Path: utzoo!utgpu!watmath!att!ucbvax!ucsd!net1.ucsd.edu!rich
From: rich@net1.ucsd.edu (bmf)
Newsgroups: comp.graphics
Subject: Color desktop scanners (a technical discussion begins)
Message-ID: <1869@ucsd.EDU>
Date: 29 Jul 89 00:33:29 GMT
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Reply-To: rich@net1.ucsd.edu (bmf)
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 I have written software for color desktop scanners for about three
 years. In that time I have yet to see one that I really feel
 positive about. Most of them have some good points but... 

 Anyway this discussion is for hobby purposes. The software I write
 for a living but the hardware a do at home for fun like any Buckaroo B.
 fan.

 Problem: 
	Creating a desktop color scanner which is easy to use, has
	the quality of a drum scanner , and costs less than $3000 in
	parts. If we keep the discussion public we all gain a public
	domain scanner.

 Todays Scanners
	Todays scanners rely on either CCD arrays or video chips to
	collect a scan line, or block of pixel data. Both of these
	devices suffer from dynamic range problems. Determining black 
	and white on them isn't that bad but getting a linear
	response is. Maybe a different technology should be applied
	here.

	Both of these devices need to be moved around the image (or the
	image moved around device)  This means adapting some sort of
	stepper motor technology. This leads a loss of sharpness in
	the image. Some companies handle it better than others, but
	again maybe a different sort of solution is avaiable.
	Software solutions tend to be slow and make an image more
	crisp rather than match the original.

	The CCD technology relies on either color light bulbs or
	color filters to reproduce the color in the image. Nasty
	problems occur here. The spectral response of both the
	filters and the bulbs tend to look like overlapping upside
	down u's. So if you are using red, green, and blue filters,
	there are certain reds greens and blues which do not
	register at all. While there are some greens that come
	register as yellow and others that register as cyan. So a
	green grass may effectively dither out to a grey. (this
	really pisses off scanner salespeople if you scan an image
	like this in front of them at a trade show.)

	Both the CCDs and the Video chips rely on camera lenses to
	focus the image unfortunately a red, green, and blue light
	have different focal lengths, so again we have a small
	sharpness problem.

 Conclusion:
	You can do a good job with todays scanners but what about
	applying some other technologies. Are there CD lasers
	available in a variety of wavelengths? How about focusing
	one of the spectral analysis devices onto a ccd array and
	any diode which shows a response gets added into the color
	value of the current pixel being scanned (too slow huh?).
	This could be fun.


	-Rich

/*    Rich Stewart   		{dcdwest,ucbvax}!ucsd!net1!rich  */