[sane-devel] Half-stepping on the vertical axis (Epson RX500)

[ljlbox at fastwebnet.it]

I have got an Epson RX500, and I'm using SANE 1.0.15 with the Epson Kowa
backend (but I'm positive this all applies to the SANE Epson backend, too).

My scanner is 2400 dpi horizontally but, like most flatbed, can half-step
the motor to get 4800 dpi vertically, and I am interested in that.

Unfortunately, the backend only supports symmetrical resolutions. I have
tried hacking around in the source, but got to nowhere: I can get the scanner
to half-step by modifying the set_resolution() function, but then scanimage
fails with an I/O error.

That's quite natural, since the backend still believes it's going to get
a 2400x2400 image (or 4800x4800, depending on the type of hack).

The key would be to have the backend realize that it's going to receive n*2
pixels from the scanner in the vertical axis (on n/2 in the horizontal axis,
whatever) -- but I haven't been able to pinpoint the right place(s) in the
source for changing this.

There are a few resolution-related variables in the source: ndpi, s->val[OPT_RESOLUTION].w,
pixels_per_line, x_max, y_max, and so on. I've made a few attempts at modifying
some of these, but with no success.


Thanks in advance to anyone who can be of help.

by LjL