. >2 eyes x 1,000,000 optic nerve fibres x 200 spikes/sec peak firing rate > = 0.4 gigabits/sec >These figures are approximate, but it's the right order of magnitude. That may be true, but it is irrelevent for general purpose displays, films, photography, etc. The point is that a the eye has much better abilities at the center of the field that at the edges. But, for a general purpose display, you need to have the same resolution all across it, as the viewer can move his eyes to look at various places. Hence you need a lot more bits than the eye uses. How much more is the interesting question. Let's see - the eye has a resolution of about 1 minute of arc. Lets say you want a display which is one meter square. I would like to view it at a distance of 0.7 meter. 0.7 meter / (57degrees per radian * 60 minutes per degree) = 0.2 millimeter. That is 25,000,000 resolution elements. In the simplest case (each element can have any color, 256 levels per three primaries) you need 24 bits per element . That is 600 megabits per static picture. The question of the number of independent frames per second is tougher, but let's say 15 per second minimum - that gives 9 gigabits per second. Make it ten gigabits for a round number. If done right that wouldn't flicker but motion would appear jerky at that rate, unless "smearing" were done on the individual frames. But that smearing wouldn't effect the bit rate, which would remain at 10 Gbits. Then one might try to reduce the color resolution in small areas, perhaps gettig down to 3 gibabits per second. That's 10 times more than the 0.4 gbit per second quoted above, and sounds reasonable, given the ratio that such a display would cover compared to the region of good vision of the eye. Now, lets have a 4 pi steradian display - thats 10 times more than the above!