[sane-devel] imageClass bug

Ralph Little skelband at gmail.com
Sat Nov 14 07:03:06 GMT 2020

I am hoping to garner some opinions about an issue that I am having with
testing a Canon imageClass machine with the pixma backend.

I have an imageClass MF4770N machine that has always been a little
problematic on the ADF and I have never really understood why.
With Rolf we managed to get the machine fairly well supported but
sometimes the machine would fail with a service code and abort requiring
a power-cycle.

I recently managed to track down the specific behaviour that caused this
issue but I am not sure how to deal with it.

When scanning on the ADF, if the user selects a scan area that is
aligned to both the hard left and hard right of the scan area, then the
machine scans OK. However, if the selection is away from the left area,
the selection can not extend within 32 pixels of the right hand side.
Within that restriction, I can scan whatever I want.

In order to scan a selection that aligns with the right hand side, the
select must align with the left hand side also.

This, I think is a bug in the machine's firmware. I just checked and it
is fully up-to-date so it looks like there are no fixes coming.

On Windows, when using the ADF, one can only select a fixed media type
that is centred in the scan area. One cannot arbitrarily select a scan
area. So it is not possible to see what the Windows driver would do
because the scenario is impossible.

My problem is how to deal with the issue in the Pixma backend. The
common scan scenario in ADF is to scan Letter media which is a full
width scan. I cannot just make the maximum width 32 pixels less to avoid
the problem. In 75dpi, 32 pixels is a significant chunk to miss from the
right hand side.

Any ideas?


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