[sane-devel] canon 2710 slide ...

[Deiters]

I am pleased to see that someone is still interested in the
FS2710S!

I have the overexposure problem, too. It is not always evident,
however. I guess that 99% of my slides are scanned well, but
clouds and a blue sky, or a bride in white dress are problematic,
indeed.

The FS2710S does a self-calibration after power up, but that is
not the cause of the problem.

I had a look at the SCSI traffic and found out that the Canon
software transmits gamma tables before each scan. Unfortunately
I was not able to intercept the contents of those gamma tables.
There seem to be 4096 two-byte entries for each color channel,
low byte first. But so far I have not been able to store a gamma
curve myself. As also the contrast and brightness controls have
no effect, I suspected that the FS2710 has no software control of
its digitizer, and that all color corrections must be done by
software (this is done by the recent backend).

However, the Canon (Windows-based) software does not have the
"overexposure" problem,  and this proves that my assumption is
not quite correct: The FS2710 does have some software control,
but I do not know how to activate it. I would be grateful for
good advice!

Sincerely yours,

Ulrich Deiters