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<!-- received="Wed May 28 09:40:31 1997 MST" -->
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<!-- sent="Wed, 28 May 1997 09:24:54 -0700" -->
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<!-- name="David Mosberger-Tang" -->
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<!-- email="davidm@azstarnet.com" -->
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<!-- subject="Re: image buffering" -->
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<!-- id="199705281624.JAA07110@panda.mosberger" -->
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<!-- inreplyto="Pine.3.89.9705281733.A7825-0100000@medchem2.pharmazie.uni-halle.de" -->
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<title>sane-devel: Re: image buffering</title>
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<h1>Re: image buffering</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, 28 May 1997 09:24:54 -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#31">[ date ]</a><a href="index.html#31">[ thread ]</a><a href="subject.html#31">[ subject ]</a><a href="author.html#31">[ author ]</a>
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<li> <b>Next message:</b> <a href="0032.html">Gordon Matzigkeit: "Re: image buffering"</a>
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<li> <b>Previous message:</b> <a href="0030.html">David Mosberger-Tang: "Re: HP support"</a>
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<!-- nextthread="start" -->
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<li> <b>Next in thread:</b> <a href="0032.html">Gordon Matzigkeit: "Re: image buffering"</a>
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<li> <b>Reply:</b> <a href="0032.html">Gordon Matzigkeit: "Re: image buffering"</a>
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<!-- reply="end" -->
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</ul>
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<!-- body="start" -->
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Hi Mathias,<br>
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<p>
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<i>>>>>> On Wed, 28 May 1997 17:52:14 +0059 (MDT), "Mathias Weigt (Stud. 94)" <<a href="mailto:p5iba@medchem2.pharmazie.uni-halle.de">p5iba@medchem2.pharmazie.uni-halle.de</a>> said:</i><br>
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<p>
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Mathias> Servus! In the last postings the buffering of images was<br>
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Mathias> mentioned. I thought a little bit and like to know more<br>
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Mathias> about it. In scanimage.c must_buffer is set for handheld<br>
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Mathias> scanners (parm.lines<0) or for three pass scanning (either<br>
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Mathias> of the three frames). I think scanning a full size image<br>
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Mathias> (14 x 8.5 inch) at 600 dpi will cost 125 Mbyte of memory. I<br>
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Mathias> don`t have such an amount of memory (only if I double my<br>
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Mathias> swapspace) and I think not many people on Linux have.<br>
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Mathias> David mentioned that a temporary file wouldn`t be a nice<br>
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Mathias> solution. Here is my question: Why not ? Shouldn't it be<br>
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Mathias> possible to write three temporary files for the red, green<br>
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Mathias> and blue frame (of course not as image but the red bytes in<br>
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Mathias> a line...) so that each will consume 1/3 of the entire<br>
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Mathias> image in space? After the last pass the picture can be put<br>
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Mathias> together from those three files and send to stdout or file.<br>
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<p>
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It's certainly possible. Michael suggested using mmap'ing to provide<br>
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backing store in the filesystem instead of the swap-space. Of the two<br>
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solutions, I think mmap is technically preferable when there is plenty<br>
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memory available. On the other hand, mmap is still quite a portability<br>
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nightmare, so using regular files might still be better, overall.<br>
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<p>
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However, the real issue is: what if you have tons of memory/swap-space<br>
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but not much free diskspace? Don't say that doesn't happen. My<br>
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system has 64MB of RAM and much more swap-space, yet I'm hard-pressed<br>
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to find 256MB of free space on any of the filesystems... So, in that<br>
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case, using temporary files would prevent me from acquiring the images<br>
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(since you'd need 128MB of temporary space plus 128MB to store the<br>
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resulting image).<br>
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<p>
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To me, it seems like we should use memory/swap-space when it looks<br>
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like the image might fit in the available memory/swap-space and use<br>
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temporary files otherwise. E.g., on Linux, we could base this<br>
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decision on MemTotal: as reported in /proc/meminfo.<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="0032.html">Gordon Matzigkeit: "Re: image buffering"</a>
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<li> <b>Previous message:</b> <a href="0030.html">David Mosberger-Tang: "Re: HP support"</a>
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<!-- nextthread="start" -->
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<li> <b>Next in thread:</b> <a href="0032.html">Gordon Matzigkeit: "Re: image buffering"</a>
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<li> <b>Reply:</b> <a href="0032.html">Gordon Matzigkeit: "Re: image buffering"</a>
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<!-- reply="end" -->
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</ul>
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