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<!-- received="Thu Dec 3 08:08:41 1998 PST" -->
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<!-- sent="02 Dec 1998 11:36:36 -0800" -->
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<!-- name="David Fox" -->
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<!-- email="dsfox@cogsci.ucsd.edu" -->
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<!-- subject="Re: Adjusting contrast and brightness" -->
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<!-- id="´ßkUU" -->
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<!-- inreplyto="Wed, 2 Dec 1998 10:26:09 -0500 (EST)"" -->
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<title>sane-devel: Re: Adjusting contrast and brightness</title>
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<h1>Re: Adjusting contrast and brightness</h1>
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<b>David Fox</b> (<a href="mailto:dsfox@cogsci.ucsd.edu"><i>dsfox@cogsci.ucsd.edu</i></a>)<br>
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<i>02 Dec 1998 11:36:36 -0800</i>
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<p>
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<ul>
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<li> <b>Messages sorted by:</b> <a href="date.html#22">[ date ]</a><a href="index.html#22">[ thread ]</a><a href="subject.html#22">[ subject ]</a><a href="author.html#22">[ author ]</a>
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<li> <b>Next message:</b> <a href="0023.html">William L. Sebok: "Re: Adjusting contrast and brightness"</a>
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<li> <b>Previous message:</b> <a href="0021.html">Matto Marjanovic: "Patch 1 for microtek backend v0.10"</a>
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<li> <b>In reply to:</b> <a href="0010.html">William L. Sebok: "Re: Adjusting contrast and brightness"</a>
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<!-- nextthread="start" -->
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<li> <b>Next in thread:</b> <a href="0018.html">Oliver Rauch: "Re: Adjusting contrast and brightness"</a>
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</ul>
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<!-- body="start" -->
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"William L. Sebok" <<a href="mailto:wls@astro.umd.edu">wls@astro.umd.edu</a>> writes:<br>
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<p>
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<i>> David Fox says:</i><br>
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<i>></i><br>
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<i>> > What I miss from the Windows scanning software is the way it could</i><br>
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<i>> > automatically choose good settings for the brightness and contrast</i><br>
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<i>> > based on the selected section of the preview. I'm interested in</i><br>
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<i>> > implementing this for xscanimage, can anyone point me to a good</i><br>
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<i>> > algorithm for doing this, or to a source of good algorithms?</i><br>
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<i>></i><br>
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<i>> Actually, automatically choosing brightness, contrast and gamma from</i><br>
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<i>> a selection on the preview is exactly the feature on the windows</i><br>
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<i>> driver for my Umax S12 that I miss most in sane. That and being</i><br>
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<i>> able to zoom the preview window to make a decently precise</i><br>
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<i>> selection.</i><br>
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<p>
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Well, then I suppose we can begin to make a few conjectures. One<br>
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approach would be to interactively modify the appearance of the<br>
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preview image based on the current settings of the controls. This<br>
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could be done based on a calibration run performed on a test image<br>
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which would record the behavior of the scanner at various settings.<br>
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My preliminary tests show that my HP 3c scanner exhibits a fairly<br>
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linear response to these controls. Perhaps it could be built into the<br>
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back end. A larger and/or adjustable preview area will be an<br>
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essential prerequisite to making this useful.<br>
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<p>
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A real-time display of the brightness histogram of the preview image<br>
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might be a useful stopgap measure.<br>
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<p>
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Having the software actually select the contrast and brightness and<br>
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gamma is a lot trickier, with subjective elements. Its one of those<br>
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problems, like the travelling salesman problem, that are impossible in<br>
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theory but solved in practice every day. Are the algorithms for doing<br>
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this proprietary, or are there no image processing experts here? I<br>
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know about image synthesis, but not much about image processing.<br>
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<p>
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My slide scanner also does color cast removal under Windows. I<br>
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believe this is done by actually examining the color of the emulsion<br>
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by adjusting the focus. Its not working under Sane yet so I can't<br>
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investigate this right now.<br>
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<pre>
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--
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David Fox <a href="http://hci.ucsd.edu/dsf">http://hci.ucsd.edu/dsf</a> xoF divaD
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UCSD HCI Lab baL ICH DSCU
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<p>
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<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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</pre>
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<!-- body="end" -->
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<p>
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<ul>
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<!-- next="start" -->
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<li> <b>Next message:</b> <a href="0023.html">William L. Sebok: "Re: Adjusting contrast and brightness"</a>
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<li> <b>Previous message:</b> <a href="0021.html">Matto Marjanovic: "Patch 1 for microtek backend v0.10"</a>
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<li> <b>In reply to:</b> <a href="0010.html">William L. Sebok: "Re: Adjusting contrast and brightness"</a>
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<!-- nextthread="start" -->
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<li> <b>Next in thread:</b> <a href="0018.html">Oliver Rauch: "Re: Adjusting contrast and brightness"</a>
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<!-- reply="end" -->
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</ul>
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