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<!-- received="Fri Apr 23 01:16:50 1999 PDT" -->
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<!-- name="becka@rz.uni-duesseldorf.de" -->
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<!-- subject="Re: Scanner internals and SANE backends" -->
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<title>sane-devel: Re: Scanner internals and SANE backends</title>
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<h1>Re: Scanner internals and SANE backends</h1>
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<a href="mailto:becka@rz.uni-duesseldorf.de"><i>becka@rz.uni-duesseldorf.de</i></a><br>
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<i>Fri, 23 Apr 1999 10:16:25 +0200 (MET DST)</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#322">[ date ]</a><a href="index.html#322">[ thread ]</a><a href="subject.html#322">[ subject ]</a><a href="author.html#322">[ author ]</a>
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<li> <b>Next message:</b> <a href="0323.html">becka@rz.uni-duesseldorf.de: "Re: Sane config thoughts"</a>
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<li> <b>Previous message:</b> <a href="0321.html">Ole W. Saastad: "Scanning and interpolation"</a>
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Hi <br>
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<p>
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<i>> Can anybody tell me what processing is performed by</i><br>
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<i>> scanners, in general, before sending scanned data to</i><br>
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<i>> a computer. </i><br>
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<p>
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This varies greatly with the scanner. Most don't do much to the data,<br>
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some can interpolate it already inside the scanner (most scanners where<br>
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max x and y resolution are not the same can do so to preset a x=y resolution<br>
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to the user any time). Some scanners have internal image enhancement <br>
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algorithms, especially, if they can make use of the enhanced availability <br>
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of data inside the scanner and reduce the amount of data to be transferred <br>
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over the bus. AFAIK HP has something like that they call "AccuPage" which<br>
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enhances text scans for OCR.<br>
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<p>
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<i>> Also, what does a SANE need backend typically</i><br>
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<i>> do with the scanned data before passing it on to higher</i><br>
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<i>> level software. </i><br>
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<p>
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Not much usually. Pad strange bit depths, unpack strange transfer encodings<br>
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etc.<br>
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<p>
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<i>> In particular what is line-distance correction?</i><br>
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<p>
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That more or less falls into the strange transfer encoding category.<br>
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Scanners often have three different CCD lines for the three basic colors.<br>
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These are some fixed distance apart, which means the red, green and blue <br>
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image are received by the CCD with a fixed offset.<br>
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<p>
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Some scanners buffer the image data internally and correct for it or use<br>
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backtracking for each scan block, while others jusr send the current values<br>
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on the CCD lines, so that the backend needs to "delay" two channels a bit to<br>
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compensate for that offset.<br>
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<p>
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I explained that a few times in the past. Please search the ML archives<br>
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for details.<br>
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<p>
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CU, Andy<br>
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<p>
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<pre>
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--
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Andreas Beck | Email : <<a href="mailto:Andreas.Beck@ggi-project.org">Andreas.Beck@ggi-project.org</a>>
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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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To unsubscribe: echo unsubscribe sane-devel | mail <a href="mailto:majordomo@mostang.com">majordomo@mostang.com</a>
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</pre>
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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="0323.html">becka@rz.uni-duesseldorf.de: "Re: Sane config thoughts"</a>
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<li> <b>Previous message:</b> <a href="0321.html">Ole W. Saastad: "Scanning and interpolation"</a>
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