[sane-devel] ADF Duplex performance problems

[m. allan noah]

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.

> 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"