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<TITLE>sane-devel: Re: Scanner Color Shift Problem</TITLE>
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<META NAME="Author" CONTENT="Steve Underwood (steveu@coppice.org)">
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<META NAME="Subject" CONTENT="Re: Scanner Color Shift Problem">
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<H1>Re: Scanner Color Shift Problem</H1>
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<!-- received="Thu Mar 1 18:53:11 2001" -->
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<!-- name="Steve Underwood" -->
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<!-- subject="Re: Scanner Color Shift Problem" -->
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<!-- id="3A9F0F17.6203DA58@coppice.org" -->
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<STRONG>From:</STRONG> Steve Underwood (<A HREF="mailto:steveu@coppice.org?Subject=Re:%20Scanner%20Color%20Shift%20Problem&In-Reply-To=<3A9F0F17.6203DA58@coppice.org>"><EM>steveu@coppice.org</EM></A>)<BR>
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<STRONG>Date:</STRONG> Thu Mar 01 2001 - 19:10:15 PST
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<P>
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<LI><STRONG>Next message:</STRONG> <A HREF="0027.html">David Gesswein: "Re: Scanner Color Shift Problem"</A>
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<UL>
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<LI><STRONG>Previous message:</STRONG> <A HREF="0025.html">Davis, Tom: "RE: Writing Fujitsu M3091 backend"</A>
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<LI><STRONG>In reply to:</STRONG> <A HREF="0011.html">Frederik Ramm: "Scanner Color Shift Problem"</A>
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<LI><STRONG>Next in thread:</STRONG> <A HREF="0027.html">David Gesswein: "Re: Scanner Color Shift Problem"</A>
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<LI><STRONG>Reply:</STRONG> <A HREF="0027.html">David Gesswein: "Re: Scanner Color Shift Problem"</A>
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<LI><STRONG>Reply:</STRONG> <A HREF="0030.html">Frederik Ramm: "Re: Scanner Color Shift Problem"</A>
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<P>
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Frederik Ramm wrote:
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<BR>
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<EM>>
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</EM><BR>
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<EM>> Hi,
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</EM><BR>
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<EM>>
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</EM><BR>
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<EM>> at first I thought it was a problem with the driver I'm writing but
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</EM><BR>
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<EM>> the Windows driver didn't deliver any better results. When scanning in
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</EM><BR>
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<EM>> color at the highest resolution (300x600dpi), black letters on a white
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</EM><BR>
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<EM>> background exhibit a green "shadow" to one side and a red "shadow" to
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</EM><BR>
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<EM>> the other. The shadow is about 3-4 pixels high. I've put an example
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</EM><BR>
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<EM>> here:
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</EM><BR>
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<EM>>
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</EM><BR>
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<EM>> <A HREF="http://www.remote.org/frederik/tmp/gap8.ppm">http://www.remote.org/frederik/tmp/gap8.ppm</A>
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</EM><BR>
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<EM>>
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</EM><BR>
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<EM>> You'll have to magnify the window to see it clearly.
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</EM><BR>
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<P>This looks like a common colour merging problem. In most scanners there
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<BR>
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is a physical separation between the red green and blue sensors. Most
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<BR>
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scanners just feed data to the host with this separation, and the driver
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<BR>
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needs to shuffle the scan lines to accurately merge the colours. You
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<BR>
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will find code to perform this function in several sane backends. A
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<BR>
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typical offset between each sensor row is 1/75 inch, but varies between
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<BR>
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models.
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<BR>
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<P>In your example scan, the physical shift looks quite small. It looks
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<BR>
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like the software is attempting to merge the colours, but doesn't use
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<BR>
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the correct physical offset.
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<BR>
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<P><EM>> I would be very happy if someone who is a bit more experienced with
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</EM><BR>
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<EM>> scanners than I am could look at this and tell me if this would be
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</EM><BR>
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<EM>> considered "normal" in a medium-priced scanner (Fujitsu M3091, ca.
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</EM><BR>
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<EM>> USD 800) or if I that should be considered a fault in this specific
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</EM><BR>
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<EM>> model and I should send it back to the shop for an exchange?
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</EM><BR>
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<P>Today an $800 scanner is hardly mid range - its a rather expensive
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<BR>
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scanner. Even a $50 scanner usually merges the colours well enough that
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<BR>
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colour fringing is very hard to detect.
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<BR>
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<P>Regards
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<BR>
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Steve
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<BR>
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<P><PRE>
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--
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Source code, list archive, and docs: <A HREF="http://www.mostang.com/sane/">http://www.mostang.com/sane/</A>
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To unsubscribe: echo unsubscribe sane-devel | mail <A HREF="mailto:majordomo@mostang.com?Subject=Re:%20Scanner%20Color%20Shift%20Problem&In-Reply-To=<3A9F0F17.6203DA58@coppice.org>">majordomo@mostang.com</A>
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</PRE>
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<!-- next="start" -->
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<LI><STRONG>Next message:</STRONG> <A HREF="0027.html">David Gesswein: "Re: Scanner Color Shift Problem"</A>
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<LI><STRONG>Previous message:</STRONG> <A HREF="0025.html">Davis, Tom: "RE: Writing Fujitsu M3091 backend"</A>
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<LI><STRONG>In reply to:</STRONG> <A HREF="0011.html">Frederik Ramm: "Scanner Color Shift Problem"</A>
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<!-- nextthread="start" -->
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<LI><STRONG>Next in thread:</STRONG> <A HREF="0027.html">David Gesswein: "Re: Scanner Color Shift Problem"</A>
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<LI><STRONG>Reply:</STRONG> <A HREF="0027.html">David Gesswein: "Re: Scanner Color Shift Problem"</A>
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<LI><STRONG>Reply:</STRONG> <A HREF="0030.html">Frederik Ramm: "Re: Scanner Color Shift Problem"</A>
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<EM>
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This archive was generated by <A HREF="http://www.hypermail.org/">hypermail 2b29</A>
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: <EM>Thu Mar 01 2001 - 18:54:04 PST</EM>
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