Comprehension issue

[Richie1027]

(12-12-2023, 05:38 PM)PixLab Wrote: A layer mask is to mask (hide) or show the image at the level it is or the image below.

Click on the screenshot to make it bigger


In this example 2 layers (normal layer) and 1 layer mask attributed to the top normal layer
I did draw a black and white gradient on the mask (AKA Layer-mask).
as you can see the white part of the gradient shows the top layer where the mask is
The black part of the gradient shows the layer below
Pretend that the white part of the mask is the "light" and light up the layer part (the top one), here the rainbow on the left side
Pretend the black part of the mask id the LACK of light, it's darkness, thus it does not light the right part of the rainbow, so you can see below it (the layer below)

the white is the light => Opacity because you cannot see thru (on the left)
the black is darkness, no light = Transparency because you can see thru (on the right part)

in the middle it's different gray scales, thus it's half transparent more or less depending how dark or clear is the black and white gradient

I hope this help, not sure I explained intelligibly

Thanks so much.  Your example did help solidify some of my understanding. The mask concept makes sense but I believe it’s the white being called opaque and black being transparent that has thrown me.  I’ve done a bunch of tutorials from YouTube and nearly all use a layer mask (mostly white but some to selection).    I’m trying to visualize these layers stacked.  And deciding on what type of layer mask becomes more confusing.  Instead of white, why not black?  Or when would you use a black layer mask.

I’m not throwing these questions at you…. I, appreciative for the time you took to reply;  I printed your text to add to my own training.  I’m going to keep looking for some paradigm that explains it in a way I can grasp.

Thanks again

---

I had a reply from another gimp user: he wrote
Want to change a human iris to a cat's iris?
Place a mask on the layer. Erase the iris.
Create a new layer. Draw the new iris.
Turns out you like the human eye better? Fine.
Turn off the cat's iris layer. Now disable the mask on the original artwork. Viola.

If this makes sense to anyone, let me know how you knew which TYPE of layer mask to use! For example, when you knew you had to erase the iris, how did you know which layer to pick?
I’m going to play with this idea with a couple photos