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98 wiersze
4.6 KiB
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<!-- received="Sun Jun 21 05:04:57 1998 PDT" -->
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<!-- sent="Sun, 21 Jun 1998 12:13:54 +0200 (MET DST)" -->
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<!-- name="becka@rz.uni-duesseldorf.de" -->
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<!-- email="becka@rz.uni-duesseldorf.de" -->
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<!-- subject="Re: UMax 1220S" -->
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<!-- id="m0ynh8F-0000XLC@charon.beck-sw.de" -->
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<!-- inreplyto="199806201845.LAA32094@saul9.u.washington.edu" -->
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<title>sane-devel: Re: UMax 1220S</title>
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<h1>Re: UMax 1220S</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>Sun, 21 Jun 1998 12:13:54 +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#176">[ date ]</a><a href="index.html#176">[ thread ]</a><a href="subject.html#176">[ subject ]</a><a href="author.html#176">[ author ]</a>
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<li> <b>Next message:</b> <a href="0177.html">Gunnar Weikamp: "Mustek Scanner 12000SP gives wrong SCSI-Information"</a>
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<li> <b>Previous message:</b> <a href="0175.html">Antal Novak: "backend development"</a>
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<li> <b>In reply to:</b> <a href="0173.html">Zach Fine: "Re: UMax 1220S"</a>
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<!-- nextthread="start" -->
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<li> <b>Next in thread:</b> <a href="0174.html">Nicolas Lucas de Peslouan: "Re: UMax 1220S"</a>
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</ul>
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Hi !<br>
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<p>
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<i>> Jim> Why does my scanner provide resolutions up to 9600 dpi when</i><br>
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<i>> Jim> the default resolution for photos seems to be 100 and OCR</i><br>
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<i>> Jim> 300? What use is 9600 - scanning postage stamps?</i><br>
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<p>
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*grin* Marketing.<br>
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<p>
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<i>> FWIW, most consumer level scanners on the market scan with a maximum</i><br>
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<i>> optical resolution of 300-600dpi. Many scanners are marketed with</i><br>
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<i>> such claims as "scans at up to 9600dpi (interpolated)". This is a</i><br>
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<i>> joke, false advertising, and ought to be illegal. </i><br>
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<p>
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Yep. The problem probably is, that most law-folks do not understand<br>
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the technical details ...<br>
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<br>
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<i>> Interpolation is a process of creating a new pixel based on the pixels</i><br>
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<i>> surrounding it. Interpolation can look ok at low levels, but it is</i><br>
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<i>> not adding any real, captured information to your scanned image. I'm</i><br>
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<i>> always surprised that the marketing folk stop at 9600dpi, they might</i><br>
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<i>> as well advertise "scans at 1billion dpi (interpolated)", since</i><br>
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<i>> besides disk and memory space, there's no limit to how many</i><br>
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<i>> interpolated pixels can be added to a scan.</i><br>
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<p>
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Well - maybe someone with a clue about physics might jump in, then.<br>
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<p>
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There is actually a hard limit on achievable _real_ (not interpolated)<br>
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resolution. Except for some paranoid exceptions (SNOM for those that<br>
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are interested), any optical system is limited by diffraction.<br>
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<p>
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That means, that you cannot resolve structures below the wavelength<br>
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of the light you are using to look at it.<br>
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<p>
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Visible light ranges at around 400-700nm. Let's have a look at the<br>
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red component (longest wavelength) and assume we look at a bright red<br>
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at 620nm.<br>
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<p>
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Now there is a simple calculation:<br>
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<p>
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MaxDPI = 1 Inch / MinimumDotSize <br>
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<p>
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MaxDPI = 25.4 mm / 620nm = 25.4e-3 / 620e-9 = 25.4/620 * 1e+6 = 40968.<br>
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<p>
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That means the marketing folks have only two numbers left, if they don't <br>
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want to advertise beyond physical limits of real achieveable resolution :<br>
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19200 and 38400 (assuming they keep going up in *2 increments).<br>
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<p>
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So I assume the 9600 is chosen, because it has the nice "9" as the<br>
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first digit (you know - something beginning with a 9 must be pretty <br>
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high ... :-).<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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======== GGI - The Right Thing To Do : <a href="http://www.ggi-project.org/">http://www.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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<!-- 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="0177.html">Gunnar Weikamp: "Mustek Scanner 12000SP gives wrong SCSI-Information"</a>
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<li> <b>Previous message:</b> <a href="0175.html">Antal Novak: "backend development"</a>
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<li> <b>In reply to:</b> <a href="0173.html">Zach Fine: "Re: UMax 1220S"</a>
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<!-- nextthread="start" -->
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<li> <b>Next in thread:</b> <a href="0174.html">Nicolas Lucas de Peslouan: "Re: UMax 1220S"</a>
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<!-- reply="end" -->
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</ul>
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