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3.8 KiB
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<!-- received="Wed Jun 18 15:52:50 1997 MST" -->
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<!-- sent="Wed, 18 Jun 1997 15:46:19 -0700" -->
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<!-- name="David Mosberger-Tang" -->
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<!-- email="davidm@azstarnet.com" -->
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<!-- subject="Re: QuickCam bit depth wired to 8: why?" -->
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<!-- id="199706182246.PAA21642@panda.mosberger" -->
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<!-- inreplyto="199706182212.SAA02540@lemur.magnet.com" -->
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<title>sane-devel: Re: QuickCam bit depth wired to 8: why?</title>
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<h1>Re: QuickCam bit depth wired to 8: why?</h1>
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<b>David Mosberger-Tang</b> (<a href="mailto:davidm@azstarnet.com"><i>davidm@azstarnet.com</i></a>)<br>
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<i>Wed, 18 Jun 1997 15:46:19 -0700</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#116">[ date ]</a><a href="index.html#116">[ thread ]</a><a href="subject.html#116">[ subject ]</a><a href="author.html#116">[ author ]</a>
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<li> <b>Next message:</b> <a href="0117.html">Andrew Kuchling: "Re: QuickCam bit depth wired to 8: why?"</a>
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<li> <b>Previous message:</b> <a href="0115.html">Andrew Kuchling: "QuickCam bit depth wired to 8: why?"</a>
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<li> <b>In reply to:</b> <a href="0115.html">Andrew Kuchling: "QuickCam bit depth wired to 8: why?"</a>
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<!-- nextthread="start" -->
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<li> <b>Next in thread:</b> <a href="0117.html">Andrew Kuchling: "Re: QuickCam bit depth wired to 8: why?"</a>
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<li> <b>Reply:</b> <a href="0117.html">Andrew Kuchling: "Re: QuickCam bit depth wired to 8: why?"</a>
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<!-- reply="end" -->
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</ul>
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<!-- body="start" -->
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<i>>>>>> On Wed, 18 Jun 1997 18:12:08 -0400 (EDT), Andrew Kuchling <<a href="mailto:amk@magnet.com">amk@magnet.com</a>> said:</i><br>
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<p>
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Andrew> I was wondering why scanimage was producing such dark<br>
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Andrew> images, and realized that the bit depth returned from<br>
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Andrew> sane_get_parameters() in qcam.c is hard-wired to 8--the<br>
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Andrew> configured bit depth (4 or 6 bits) isn't used. Why is that<br>
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Andrew> done?<br>
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<p>
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4 and 6 bit/sample are unsupported depths (see below).<br>
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<p>
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Andrew> scanimage.c also assumes that grey-scale images will always<br>
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Andrew> have a bit depth of 8; for the moment I've been simply<br>
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Andrew> hand-editing the generated .pnm file, changing the number of<br>
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Andrew> colours from 255 to 63.<br>
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<p>
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Argh, I think I mentioned in the SANE docs that the bit depth must be<br>
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either 1, 8 or 16 bits per sample, but I just checked and found that I<br>
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didn't say so explicitly. I fixed that now by adding the following to<br>
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the section on the Image Data Format:<br>
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<p>
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\begin{changebar}<br>
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Valid bit depths are 1, 8, or 16 bits per sample. If a device's<br>
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natural bit depth is something else, it is up to the driver to scale<br>
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the sample values appropriately (e.g., a 4 bit sample could be<br>
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scaled by a factor of four to represent a sample value of depth 8).<br>
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\end{changebar}<br>
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<p>
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So, the intent is that the qcam backend scales 4 and 6 bit samples to<br>
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8 bit samples. Then everything will work as intended.<br>
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<p>
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--david<br>
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<p>
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<pre>
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--
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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="0117.html">Andrew Kuchling: "Re: QuickCam bit depth wired to 8: why?"</a>
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<li> <b>Previous message:</b> <a href="0115.html">Andrew Kuchling: "QuickCam bit depth wired to 8: why?"</a>
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<li> <b>In reply to:</b> <a href="0115.html">Andrew Kuchling: "QuickCam bit depth wired to 8: why?"</a>
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<!-- nextthread="start" -->
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<li> <b>Next in thread:</b> <a href="0117.html">Andrew Kuchling: "Re: QuickCam bit depth wired to 8: why?"</a>
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<li> <b>Reply:</b> <a href="0117.html">Andrew Kuchling: "Re: QuickCam bit depth wired to 8: why?"</a>
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<!-- reply="end" -->
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</ul>
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