Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!sgi!tarolli@westcoast.esd.sgi.com
From: tarolli@westcoast.esd.sgi.com (Gary Tarolli)
Newsgroups: comp.sys.sgi
Subject: Re: Who needs 24 bit colors
Summary: 8 bits of RGB
Message-ID: <95453@sgi.sgi.com>
Date: 4 Apr 91 18:19:51 GMT
References: <9104032223.AA03789@karron.med.nyu.edu>
Sender: guest@sgi.sgi.com
Organization: Silicon Graphics, Inc., Mountain View, CA
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In article <9104032223.AA03789@karron.med.nyu.edu>, Dan Karron@UCBVAX.BERKELEY.EDU writes:
> 
> If you are dithering about colors and bits, here is an interesting piece from
> Photonics Spectra, April 1991, Page 119.
> 
> Essentialy, the author, Kendal Preston, Jr. argues that we don't need more than
> 8 bits of color info, and by doing histogram analysis of a medical photomicro-
> graph of stained cells shows that most of the histogram bins are empty, and
> that dynamic data compression is possible by using a color map with various
> criteria to assign a color to a color values with a high frequency.
> 
> I don't agree that we should not consider >8 bit in color
> workstation design, and we should consider that his scanner may not
> have the dynamic range resolution to more evenly fill the color distribution
> of his scanned images.
> 
> What do you think?
> 

I agree that for his pictures 8 bits (256 arbitrary colors) is probably enough.
When you get to select the 256 colors you are going to dither with, you can
get very good results.  Even if you work from a fixed pallete you can get
decent results.

The problems are:
	1) not all pictures will have many empty bins, I have no proof of
		this or experience with this, but I have to believe there
		exists pictures (like colorwheels) that have few empty bins
	2) If you only have 1 256 entry color lookup table and you are in a
		windowed environment, how do you choose/vary the table as
		many different pictures (both scanned and geometric) are
		displayed.  If you chose a fixed palette you can get decent
		results, but it wont please everyone.
	3) there are always those people doing very precise color work who
		wont settle for anything less than 24 bits.

and I agree, if his scanner was flaky or inaccurate in the least, it could
invalidate all his results.


--------------------
	Gary Tarolli