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<TITLE>sane-devel: Re: SnapScan</TITLE>
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<META NAME="Author" CONTENT="Stephen Williams (steve@icarus.com)">
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<H1>Re: SnapScan</H1>
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<STRONG>From:</STRONG> Stephen Williams (<A HREF="mailto:steve@icarus.com?Subject=Re:%20SnapScan&In-Reply-To=<200005050457.VAA20385@icarus.com>"><EM>steve@icarus.com</EM></A>)<BR>
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<STRONG>Date:</STRONG> Thu May 04 2000 - 21:57:39 PDT
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<LI><STRONG>Next message:</STRONG> <A HREF="0040.html">Louis van Dompselaar: "Re: SnapScan"</A>
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<LI><STRONG>Previous message:</STRONG> <A HREF="0038.html">Karl Heinz Kremer: "Re: SnapScan"</A>
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<A HREF="mailto:kluge@fujitsu.com.au?Subject=Re:%20SnapScan&In-Reply-To=<200005050457.VAA20385@icarus.com>">kluge@fujitsu.com.au</A> said:
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<BR>
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<EM>> That would make sense. Being a single-pass scanner, the R, G and B
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</EM><BR>
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<EM>> sensors can't possibly be in the same horizontal position, can they?
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</EM><BR>
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<P>Some of what I know about scanners... (we make scanners, FYI.)
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<BR>
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<P>They can, sorta. Linear color CCD arrays are usually three lines of CCD
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sensors with each line coated with a different color filter. Hence, they
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<BR>
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are often called tri-linear arrays. The sensor samples the width of the
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<BR>
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image all at once, then steps the sensor to the next position to get the
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next line of the image.
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<BR>
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<P>The sensors are offset vertically (that is perpendicular to scan direction)
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<BR>
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by some amount, but that is corrected by delaying the two earlier colors
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to match the latest color, or with optics. We usually use delays.
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<BR>
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<P>Color digital cameras use area arrays. That is, they have an area of
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<BR>
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pixels, like a TV screen in reverse, so that they can sample the whole
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scene at once. No need for that when taking a picture of a document in
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<BR>
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a transport or flat bed.
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<BR>
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<P>Colors can be offset by poor optics, because different colors can focus
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<BR>
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at different distances. Astronomers know all about achromatic optics.
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<BR>
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However, good, compact optics can be expensive, and that goes for scanner
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optics as well . I've seen so-called 1200DPI scanners that can't focus on
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<BR>
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a 150DPI feature. And colors can bleed by week electronics, too.
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<BR>
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<P>(Hell, the avision scanner right next to me claims to have 30bit color,
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<BR>
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that's 10 bits per color, but it saturates so badly that it can't really
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<BR>
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be getting better then 12bits, 4 bits per color, worth of significant
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precision.)
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<BR>
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<P>Anyhow, the above is a bit of a simplification, but you get the idea.
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<BR>
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<PRE>
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--
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Steve Williams "The woods are lovely, dark and deep.
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<A HREF="mailto:steve@icarus.com?Subject=Re:%20SnapScan&In-Reply-To=<200005050457.VAA20385@icarus.com>">steve@icarus.com</A> But I have promises to keep,
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<A HREF="mailto:steve@picturel.com?Subject=Re:%20SnapScan&In-Reply-To=<200005050457.VAA20385@icarus.com>">steve@picturel.com</A> and lines to code before I sleep,
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<A HREF="http://www.picturel.com">http://www.picturel.com</A> And lines to code before I sleep."
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<P><P><P>--
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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:%20SnapScan&In-Reply-To=<200005050457.VAA20385@icarus.com>">majordomo@mostang.com</A>
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</PRE>
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<LI><STRONG>Next message:</STRONG> <A HREF="0040.html">Louis van Dompselaar: "Re: SnapScan"</A>
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<LI><STRONG>Previous message:</STRONG> <A HREF="0038.html">Karl Heinz Kremer: "Re: SnapScan"</A>
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<LI><STRONG>In reply to:</STRONG> <A HREF="0037.html">Steffen Kluge: "Re: SnapScan"</A>
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<LI><STRONG>Next in thread:</STRONG> <A HREF="0040.html">Louis van Dompselaar: "Re: SnapScan"</A>
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<LI><STRONG>Next in thread:</STRONG> <A HREF="0038.html">Karl Heinz Kremer: "Re: SnapScan"</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 May 04 2000 - 21:59:17 PDT</EM>
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