Advanced GIMP selecting in landscapes

Software GIMP
1

Often, what I’m trying to accomplish involves a strategy for selecting some element. (This is why I like luminosity masks.) However, I have many outdoor shots where I need to separate foliage or other items from the sky. Here are two ideas I’m considering for images like that in the link at the end of this post.

One is to exaggerate the color, then use Select by Color on the blue sky, then invert the selection, then save the selection to a path, then return the color to normal, then use the saved selection to make changes only to the trees I want to highlight.

The other is to use Threshold or similar density-based tool, since the trees are usually darker than the sky. Then base a selection on that, save it as a path, reverse the threshold effect, and use the saved selection to work on trees (or invert the selection and work on sky).

One repeat problem with such experiments is the transition from branch to sky. I mention it because this zone and how natural it looks will determine the usefulness of a selection technique.

Any comments that might save me a lot of time?

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You could apply a tone curve to help exaggerate the contrast, then use a luminosity mask.

You could also try to posterize the image and make a selection based on that.

You could use wavelet decompose if there are sharpness differences.

You could split the image into it’s RBG channels and select from there.

3

I feel your pain. This is a hard thing to mask for sometimes. I’ve personally had good luck with a combination of color decomposition (try a couple of options to find one that best isolates your region) or a luminosity mask if it’s well defined.

Couple that with some feathering and/or shrinking to tune the transitions… wish I had a better suggestion. :frowning:

1 Like
4

Everything @patdavid said!
I guess @patdavid you are using your color channels as mask and choose the one which exhibits the highest contrast in the area you need, right?

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Something often overlooked is that the color selection can work on other criteria. In this picture the sky is easily selected using the Hue.

However the color and fuzzy selection tools are all-or-nothing, you don’t get the partially-selected pixels that would make your selection look natural. For this you would need the foreground selector as implemented in 2.9 (or on some forks of 2.8).

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@patdavid I had never used decomposition for anything other than LAB. Cool.

@Ofnuts I just had a RTM moment. Opened GIMP to see what you were talking about on the color select tool, and oh look there’s a dropdown labeled “Select by” and one option is Hue. This resembles my tunnel-vision use of the decomposition option, yes?

And the foreground selector is something I will chase down.

Thanks all!