Gimp For Software Developers: Troubleshooting and Quick Tips

Gimp version used: 2.10.18

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.

or

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

PNG image used

• Make sure your image has an alpha channel

  • Go to the layers menu (right-hand side of the screen), right-click on the layer and choose Add Alpha Channel

• Select the area you want to make transparent and hit delete (not backspace)

Add alpha channel (if your image has none) and hit DELETE

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)

Apply blur to selection

• Select an area using any selection tool

• Go to Filters ➔ Blur ➔ Gaussian Blur

Downscale images without loss in quality

Make sure you set the image mode to RGB rather than Indexed, before you scale your image down.

• Go to Image ➔ Mode ➔ RGB

• Then go to Image ➔ Scale Image to do the scaling

References

• StackExchange Graphic Design: Scale down an image in GIMP without losing resolution

  • I've used this answer to solve my problem, but there are others too.