[sane-devel] inactive options / xsane

[Tobias Richter]

Hi, 

I have a Brother ADS-2100 scanner using the brother4 proprietary driver.
Sane reports the brightness and contrast options as inactive while in 
colour mode (24 bit or 24bit fast). 
That means I cannot contols those options and hence my colour scans from 
scanimage, scanadf or through the python bindings are poor quality. 

Surprisingly xsane happily manages to control these "inactive" settings
in colour (and gray scale) mode. A brief look into their code showed 
they even have a per colour channel setting (red, green, blue). Maybe
that's their trick? Unfortunatly I couldn't easily figure out how these 
settings are applied. 

How does xsane manage to do what the library refuses to do?
Why can't the command line tools to the same thing?
Or why can't the library handle this transparently for the application
(if the trick is in separate settings for each colour channel)?

Thanks,

Tobias