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<H1>Re: UMAX transparency adapter / averaging</H1>
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<STRONG>From:</STRONG> Oliver Rauch (<A HREF="mailto:oliver.rauch@Wolfsburg.DE?Subject=Re:%20UMAX%20transparency%20adapter%20/%20averaging&In-Reply-To=&lt;3A33A2AA.79F88581@wolfsburg.de&gt;"><EM>oliver.rauch@Wolfsburg.DE</EM></A>)<BR>
<STRONG>Date:</STRONG> Sun Dec 10 2000 - 07:35:06 PST
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Marko Cebokli wrote:
<BR>
<EM>&gt;
</EM><BR>
<EM>&gt; Hello!
</EM><BR>
<EM>&gt;
</EM><BR>
<EM>&gt; These ae some of my observations (and wishes) concernig the
</EM><BR>
<EM>&gt; transparency adapter for the UMAX Astra 1220S.
</EM><BR>
<EM>&gt;
</EM><BR>
<EM>&gt; When I scan a normally exposed slide, it comes out quite dark, and
</EM><BR>
<EM>&gt; I must stretch the histogram in XSANE (GAMA=1.3 B=120 C=120 for example)
</EM><BR>
<EM>&gt; This causes 'holes' in the output histogram (the dark values go 0, 7,
</EM><BR>
<EM>&gt; 11, 15...). So it may be desirable to scan internally with 12
</EM><BR>
<EM>&gt; bits/color, even if the output is only 8 bits - to provide 'meat' for
</EM><BR>
<EM>&gt; histogram stretching.
</EM><BR>
<P>Hi Marko,
<BR>
<P>the preview is always done with 8/24bpp.
<BR>
If you select &quot;use custom gamma table&quot; the real scan is done with full
<BR>
bit depth (12/36 bpp for the Astra 1220S) and the gamma correction
<BR>
is done with a transformation from 36-&gt;24bpp in the scanner.
<BR>
<P><P><EM>&gt; Increasing the exposure time would help here (in the dark areas) but
</EM><BR>
<EM>&gt; would probably cause overflow in the bright pixels.
</EM><BR>
The Astra 1220S does not support change of the exposure time.
<BR>
<P>&nbsp;&nbsp;
<BR>
<EM>&gt; 1. at each scanhead position take several readings and average them
</EM><BR>
<EM>&gt; before moving the scanhead on.
</EM><BR>
This can not be done in the sane backend because the scanner controls
<BR>
the movement of the scanhead.
<BR>
<P><EM>&gt;
</EM><BR>
<EM>&gt; 2. run several full scans (running the scanhead back and forth across
</EM><BR>
<EM>&gt; the scan area). (smpling only when moving forward)
</EM><BR>
This would not be a backend function, this should be done in a frontend.
<BR>
<P>I will add it as &quot;may be one day&quot; to the end of the todo list of xsane.
<BR>
But I am not sure if it will ever come.
<BR>
<P>But a suggestion:
<BR>
<P>xsane is able to auto-increase the file name counter.
<BR>
<P>Scan an image n times as image-01.pnm to image-nn.pnm
<BR>
<P>Write a tool that reads image-01.pnm to image-nn.pnm
<BR>
and does average and save it to image.pnm
<BR>
<P>Bye
<BR>
Oliver
<BR>
<P><PRE>
--
Homepage: <A HREF="http://www.wolfsburg.de/~rauch">http://www.wolfsburg.de/~rauch</A>
sane-umax: <A HREF="http://www.wolfsburg.de/~rauch/sane/sane-umax.html">http://www.wolfsburg.de/~rauch/sane/sane-umax.html</A>
xsane: <A HREF="http://www.wolfsburg.de/~rauch/sane/sane-xsane.html">http://www.wolfsburg.de/~rauch/sane/sane-xsane.html</A>
E-Mail: mailto:<A HREF="mailto:Oliver.Rauch@Wolfsburg.DE?Subject=Re:%20UMAX%20transparency%20adapter%20/%20averaging&In-Reply-To=&lt;3A33A2AA.79F88581@wolfsburg.de&gt;">Oliver.Rauch@Wolfsburg.DE</A>
<P>--
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