[sane-devel] Why does XSane set Gamma = 1.0

Oliver Rauch Oliver.Rauch@Rauch-Domain.DE
03 Sep 2004 13:46:49 +0200

Hello Ullrich,

the preview scan is done with no color correction (gamma=1.0,
contrast=0.0 and brightness=0.0) to get the original data from the
scanner. The color corrections (gamma, brightness and contrast) are done
before the image is displayed in the preview window.

When the user changes the color correction values then xsane can display
the corrected image without having to scan the image again.

If xsane would apply the color correction values before/while scanning,
then the user would have to do a new preview scan each time when he
changes the color correction values. That is what xscanimage does and it
is not very comfortable.


Am Fre, 2004-09-03 um 12.22 schrieb Ullrich Sigwanz:
> Hello all, 
> Hello Oliver (Rauch) in particular,
> I have a (may be silly) question:
> Why does XSane set the scanners' Gamma Table to an equivalent Gamma of 1.0
> before a preview scan is started?
> Background:
> NIASH scanners work best with a gamma value of 1.6. 
> Gamma=1.0 will definitely produce scans that are far too dark.
> A workaround is: 
> troughing away the feely editable gamma-table in the scanner options and
> only offer the analog gamma correction scalar, so that the gamm table cannot
> be changed.
> But this would take away a degree of freedom, that might be useful for some
> users.
> On the other hand:
> Using the scanner with a gamma that is definitely bad, is also no good idea.
> Especially for "Newbies".
> Thanks your for your answer
> Regards
> Ullrich