[sane-devel] pixma: no gamma table in TPU mode

[Valentin David]

I had troubles making the gamma correction to work in transparency
unit mode on my Canon 8800F. Since the problem appeared both on
xscanimage and XSane, I thought it was probably the driver. So I
looked the driver source, and understood that in TPU, the scanner does
not get any gamma table but rather sends 48 bits data.

I also discovered that it was using a gamma table in flatbed mode. I
tried, and then it does work. Which confirms the thing.

This is great to get raw data. However it seems that the gui frontends
do not tell you cannot set a table. And also, I cannot use GIMP
directly. On underexposed or overexposed films, I get quantization
artifacts. I need to reinstall CinePaint. :(

In XSane, the color correction also gets strange. I do not know if it
is related. The red looks overexposed, green OK, and blue under
exposed.

Certainly the driver needs to say if the gamma correction will be done
or not. And the frontend should apply it on its own if there is no
correction done. At least for the user not to get this unexpected
behavior.

-- 
Valentin David
valentin.david at gmail.com