Call me stupid!

Software GIMP
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#1

Long time user of Gimp, DarkTable here (on Linux) and I’ve always, literally ALWAYS struggled with colorcasts. Somehow managed to do post but some images were just too bad to correct.

Yesterday, my wife asked me to shoot her and her horse and we found a couple of nice places to do so. Overcast but very bright summer sky and dumb me planted the pair below some neat trees for background with a horrible green cast as a result.

I did not want to let this cutesy pic of them go to waste and my wife loved the expression of love and trust between animal and human so I promised to do my best.

Came across this Youtube tutorial which is so straightforward and easy to use, it’s almost embarrassing I didn’t catch on over the last 15 years or so. https://www.youtube.com/watch?v=gr692iyYBUI

Filters/Blur/Pixelize? Of all filters? I do not think I have ever in my wildest dreams found any use for it ever before.

EMG04094-Victor-ISO800-comparison-2020-web
EMG04094-Victor-ISO800-comparison-2020-web1050×1402 1.26 MB

stars turn blue - darktable - white balance issue?
#2

He, Pixovert, made an updated version of that video. The one you linked to is an old one for GIMP 2.6, this one is the updated version for 2.10

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#3

I think this method can be a start to correct colors. In your correction the horse now has a bluish/magenta nose and hips.

So I recommend you to use curves thereafter or right away, so you can treat the darks, mids and lights more separated. Here is a nice tutorial:

#4

I much prefer the top image, much more pleasing colours, and the green cast is not too strong.

That said, have you tried using channel mixer to eliminate casts? A green cast would be handled in the green channel. Reducing any of the r,g,b sliders will make that particular colour more magenta - the opposite of green.

A method I like in Photoshop is to make a solid colour adjustment layer, the colour a sample from the image (using dropper) you wish to be white, blend mode set to divide. If this makes the image too dark or light, then select a lighter or darker shade of the same colour. I don’t know if this is possible in gimp, but it is said to be the photoshop alternative and this is a fairly simple operation, so I assume so.

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#5

Hi Stupid! Dumbo here.
[Wasn’t that a suitable start???]

Thanks for reviving that method, which I had quite forgotten.
One of the dilemmas having access to such a multitude of splendid software is that it is utterly impossible to remember each and every module, what this or that method is good for, &c.

I have started to keep notes: to enhance white clouds, do … &c.
Works quite well! If ever I remember to look there…

Have fun!
Claes in Lund, Sweden

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