Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!cs.utexas.edu!uunet!seismo!esosun!cogen!celerity!celit!hutch
From: hutch@celerity.uucp (Jim Hutchison)
Newsgroups: comp.graphics
Subject: Re: Color desktop scanners
Keywords: scanners
Message-ID: <421@celit.UUCP>
Date: 4 Aug 89 22:43:40 GMT
References: <1869@ucsd.EDU>
Sender: news@celerity.UUCP
Reply-To: hutch@celerity.UUCP (Jim Hutchison)
Organization: FPS Computing
Lines: 39

In <1869@ucsd.EDU> rich@net1.ucsd.edu (bmf) writes:
[...]
> 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.
Sets the footing as non-print quality scans, perhaps.  What kind of
resolution are we talking about here?  Drums range up to 3-4 digits
to the inch and are generally too large to put on desktops.

[...]
>	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.
How about using a different color scheme, such as YIQ.  N passes, based
on the response curves of your lights (3 in the case of YIQ).  Likely
this would give you shaky color passes and a good grey pass.  Now just
because YIQ is what's in NTSC doesn't mean that you have to use them
at low bandwidth like NTSC, the bandwidth of the I(cyan->red) and
Q(yellow->blue).  YIQ is designed around human vision, which also has
response curves like "overlapping upside down u's".  For a pleasant
bit of data on YIQ, see "Illumination and Color in Computer Generated
Imagery" by Roy Hall.

[...]
>	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.
I guess this could also be seen as a resolution limit?  Isn't this
more of an aperature problem?  I can see wanting a larger aperature
for a faster scan.  If you need the resolution/focus, couldn't you
just crank down the aperature for one or two of the passes?

/*    Jim Hutchison   		{dcdwest,ucbvax}!ucsd!celerity!hutch  */
/*    Disclaimer:  I am not an official spokesman for FPS computing   */