GIMP is an advanced image editor and you can use it to add transparency to an image. The process is going to be a bit different if the image you start out with isn’t a PNG. In some cases, the process can also be a little tricky even if you have a PNG file. This is because of something called the ‘alpha channel’. This is where transparency is stored and if it’s absent, GIMP won’t be able to make the image transparent. The fix is simple.
Add transparency to image in GIMP
Open the image in GIMP. You should have the layers window visible. Select the layer that the image is on, right-click it, and from the context menu, select ‘Add Alpha channel’. Now, when you erase part of the layer it will be transparent.
This is the first step to adding transparency. The second is when you save the file. First, you have to save the file as a PNG, TIFF, GIF, BMP, or JPEG 2000. These formats are capable of preserving transparency. Go to File>Export As, and select PNG.
When you click Export, you will see a smaller window which you should not ignore. There’s an option here that’s checked by default called ‘Save color values from transparent pixels’. Uncheck it, and then save the image. This is what’s going to make sure that the transparency you added to your image is properly saved.
If you have a lot of empty space around your image, and you’d like to delete it, go to Image>Crop to content. This will crop all the empty space from the four sides of the image without cutting out any part of it. You can do this manually with the crop tool but it will take a few more tries than with the option in the menu bar.
If you’ve gone from using Photoshop to GIMP, you’ll find this is a small difference between the two apps. Photoshop doesn’t assume that people know what an alpha channel is or what it’s for. GIMP does, and it doesn’t seem to think that adding transparency might be a common need even though lesser apps like Paint.net support it as well.
If you later decide to edit the image again, whether you use GIMP for it, or you use another tool, make sure you’re mindful of the transparency and the alpha channel being preserved once you’re done editing. You should make sure that the app that you’re using also supports the alpha channel.