[sane-devel] Canon-SCSI backend

[Diego Zuccato]

Deiters wrote:

> thank you for the tip about the array length; I will check this.
I "hit" the bug some time ago (around 25/10), and Henning Meier-Geinitz
found it.

> The FS2710 does not seem to be influenced by downloaded gamma tables.
Yep! It is. Or at least I've had MAJOR troubles when trying to adjust
gamma by HW (about one year ago, IIRC).
Then xsane started using SW gamma and the problem was gone.

> The original Canon (Windows) software feeds it 4 tables of 8192 byte
> length (2^12 entries of 2 byte length), but does not change them
> when you manually select another brightness, contrast, etc. .
It should change them when you alter gamma table. Brightness and
contrast are a different matter and never gave me troubles.
> My guess is that Canon runs the scanner in 12-bit mode all the time,
> does the gamma correction in the computer, and then rounds the result
> to 8 bits.
Maybe. I really don't know enough details to tell what happens - and
haven't windoze to test.

> Our Canon backend does just that, and the results look the same as
> those obtained with their software.
That's good. IIRC, the problem was present when acquiring in 8-bit mode.

> Incidentally, the Canon backend contains subroutines for the
> adjustment of contrast, brightness, shadow point, etc., that others
> might find useful.
Shouldn't those be done by the scanner itself, so to use the full range?
Is multi-pass scanning supported? (well, not just sending more times the
"scan" command, but acquiring a line multiple times before moving head
to the next).

BYtE,
 Diego.