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<!-- received="Fri Jul 30 18:04:46 1999 PDT" -->
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<!-- name="Stephen Williams" -->
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<!-- subject="Re: SANE & exposure times" -->
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<title>sane-devel: Re: SANE & exposure times</title>
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<h1>Re: SANE & exposure times</h1>
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<b>Stephen Williams</b> (<a href="mailto:steve@icarus.com"><i>steve@icarus.com</i></a>)<br>
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<i>Fri, 30 Jul 1999 18:03:20 -0700</i>
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<p>
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<li> <b>Messages sorted by:</b> <a href="date.html#222">[ date ]</a><a href="index.html#222">[ thread ]</a><a href="subject.html#222">[ subject ]</a><a href="author.html#222">[ author ]</a>
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<li> <b>Next message:</b> <a href="0223.html">Ewald R. de Wit: "Re: SANE & exposure times"</a>
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<li> <b>Previous message:</b> <a href="0221.html">Andreas Rick: "Re: SANE & exposure times"</a>
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<li> <b>In reply to:</b> <a href="0221.html">Andreas Rick: "Re: SANE & exposure times"</a>
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<li> <b>Next in thread:</b> <a href="0224.html">Ewald R. de Wit: "Re: SANE & exposure times"</a>
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<li> <b>Next in thread:</b> <a href="0223.html">Ewald R. de Wit: "Re: SANE & exposure times"</a>
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<li> <b>Reply:</b> <a href="0224.html">Ewald R. de Wit: "Re: SANE & exposure times"</a>
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<a href="mailto:rickand@gemse.fr">rickand@gemse.fr</a> said:<br>
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<i>> When scanning color images, optical density allone is not enough, we</i><br>
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<i>> need to know what color (wavelength) was used to do the scanning and</i><br>
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<i>> what is the detector efficiency as a function of wavelength.</i><br>
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<p>
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Not so simple. A red sensor, for example, is not just sensitive to a<br>
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single color that it defines as red. Instead it is typically sensitive<br>
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to colors ranging from ultraviolet to infrared. And if that were not<br>
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enough, the source of light has its own spectrum as well.<br>
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<p>
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A red signal is generated when the frequencies that the sensor respond<br>
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to, the frequencies that the illuminator emit, and the frequencies that<br>
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subject reflect (or transmit, for transparencies) all match. It gets even<br>
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more complicated in some scanners, that have color filters in the optical<br>
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path. These are sometimes used to compensate for issues wrt illumination<br>
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or CCD sensitivity.<br>
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<p>
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The closest thing there is to a calibration table for scanners is<br>
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an ICC color profile.<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">steve@icarus.com</a> But I have promises to keep,
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<a href="mailto:steve@picturel.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>
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<p>
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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="0223.html">Ewald R. de Wit: "Re: SANE & exposure times"</a>
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<li> <b>Previous message:</b> <a href="0221.html">Andreas Rick: "Re: SANE & exposure times"</a>
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<li> <b>In reply to:</b> <a href="0221.html">Andreas Rick: "Re: SANE & exposure times"</a>
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<!-- nextthread="start" -->
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<li> <b>Next in thread:</b> <a href="0224.html">Ewald R. de Wit: "Re: SANE & exposure times"</a>
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<li> <b>Next in thread:</b> <a href="0223.html">Ewald R. de Wit: "Re: SANE & exposure times"</a>
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<li> <b>Reply:</b> <a href="0224.html">Ewald R. de Wit: "Re: SANE & exposure times"</a>
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</ul>
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