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

Valentin David valentin.david at gmail.com
Sat May 22 18:06:21 UTC 2010

I actually discovered that XSane can do the gamma correction in
software. However you have to manually uncheck a box. It should
automatically detect it cannot send a gamma table, but fails. Is it
the mistake of XSane or of the driver?

On Sat, May 22, 2010 at 6:35 PM, Valentin David
<valentin.david at gmail.com> wrote:
> 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

Valentin David
valentin.david at gmail.com

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