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68 wiersze
3.3 KiB
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<!-- received="Fri Jul 30 02:06:55 1999 PDT" -->
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<!-- sent="Fri, 30 Jul 1999 11:24:26 +0200" -->
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<!-- name="Didier Carlier" -->
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<!-- email="Didier.Carlier@sema.be" -->
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<!-- subject="Re: SANE & exposure times" -->
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<!-- id="199907300924.LAA29001@fritz.sema.be" -->
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<!-- inreplyto="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>Didier Carlier</b> (<a href="mailto:Didier.Carlier@sema.be"><i>Didier.Carlier@sema.be</i></a>)<br>
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<i>Fri, 30 Jul 1999 11:24:26 +0200</i>
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<p>
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<li> <b>Messages sorted by:</b> <a href="date.html#220">[ date ]</a><a href="index.html#220">[ thread ]</a><a href="subject.html#220">[ subject ]</a><a href="author.html#220">[ author ]</a>
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<li> <b>Next message:</b> <a href="0221.html">Andreas Rick: "Re: SANE & exposure times"</a>
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<li> <b>Previous message:</b> <a href="0219.html">Stephen Williams: "scanners that do jpeg compression"</a>
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<li> <b>Maybe in reply to:</b> <a href="0208.html">Ewald R. de Wit: "SANE & exposure times"</a>
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<li> <b>Next in thread:</b> <a href="0221.html">Andreas Rick: "Re: SANE & exposure times"</a>
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<a href="mailto:ewald@pobox.com">ewald@pobox.com</a> said:<br>
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<i>> The main use is for scanning negatives. For negatives, density of blue</i><br>
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<i>> is ~3x that of red, and that of green is ~2x that of red (hence the</i><br>
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<i>> orange color of the negative mask). So if you scan with 1:1:1 exposure</i><br>
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<i>> time, the green channel will only use 1/2 of it's full range. In other</i><br>
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<i>> words, you have lost one bit of what is basically your luminance. The</i><br>
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<i>> blue channel is filled for only 1/3 and this poor blue definition can</i><br>
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<i>> also be very visible to the human eye.</i><br>
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<i>></i><br>
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<i>> All this can be solved by scanning with a 1:2:3 exposure so that the</i><br>
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<i>> full range of all channels is utilized. </i><br>
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<p>
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If I look at the RGB values after a scan of a negative, the values of all <br>
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channels go from 0 to 255, so I'm not quite sure of what you are trying to do.<br>
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<p>
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Putting the multiple scan issue aside you can't get more than 8 bits of <br>
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resolution per channel so that you don't loose definition on the blue channel, <br>
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you loose dynamic range.<br>
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I.e. you do not extract the clearer blue details, but you do keep the full 8 bit<br>
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color resolution for the dynamic range that was scanned.<br>
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Am I missing something here ?<br>
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<p>
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Didier<br>
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<p>
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<p>
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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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</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="0221.html">Andreas Rick: "Re: SANE & exposure times"</a>
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<li> <b>Previous message:</b> <a href="0219.html">Stephen Williams: "scanners that do jpeg compression"</a>
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<li> <b>Maybe in reply to:</b> <a href="0208.html">Ewald R. de Wit: "SANE & exposure times"</a>
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<!-- nextthread="start" -->
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<li> <b>Next in thread:</b> <a href="0221.html">Andreas Rick: "Re: SANE & exposure times"</a>
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<!-- reply="end" -->
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</ul>
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