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From: raveling@isi.edu (Paul Raveling)
Newsgroups: comp.graphics
Subject: Re: COLOR SCANNING.
Message-ID: <11011@venera.isi.edu>
Date: 16 Dec 89 01:20:13 GMT
References: <3184@com50.C2S.MN.ORG> <13428@s.ms.uky.edu>
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Reply-To: raveling@isi.edu (Paul Raveling)
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In article <3184@com50.C2S.MN.ORG>, chris@com2serv.C2S.MN.ORG (Chris
Johnson) writes:
> 
> Maybe this goes without saying in this newsgroup, but 24 bits of color
> value for RGB might be called near photographic quality, as far as color
> rendition goes, but 5 bits (32 levels) probably is not very close.

	It depends a lot on the image.  For most images 5 or 6 bits
	is about the threshold where a casual viewer won't notice
	the difference when comparing them with any higher number
	of levels.  On the extremes, there are a few images
	where this is true at 4 bits, and relatively more that need
	about 8 bits or more.

	I can also believe reports that some images improve when viewed
	with 30 or 36 bits rather than 24, because human perception
	is highly sensitive to differences in color rather than absolute
	color.  I suspect that it might be possible to quantize images
	to perhaps 10-12 bits and get the same effect; we're limited
	a bit by hardware what usually shows either 24-bit unquantized
	color or at most 8-bit quantized color.

> And that's only color rendition.  Even a 400dpi image is not remotely
> close to photographic quality in resolution.

	Most people swear my 100 dpi monitor produces photographic
	quality resolution.  In truth it doesn't, but usually the
	mind of the viewer does.

	In fact it's fun to occasionally use a magnifier window
	to demonstrate to people that some of the detail they see
	doesn't exist in the image, but rather is synthesized in their
	brain based on some subtle cues that do exist.


----------------
Paul Raveling
Raveling@isi.edu