[sane-devel] Re: Feature freeze for sane-backends 1.0.13 is active

Varol Kaptan varol@cs.ucf.edu
Mon, 3 Nov 2003 04:34:45 -0500

Hi everybody,

First, I would like to report a problem with the epson backend on a
Perfection610. As far as I can see the color scanning for this scanner
has been screwed for some time now (including the latest 1.0.13-pre1).
This problem goes back to 1.0.9 (at least - probably much earlier).
Color scanning on this model requires some color shuffling of lines.
Sometimes when I use scanimage to generate a ppm, the ppm will have
less data than required and xv would complain about a truncated file -
at other times the size would be ok, but the first few lines will have
wrong colors (there will be a vertical offset between color channels).
The epkowa backend does not seem to have this problem. I was able to
partially fix the latest epson backend (no more truncated files, but
still the other problem). I'll keep trying but in the mean time I would
like to hear if anybody else has similar problems (I can provide test
cases if you are interested).

The second problem I have is the following: It seems like the epson
scanners can only scan areas with a width which is a multiple of 8.
When I scan a 1in x 1in area at 600 dpi I get a 600x600 ppm (that's
fine). When I scan the same area at 300 dpi, though, I get a 296x300 ppm
instead of the 300x300 (since 300 is not a multiple of 8). It turns out
that the driver will round down to a smaller value that is a multiple
of 8 - I thought that it would be more appropriately to scan 304x300
and then cut off the excess. The easiest way to do this is to have for
example bytes_per_line=3*304 and pixels_per_line=300 (padded image
format) and I have a working version (modified epkowa, but same applies
to epson backend). If you look at the developer documentation (latest
sane.ps, bottom of page 29) you will see that frontends are supposed to
be able to deal with such padded image formats. Unfortunately none of
the frontends (I tested scanimage and xsane) do support it. Is this a
bug in the frontends or in the documentation (i.e. should the frontends
be fixed, or should I forget about padded images) ?!?