sane-project-website/old-archive/1999-04/0057.html

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<title>sane-devel: Re: 16 bit per sample support</title>
<h1>Re: 16 bit per sample support</h1>
<b>Nick Lamb</b> (<a href="mailto:njl98r@ecs.soton.ac.uk"><i>njl98r@ecs.soton.ac.uk</i></a>)<br>
<i>Sun, 4 Apr 1999 14:54:35 +0100 (BST)</i>
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On Sun, 4 Apr 1999, Jonathan A. Buzzard wrote:<br>
<p>
<i>&gt; </i><br>
<i>&gt; <a href="mailto:David.Mosberger@acm.org">David.Mosberger@acm.org</a> said:</i><br>
<i>&gt; &gt; This is perfectly well defined in section 3.2:</i><br>
<i>&gt; &gt;   ... Valid bit depths are 1, 8, or 16 bits per sample.</i><br>
<i>&gt; &gt;   If a device's natural bit depth is something else, it is up</i><br>
<i>&gt; &gt;   to the driver to scale the sample values appropriately (e.g.,</i><br>
<i>&gt; &gt;   a 4 bit sample could be scaled by a factor of four to represent</i><br>
<i>&gt; &gt;   a sample value of depth 8). </i><br>
<i>&gt; </i><br>
<i>&gt; Possibly depending on the device this should be configurable. If I</i><br>
<i>&gt; was scanning an X-ray at say 12bits I would be very upset if the backend</i><br>
<i>&gt; then stretched it to 16bits.</i><br>
<p>
I'm not sure why. The only (small) disadvantage is that there is an increase<br>
in bandwidth from the backend to the frontend. For most users, especially<br>
those looking for maximum performance, this is CPU bandwidth, and thus<br>
very expendable. <br>
<p>
There is no data loss (watch this...<br>
 0xabc (12bit) --&gt; 0xabca (16bit) --&gt; 0xabc (12bit)<br>
 0x123 (12bit) --&gt; 0x1231 (16bit) --&gt; 0x123 (12bit)<br>
<p>
All the file formats you're likely to use are either 8-bit (and will lose<br>
the bottom four bits however they're encoded) or 16-bit (and will stretch<br>
anything smaller just as the backend does to fit internal structures).<br>
<p>
If you're scanning X rays over a low-bandwidth (say 10Mbit) network and<br>
it sucks to have a 33% longer download time, then run the connection over<br>
a compressed virtual pipe using ssh :)<br>
<p>
Nick.<br>
<p>
<p>
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<li> <b>In reply to:</b> <a href="0053.html">Jonathan A. Buzzard: "Re: 16 bit per sample support"</a>
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