Let’s say you have this cave image on a transparent background:
You need to make a black outline around it — this can be used, for example, for a parallax effect in a game. Let’s get started…
1. Create a mask: Layer → Layer Mask → From Transparency
2. Alt + click on the mask (so that a border appears around it).
3. Press Ctrl+I — invert the mask.
4. Right-click on the mask → Apply Layer Mask.
5. Now apply contrast to this shape, and you’ll get clear cave contours on a transparent background.
Hallelujah! We now have a black outline that works perfectly for creating a parallax effect or overlaying on top of other layers in a game.