sane-project-website/old-archive/1999-08/0156.html

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<title>sane-devel: Re: Starting a discussion about SANE and TWAIN...</title>
<h1>Re: Starting a discussion about SANE and TWAIN...</h1>
<b>Nick Lamb</b> (<a href="mailto:njl98r@ecs.soton.ac.uk"><i>njl98r@ecs.soton.ac.uk</i></a>)<br>
<i>Sun, 15 Aug 1999 03:49:16 +0100 (GMT)</i>
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On Sat, 14 Aug 1999, Stephen Williams wrote:<br>
<p>
<i>&gt; So all I'm looking for at the moment is some sort of means to negotiate</i><br>
<i>&gt; frame formats.</i><br>
<p>
Ok. IIRC Your scanners can do RGB, but prefer not to for speed reasons?<br>
So in writing the backend, first start by supporting this (slow) option<br>
as the default and then add an option (eventually to be a well-known<br>
option in SANE 2.0) which controls the compression.<br>
<p>
I haven't finished looking at this, but so far I think this will work<br>
for SANE_FRAME_JFIF (perhaps code 6 in the enumeration)<br>
<p>
OPTION ONE -- If the backend knows before sending any data how much<br>
there will be exactly in the JFIF image.<br>
<p>
format = SANE_FRAME_JFIF (6)<br>
last_frame = TRUE<br>
lines = 1<br>
depth = 8<br>
pixels_per_line = 0<br>
bytes_per_line = sizeof(JFIF image)<br>
<p>
OPTION TWO -- If the backend doesn't know how much data there is until<br>
later, or until it runs out.<br>
<p>
format = SANE_FRAME_JFIF (6)<br>
last_frame = TRUE<br>
lines = -1<br>
depth = 8<br>
pixels_per_line = 0<br>
bytes_per_line = 4096 (or 65536, whatever)<br>
<p>
A compliant SANE 1.0 frontend will reject such frames without danger, a<br>
proposed 2.0 frontend without any JFIF code will save them to a file<br>
and likely use a buffer with size ~= bytes_per_line.<br>
An intelligent SANE 2.0 frontend will know to sane_read(...) until EOF<br>
and then deal with the JFIF data appropriately.<br>
<p>
OPTION TWO is probably the one to go for, but I like OPTION ONE at lot<br>
because it's so very simple ;)<br>
<p>
Might try to write a modifed scanimage which handles all this tomorrow<br>
if I get a chance. Now, time for bed.<br>
<p>
Nick.<br>
<p>
<p>
<pre>
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<li> <b>Next message:</b> <a href="0157.html">Stephen Williams: "Re: Starting a discussion about SANE and TWAIN..."</a>
<li> <b>Previous message:</b> <a href="0155.html">Nick Lamb: "Re: SANE V2"</a>
<li> <b>In reply to:</b> <a href="0154.html">Stephen Williams: "Re: Starting a discussion about SANE and TWAIN..."</a>
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