Making a Selection from a Channel

[cloudescaper]

Hi there, thanks for reading this!

I have an image (layer) in b&w  I want to use as a mask. In Photoshop, I used to make sure the layer is active and just press "strg+alt+2" or make a selection from the RBG or Green channel in one click. This gave me a selection that is hard in the bright white areas and softer in the areas where the light is less bright. I used this simple method to edit the highlights in my images with absolute precision, since I can paint on the b&w layer and exclude certain areas as well. It was so quick an easy and I was wondering if there is fast way to get the same selection out of gimp?

Thank you in advance

[Ofnuts]

(Yesterday, 11:23 AM)cloudescaper Wrote: Hi there, thanks for reading this!

I have an image (layer) in b&w  I want to use as a mask. In Photoshop, I used to make sure the layer is active and just press "strg+alt+2" or make a selection from the RBG or Green channel in one click. This gave me a selection that is hard in the bright white areas and softer in the areas where the light is less bright. I used this simple method to edit the highlights in my images with absolute precision, since I can paint on the b&w layer and exclude certain areas as well. It was so quick an easy and I was wondering if there is fast way to get the same selection out of gimp?

Thank you in advance

This is a "luminosity mask". The most basic way is to open the Channels list, right click one of the R/G/B channels, and "Channel to selection". You can get more fancy, making a grayscale version (Colors > Desaturate > Desaturate or Colors > Components > Extract components and pick a relevant component (LCH luminosity, for instance)), taking any of the RGB channels, and then applying Curves to select a specific range. There are even scripts for this, for instance my own ofn-luminosity-masks.