Change image mode to RGB
If you're trying to change the Hue/Saturation (that's one way to change the colours on an image) on one of your PNG or GIF images but you keep seeing the error message
XYZ operates only on RGB color layers.
XYZ does not operate on indexed layers.
Go to Image ➔ Mode ➔ RGB.
- credits pgimeno on #gimp @ freenode
Retrieve missing toolbox
Go to Edit ➔ Preferences ➔ Window Management And then click on Reset Saved Window Positions to Default Values
Create hotkeys for commonly-used functionalities
Go to Edit ➔ Keyboard shortcuts
Switch to single-window mode
Go to window ➔ Single-window mode
Make selection transparent
Make sure your image has an alpha channel
- Go to the layers menu, right-click on the layer and choose Add Alpha Channel
Select the area you want to make transparent and hit delete (not backspace)
Extend a layer to make the background larger
Increase Layer Boundary size (Layer ➔ Layer Boundary Size)
Adjust Canvas Size
- Either (Image ➔ Fit Canvas to Layers) or adjust it manually via (Image ➔ Canvas Size)