[sane-devel] ADF Duplex performance problems

[Simon Matter]

> On Sun, Apr 25, 2010 at 4:45 PM, Ilmārs Poikāns <ilmars at delibero.lv>
> wrote:
>> Hi,
>>
>> I'm running latest SANE from git source on Ubuntu 9.10. I was testing
>> scaning A4 on Fujitsu ScanSnap 500 in 300 dpi Color uncompressed using
>> scanadf. Everything is fine when scanning only one side of sheet (image
>> size
>> 24MB). But when scanning with "ADF Duplex" as source, scanner pauses 3
>> times
>> during scanning. Two 24MB files are saved successfully. Clearly pausing
>> is
>> caused by data transfer issues somewhere.
>
> Does this happen on windows?
>
>> Any ideas where could be the
>> bottleneck? Scanner can't send data so fast over USB?
>
> Almost certainly.
>
>> Buffer too small for
>> USB transfers, so too many data exchange transactions creates delay and
>> slowdown of throughput?
>
> You can try increasing the buffer-size option in /etc/sane.d/fujitsu.conf.
>

The config states:
# to set data buffer size, in bytes
# the value ranges from 4096 - infinity
# but you may have scanning problems with
# a value larger than 65536 (the default)
option buffer-size 65536

I'm just wondering what kind of scanning problem may I have with bigger
buffer-size? Does it still apply to version 1.0.21?

Simon

>> I guess scanner is sending data from duplex scan
>> interleaved - data block for front side, data block for back side.
>
> for the low-memory scanners like the S500, yes.
>
>> Inefficient processing of such data in fujitsu-backend? Maybe problem
>> caused
>> by scanadf (or any other frontend), that can read images only one by
>> one?
>> Any ideas?
>
> as long as you have enough ram in the system to buffer the back side
> image, the backend can usually outrun the scanner.
>
>>
>> What is the status of SANE 2.0? Is there any functionality for
>> retrieving
>> many images simultaneously from one physical scan, like front and back
>> of
>> page during duplex scan, several image regions on pages?
>
> neither of those have been discussed for sane 2.0, but the
> 'multi-region' idea is probably a not going to happen. The first idea
> actually is already supported by the fujitsu backend. The 'low-memory'
> option causes the backend to do alternate transfers if required. You
> have to inspect the value of the 'side' option before each transfer to
> determine which image the next block will be for. This is only useful
> with a custom frontend, as nothing commonly used will support it.
>
> allan
> --
> "The truth is an offense, but not a sin"
>
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