So actually the original scene in reality must be in (color) balance to remove a color cast by an automatic color balance filter.

Perhaps, but not with this photo... It sees a green color cast because the picture mostly contains green. So the correction removes some green and makes a purple footpath.

This is the danger of all-automatic correction (which, whatever the algorithm, more or less tries to make the average picture grey). It doesn't work on pictures that have a natural dominant color: forests, sea, sunsets... and indoors, the color of the walls... I've ruined gorgeous sunsets because my camera was set to auto white-balance... When you want to nitpick, very few pictures are truly grey on average, you have to find a part of the image that should be grey (pro photographers put a grey sheet in one of the pictures, but you can often find something that should be grey/white: paper, porcelain, shirt, clouds...) and use that to compute a correction for the whole picture. This is for instance how that script works.

thanks iarga.
I will prepare it for release. Maybe I add an option to let the user choose the first (strong) instead of the last (moderate)

Thank you iarga and ofnuts. I've learnt it just now about colours in a photo. But it's my blame not to have chosen the right photo, so it's important that the users know on which kind of photos can be applied the filter.

Issabella, your original green forest image has probably no/very little color cast. So it needs perhaps no color correction. But yes that image can use more contrast.

I see automatic color correction tools more as aid, to have a quick preview that gives me clues how to (and how not) correct the image. So I see automatic correction as a way to analyse an image. Sometimes it is a start.

Above all, trust your own eyes. If an image looks like reality, it has probably no/little color cast. And if you change something, then see if it corresponds to reality. Try to find the neutral parts of an image, as ofnuts said above here. Try to make and let them stay gray/neutral with every correction.

Dinasset, now I'm curious for what you think about automatic color correction. What's your use for it?

IMO it can be used when:
- there is a real colour cast (not a dummy one...); your eyes can judge...
- it's an almost very well colour-balanced image, not a subject having per se a too predominant colour, I mean predominant in the real life; if I take a picture of fires, obviously the image is "reddish", but red shouldn't be removed/compensated.
I will have very few occasions to use it myself for my photos.
It's anyhow a "specialized" tool, not a simple enhancer tool like many others.

Thank you again iarga. I learn from you and people as you who know so much of photography. I'll have in mind what you have told me and I'll let my eye value these aspects on the results if applied.

Newest version is now available at Gimp Scripts.

Thanks, Rod.
Those who are interested in its functionality should download the enhanced version.
Changes introduced in this release:
- fixed a bug (flatten was wrong, merge_down now used)
- added user's choise between Full or Moderate effect
- Moderate uses mid value instead of avg
introduces a percent of application (internal)
adds a dup+pixelize+invert and overlay

You may have here a look at the different outcomes between Full and Moderate

The last test version did, but in 1.1 I don't see this layers. Is that right?

merged down

Ok

I think it is very nice for an automatic white balance