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<TITLE>sane-devel: Re: Scan ahead</TITLE>
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<META NAME="Author" CONTENT="Tom Martone (tom@martoneconsulting.com)">
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<META NAME="Subject" CONTENT="Re: Scan ahead">
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<H1>Re: Scan ahead</H1>
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<!-- received="Sat Mar 31 08:32:28 2001" -->
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<!-- subject="Re: Scan ahead" -->
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<STRONG>From:</STRONG> Tom Martone (<A HREF="mailto:tom@martoneconsulting.com?Subject=Re:%20Scan%20ahead&In-Reply-To=<3AC60D37.C5A113BD@martoneconsulting.com>"><EM>tom@martoneconsulting.com</EM></A>)<BR>
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<STRONG>Date:</STRONG> Sat Mar 31 2001 - 09:00:39 PST
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<P>
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<!-- next="start" -->
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<LI><STRONG>Next message:</STRONG> <A HREF="0257.html">Henning Meier-Geinitz: "Re: preview and selectable scanarea for MFS-12000's ADF"</A>
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<UL>
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<LI><STRONG>Previous message:</STRONG> <A HREF="0255.html">Karsten Festag: "Re: microtek2 and scsi_read_image_status"</A>
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<LI><STRONG>In reply to:</STRONG> <A HREF="0252.html">Stephen Williams: "Re: Scan ahead"</A>
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<HR NOSHADE><P>
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<P>
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Greetings,
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<BR>
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<P>Stephen Williams wrote:
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<BR>
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<EM>>
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</EM><BR>
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<EM>> <A HREF="mailto:peter@kirchgessner.net?Subject=Re:%20Scan%20ahead&In-Reply-To=<3AC60D37.C5A113BD@martoneconsulting.com>">peter@kirchgessner.net</A> said:
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</EM><BR>
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<EM>> > I dont know a scanner that can store a single frame completely. For an
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</EM><BR>
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<EM>> > A4 scan at 600 dpi with 24bit you would need about 100MB of memory.
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</EM><BR>
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<EM>>
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</EM><BR>
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<EM>> I know several, and they are grayscale and color. And we keep building
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</EM><BR>
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<EM>> more because this pipelining really does help when you are talking about
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</EM><BR>
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<EM>> large batches. Of course, we are not talking about desk-top flat-bed
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</EM><BR>
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<EM>> scanners here:-)
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</EM><BR>
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<P>The Bell+Howell CopiScan series scanners have an Remote SCSI Controller
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<BR>
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that is a little computer with memory sufficient to store images
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<BR>
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and perform operations such as compression, automatic border detection,
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<BR>
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deskew, etc. This is done in b/w at resolutions ~200dpi-400dpi.
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<BR>
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Depending on the size of the pages, there can be room for several
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<BR>
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images in the cache. As the image data is read by the host computer
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<BR>
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the cache is freed and more pages are fed through.
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<BR>
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<P><EM>> So Marius asked a valid question and I'm curious myself how this issue
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</EM><BR>
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<EM>> was dealt with by others. I suspect the answer is going to be something
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</EM><BR>
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<EM>> like "a child process does the pipelining."
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</EM><BR>
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<P>The Bell + Howell has a batch-scanning mode which is used to implement
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<BR>
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the scan-ahead functionality. Once started, the scanner keeps scanning
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<BR>
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as fast as it can (based on the RSC cache availability, etc) until the
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<BR>
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feeder is out of documents, the stop button on the scanner is pressed
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<BR>
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or the host aborts/cancels batch mode.
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<BR>
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<P>The normal non-batch mode would wait for the host to send the start
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<BR>
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scan command, and this would never result in the full rated throughput.
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<BR>
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<P>On the SANE side, the sequence of calls to scan a feeder full of
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<BR>
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documents will look like this (... indicates multiple calls):
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<P>[bh] sane_init called
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<BR>
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[bh] sane_open called
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<BR>
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[bh] sane_control_option called (option:0, action:0)...
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<BR>
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[bh] sane_get_option_descriptor called (option:0)...
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<BR>
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[bh] sane_start called
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<BR>
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[bh] sane_get_parameters called
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<BR>
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[bh] sane_read called...
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<BR>
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[bh] sane_start called
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<BR>
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[bh] sane_get_parameters called
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<BR>
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[bh] sane_read called...
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<BR>
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[bh] sane_start called
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<BR>
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[bh] sane_get_parameters called
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<BR>
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[bh] sane_read called...
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<BR>
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[bh] sane_start called
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<BR>
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[bh] sane_get_parameters called
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<BR>
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[bh] sane_read called...
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<BR>
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[bh] sane_start called
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<BR>
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[bh] sane_get_parameters called
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<BR>
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[bh] sane_read called...
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<BR>
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[bh] sane_start called
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<BR>
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[bh] sane_get_parameters called
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<BR>
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[bh] sane_read called...
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<BR>
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[bh] sane_start called (returns SANE_STATUS_NO_DOCS)
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<BR>
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[bh] sane_cancel called
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<BR>
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[bh] sane_close called
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<BR>
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[bh] sane_exit called
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<BR>
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<P>It is important NOT to call sane_cancel until the entire batch is
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<BR>
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finished (sane_start returns SANE_STATUS_NO_DOCS). This gives the
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<BR>
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backend the understanding of the front-end's notion of "the batch".
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<BR>
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<P>In the bh driver, I've not implemented the non-blocking io mode nor
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<BR>
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do I use a child process for buffering. The performance exhibited
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<BR>
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is close to the rated speed and the scanner seems to be swallowing
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<BR>
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pages as fast as it physically can.
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<BR>
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<P>Tom Martone
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<BR>
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<P><PRE>
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--
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Source code, list archive, and docs: <A HREF="http://www.mostang.com/sane/">http://www.mostang.com/sane/</A>
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To unsubscribe: echo unsubscribe sane-devel | mail <A HREF="mailto:majordomo@mostang.com?Subject=Re:%20Scan%20ahead&In-Reply-To=<3AC60D37.C5A113BD@martoneconsulting.com>">majordomo@mostang.com</A>
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</PRE>
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<LI><STRONG>Next message:</STRONG> <A HREF="0257.html">Henning Meier-Geinitz: "Re: preview and selectable scanarea for MFS-12000's ADF"</A>
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<LI><STRONG>Previous message:</STRONG> <A HREF="0255.html">Karsten Festag: "Re: microtek2 and scsi_read_image_status"</A>
|
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<LI><STRONG>In reply to:</STRONG> <A HREF="0252.html">Stephen Williams: "Re: Scan ahead"</A>
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<SMALL>
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<EM>
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This archive was generated by <A HREF="http://www.hypermail.org/">hypermail 2b29</A>
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: <EM>Sat Mar 31 2001 - 08:32:47 PST</EM>
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