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138 wiersze
7.1 KiB
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<!-- received="Fri Mar 26 00:09:08 1999 PST" -->
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<!-- sent="Fri, 26 Mar 1999 09:03:02 +0100" -->
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<!-- name="Oliver Rauch" -->
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<!-- email="oliver.rauch@Wolfsburg.DE" -->
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<!-- subject="Re: Calibration problem on UMAX Astra 1220S" -->
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<!-- inreplyto="Calibration problem on UMAX Astra 1220S" -->
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<title>sane-devel: Re: Calibration problem on UMAX Astra 1220S</title>
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<h1>Re: Calibration problem on UMAX Astra 1220S</h1>
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<b>Oliver Rauch</b> (<a href="mailto:oliver.rauch@Wolfsburg.DE"><i>oliver.rauch@Wolfsburg.DE</i></a>)<br>
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<i>Fri, 26 Mar 1999 09:03:02 +0100</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#237">[ date ]</a><a href="index.html#237">[ thread ]</a><a href="subject.html#237">[ subject ]</a><a href="author.html#237">[ author ]</a>
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<li> <b>Next message:</b> <a href="0238.html">Luigi Rizzo: "Re: Dexxa / Artec AS6E scanner."</a>
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<li> <b>Previous message:</b> <a href="0236.html">Thomas Scheuermann: "Re: SANE 1.00 + Mustek SE6000SP"</a>
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<li> <b>Maybe in reply to:</b> <a href="0220.html">Dean Martin Townsley: "Calibration problem on UMAX Astra 1220S"</a>
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<!-- nextthread="start" -->
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<li> <b>Next in thread:</b> <a href="0240.html">Oliver Rauch: "Re: Calibration problem on UMAX Astra 1220S"</a>
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<!-- reply="end" -->
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</ul>
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Dean Martin Townsley wrote:<br>
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<p>
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<i>> > What happens or does not happen if you enable quality calibration?</i><br>
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<i>></i><br>
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<i>> Okay I'll let you know the story. I'm trying to scan a card that's basically</i><br>
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<i>> an embossed white graphic on a slightly off-white background. Well, the</i><br>
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<i>> scanner sees that the thing is almost totally white, and saturates the scan</i><br>
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<i>> really bad. The histogram in xsane does not fall off at the high</i><br>
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<i>> Luminosities, it just saturates. From looking at other stuff on the net,</i><br>
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<i>> this appears abnormal, even for stuff on white backgrounds. I am under the</i><br>
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<i>> ipression that this is what the "Quality Calibration" is for (though I could</i><br>
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<i>> be wrong) is to set the white point so that it is not out of the scanner's</i><br>
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<i>> sensing range, as it apparently is on mine since white and off-white come up</i><br>
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<i>> as the same color -- ffffff white. I would assume it's just an impossible</i><br>
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<i>> scan but someone else did it on another scanner and it came out fine, I'm</i><br>
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<i>> just trying to match that (and not even coming close).</i><br>
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<i>> Now for what happens when when I try to use the calibration. Nothing.</i><br>
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<i>> There is no noticable difference in the scans or the activity performed by</i><br>
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<i>> the scanner. I assume that even if the firmware is doing the calibration</i><br>
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<i>> that it still has to DO something i.e. the lamp has to move prior to the</i><br>
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<i>> actual scan. (Again I could be wrong let me know if I am) In my case I find</i><br>
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<i>> no difference between having the button checked or not in the frontend.</i><br>
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<i>></i><br>
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<p>
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No, you are on the wrong way.The quality calibration is not a calibrartion on the<br>
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picuture.<br>
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The ccd line of a scanner does not have the same output values for each pixel.<br>
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So if you would scan a really white area without any calibration, you would<br>
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get values - lets say between 220 and 255.<br>
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To make all these values unique, the scanner scans one line and calculates a<br>
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correction for each ccd pixel. But if you only scan one line you may get a point<br>
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that is not white or the lamp does not have the same power over the caliration time<br>
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so you get errors in your calibration. In quality calibration it is scanned more than<br>
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<p>
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one line and the values of one ccd pixel are avaraged, so the error of the<br>
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calibration<br>
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is smaller.<br>
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<p>
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It has nothing to do with you problem!<br>
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<p>
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What you are looking for is higlight and shadow (or black and white point)<br>
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definition.<br>
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The Astra 1220S only can do this via gamma correction, there are no seperate<br>
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functions<br>
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for this.<br>
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<p>
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If you are scanning in lineart (black/white) mode, open the standard options window<br>
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in<br>
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xsane and move the Threshold slider to the right edge. Then do a preview of your<br>
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image.<br>
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<p>
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If that does not help, you have to do it in grayscale mode.<br>
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Xsane makes available the highlight and shadow function via the hystogram window.<br>
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Open the histogram window, between the two histograms there are some colored blocks.<br>
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In the recent version there are three sliders in the gray block. Move the mid slider<br>
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and<br>
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the left slider to the right, as far as possible. Then do a real scan of the image.<br>
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On a preview<br>
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you will not see any differences, because the preview is always done in 24bpp, the<br>
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real<br>
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scan uses a 36bpp and afterwards converts it to a 24bpp image.<br>
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<p>
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I hope this works for you!<br>
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<p>
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<i>> Hopefully I'm not totally off base here. I think my scanner is capable of</i><br>
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<i>> doing calibration, since the starting of the driver says</i><br>
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<i>> [umax] f/w support function:</i><br>
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<i>> [umax] ---------------------</i><br>
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<i>> [umax] quality calibration</i><br>
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<i>> but it likely performs it in the firmware, since the</i><br>
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<i>> "change" to firmware 1.5 for this scanner was to add software calibration.</i><br>
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<i>></i><br>
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<i>> I think I could do better if I had an idea what I was looking for. What is</i><br>
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<i>> the Quality Calibration supposed to work like? Should it happen at the</i><br>
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<i>> beginning of each scan when the button is checked? Should the scan process</i><br>
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<i>> be different? A two pass scan maybe? If it's not working is this because</i><br>
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<i>> the driver is just not telling the scanner to do it properly? Is this</i><br>
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<i>> documented anywhere or is this a trial and error type thing?</i><br>
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<i>></i><br>
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<p>
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The difference is in the short time before the real scan begins.<br>
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If you don`t see any differences, it is possible that the scanner<br>
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always does a quality calibration independent from the quality bit.<br>
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<p>
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May be you see/hear a difference between a preview scan and a<br>
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real scan.<br>
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<p>
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Bye<br>
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Oliver<br>
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<p>
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<pre>
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--
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EMAIL: <a href="mailto:Oliver.Rauch@Wolfsburg.DE">Oliver.Rauch@Wolfsburg.DE</a>
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WWW: <a href="http://www.wolfsburg.de/~rauch">http://www.wolfsburg.de/~rauch</a>
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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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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="0238.html">Luigi Rizzo: "Re: Dexxa / Artec AS6E scanner."</a>
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<li> <b>Previous message:</b> <a href="0236.html">Thomas Scheuermann: "Re: SANE 1.00 + Mustek SE6000SP"</a>
|
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<li> <b>Maybe in reply to:</b> <a href="0220.html">Dean Martin Townsley: "Calibration problem on UMAX Astra 1220S"</a>
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<!-- nextthread="start" -->
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<li> <b>Next in thread:</b> <a href="0240.html">Oliver Rauch: "Re: Calibration problem on UMAX Astra 1220S"</a>
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<!-- reply="end" -->
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</ul>
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