sane-project-website/old-archive/1999-07/0092.html

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<!-- name="Oliver Rauch" -->
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<!-- subject="Re: Xsane questions and wish list" -->
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<title>sane-devel: Re: Xsane questions and wish list</title>
<h1>Re: Xsane questions and wish list</h1>
<b>Oliver Rauch</b> (<a href="mailto:oliver.rauch@Wolfsburg.DE"><i>oliver.rauch@Wolfsburg.DE</i></a>)<br>
<i>Fri, 16 Jul 1999 15:44:56 +0200</i>
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Steve Gunnell wrote:<br>
<p>
<i>&gt; Oliver Rauch wrote:</i><br>
<i>&gt;</i><br>
<i>&gt; &gt; xsane uses the gamma bit depth the backend uses,</i><br>
<i>&gt; &gt; but the scanner gamma table has to be activated (normally</i><br>
<i>&gt; &gt; by custom gamma table in standard options, but backend dependent)!</i><br>
<i>&gt;</i><br>
<i>&gt; I'm just using the default settings. I assumed the scanner was beingchanged</i><br>
<i>&gt; because when I closed xsane and went back to xscanimage</i><br>
<i>&gt; my attempts to correct the white level in xsane were still being applied</i><br>
<i>&gt; to the xscanimage previews. I had to turn the scanner off to clear them.</i><br>
<i>&gt;</i><br>
<p>
That sould not happen, may be there is a bug in the backend!<br>
<p>
<i>&gt; &gt; For what do you need the values? In the histogram window</i><br>
<i>&gt;</i><br>
<i>&gt; &gt; you have the silders and the color density is given in the</i><br>
<i>&gt; &gt; histogram window.</i><br>
<i>&gt;</i><br>
<i>&gt; I'm scanning negatives. So I need to remove the colour mask from the</i><br>
<i>&gt; images.To do that I need to set the white point to the value of the colour</i><br>
<i>&gt; mask. So what</i><br>
<i>&gt; I do is select a scanned chunk of colour mask and average it using the gimp</i><br>
<i>&gt; generic convolution tool to give me the average RGB value for the colour</i><br>
<i>&gt; mask.</i><br>
<i>&gt; If I had a editable value box I could enter these values as the white point</i><br>
<i>&gt; just like</i><br>
<i>&gt; I do with the gimp histogram tool rather than having to mess around with</i><br>
<i>&gt; little</i><br>
<i>&gt; sliders that I can't control accurately. If I could set the colour mask</i><br>
<i>&gt; scaling and</i><br>
<i>&gt; the negative colour inversion once per film in xsane then I can save two</i><br>
<i>&gt; gimp</i><br>
<i>&gt; operations per frame which would be a considerable saving over the 45</i><br>
<i>&gt; minutes per strip of 4 negatives that the process takes now.</i><br>
<i>&gt;</i><br>
<i>&gt; &gt; If you want to use values take the brightness, contrast and gamma</i><br>
<i>&gt; &gt; values!</i><br>
<i>&gt;</i><br>
<i>&gt; These are no use to me because they are arbitrary values that do not</i><br>
<i>&gt; simplyrelate to the RGB values that I need to change.</i><br>
<i>&gt;</i><br>
<p>
The highlitght and shadow values are also not the same, they depend on the<br>
bit depth (8bit =256, 10 bit=1024 and so on).<br>
<p>
The contrast and brightness are well defined:<br>
-100% brightness moves all values in 8 bit by -128<br>
-100% contrast makes all colors to one value,<br>
+100% contrast doubles the range of used values<br>
<p>
Xsane and the gimp should use the same contrast, brightness and gamma values<br>
for the same conversion!<br>
<p>
<p>
<i>&gt;</i><br>
<i>&gt; If you have a better method for processing negatives that takes advantage of</i><br>
<i>&gt;</i><br>
<i>&gt; xsane's features then I would love to know about it.</i><br>
<i>&gt;</i><br>
<p>
I disable rgb default, activate negative option and do a preview scan,<br>
then I disable all but one color in the histogram window and set the<br>
highlight and shadow sliders to the used range, this is done for<br>
red, green and blue. Then I set all gamma values to 1.0<br>
<p>
Write down the 4 values for brightness and contrast, they are a good<br>
start for the film (agfa, fuji,...)<br>
<p>
In future it is planned to save different settings, then you can save a<br>
correction for Agfa negatives, one for Fuji and so on.<br>
<p>
To get real good results, you afterwards have to do a calibration by<br>
hand, but that is the same as scanning positives!<br>
<p>
Bye<br>
Oliver<br>
<p>
<pre>
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EMAIL: <a href="mailto:Oliver.Rauch@Wolfsburg.DE">Oliver.Rauch@Wolfsburg.DE</a>
WWW: <a href="http://www.wolfsburg.de/~rauch">http://www.wolfsburg.de/~rauch</a>
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<ul>
<!-- next="start" -->
<li> <b>Next message:</b> <a href="0093.html">Lany Wilson: "Leoscan 3S/ Across 3S scanners"</a>
<li> <b>Previous message:</b> <a href="0091.html">Oliver Rauch: "Re: (nil) entry in rcfiles"</a>
<li> <b>Maybe in reply to:</b> <a href="0077.html">Steve Gunnell: "Xsane questions and wish list"</a>
<!-- nextthread="start" -->
<li> <b>Next in thread:</b> <a href="0102.html">Peter Kirchgessner: "Re: Xsane questions and wish list"</a>
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</ul>