On Thu, Nov 17, 2005 at 01:10:19AM +0300, Alexandre Prokoudine wrote:
> On 11/17/05, Timo Steuerwald <[EMAIL PROTECTED]> wrote:
> > Hey, that's a cool feature! Thanks a lot! I didn't know that up to now,
> > but anyway: How does this automatical white balance work?
> I don't know how exactly this engine ticks, but I can to to guess: it
> searches for the lightest pixel in the image and makes GIMP believe
> that it is white and then it shifts other colors appropriately. But
> that's my guess. Probably gimp-help package contains information you
> want to know.
I'd like to understand it better too, if someone has an actual explanation
or links to documentation, please post (I searched a bit for gimp white
balance ... not much in terms of explanation)).
I think the auto white balance is the same thing as Tools -> Color Tools
-> Levels, then select "auto", but you have flexibility with the levels
It looks like the auto leveling just sets each color such that they are
evenly distributed, by setting "dark" and "light" tones (that is what the
help menu calls them) such that they are at the low and high range of where
each color shows up. Just play with it some and you can see what I mean ...
Read this for a good explanation on using the level tool:
Try auto leveling, and then look and play with the setting for each of the
three *color* channels (i.e. not the default "Value" channel, auto does
not modify it). I'll often adjust the values towards their original values
in order to get more accurate colors.
This must be similar to in-camera auto white balance. And even the
in-camera auto white balance is sometimes wrong (and probably why you are
trying to fix this in gimp ... or maybe you picked "sunny" white blance, and
forgot to switch when moving indoors under incandescent light).
It would be nice if there were gimp level settings like "cloudy",
"tungsten" etc., like we have for dcraw, but I guess those can only be
applied to raw images (or to images with no modification to their white
balance), else it would be somewhat a useless.
-- Patrick Mansfield
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