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<TITLE>sane-devel: UMAX transparency adapter / averaging</TITLE>
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<META NAME="Author" CONTENT="Marko Cebokli (s57uuu@hamradio.si)">
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<META NAME="Subject" CONTENT="UMAX transparency adapter / averaging">
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<H1>UMAX transparency adapter / averaging</H1>
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<!-- name="Marko Cebokli" -->
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<!-- subject="UMAX transparency adapter / averaging" -->
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<STRONG>From:</STRONG> Marko Cebokli (<A HREF="mailto:s57uuu@hamradio.si?Subject=Re:%20UMAX%20transparency%20adapter%20/%20averaging&In-Reply-To=<3A3372C5.6885A468@hamradio.si>"><EM>s57uuu@hamradio.si</EM></A>)<BR>
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<STRONG>Date:</STRONG> Sun Dec 10 2000 - 04:10:45 PST
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<LI><STRONG>Next in thread:</STRONG> <A HREF="0103.html">Oliver Rauch: "Re: UMAX transparency adapter / averaging"</A>
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<P>
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Hello!
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<BR>
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<P>These ae some of my observations (and wishes) concernig the
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<BR>
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transparency adapter for the UMAX Astra 1220S.
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<BR>
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<P>When I scan a normally exposed slide, it comes out quite dark, and
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<BR>
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I must stretch the histogram in XSANE (GAMA=1.3 B=120 C=120 for example)
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<BR>
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This causes 'holes' in the output histogram (the dark values go 0, 7,
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<BR>
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11, 15...). So it may be desirable to scan internally with 12
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<BR>
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bits/color, even if the output is only 8 bits - to provide 'meat' for
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<BR>
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histogram stretching.
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<BR>
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<P>Also, the dark areas tend to be quite noisy (same with twain/win).
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<BR>
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It seems this is the CCD / readout electronics / AD converter noise.
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<BR>
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Increasing the exposure time would help here (in the dark areas) but
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<BR>
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would probably cause overflow in the bright pixels.
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<BR>
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What I do now is to scan the same slide several times and average
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<BR>
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the scans later in the application program. The results are well
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<BR>
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worth the extra work!
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<BR>
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<P>So, I would like this averaging done in the SANE backend, like the
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<BR>
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NIKON super coolscan 2000 (LS 2000) film scanner does it.
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<BR>
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Again, this could be done with more bits internally. Actually, such
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<BR>
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averaging can give you more bits of (real!) resolution than your A/D
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<BR>
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has.
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<BR>
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<P>Tha averaging could be done two ways:
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<BR>
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<P>1. at each scanhead position take several readings and average them
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<BR>
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before moving the scanhead on.
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<BR>
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<P>2. run several full scans (running the scanhead back and forth across
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<BR>
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the scan area). (smpling only when moving forward)
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<BR>
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<P>This second way may seem stupid, since it needs more memory and the
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<BR>
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mechanism inacuracies will reduce the spatial resolution, but it has
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<BR>
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one nice property: because each scan is done at a slightly different
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<BR>
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position, the film grain will average out.
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<BR>
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I have found this to have a much better grain supression/resolution loss
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<BR>
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ratio than simply using a low-pass (blur) filter on a single scan.
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<BR>
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<P><P>Marko Cebokli
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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:%20UMAX%20transparency%20adapter%20/%20averaging&In-Reply-To=<3A3372C5.6885A468@hamradio.si>">majordomo@mostang.com</A>
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</PRE>
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<LI><STRONG>Next in thread:</STRONG> <A HREF="0103.html">Oliver Rauch: "Re: UMAX transparency adapter / averaging"</A>
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