The free GIMP image manipulation program does exactly what it says, but for a beginner like me with a single task that I only need to do occasionally, it can be confusing. You can download the application from http://www.gimp.org/ and there are versions for Mac and Windows PC (maybe others too).
The following instructions give a quick guide to making logos fit the Firkin App ideal specification:
- Open GIMP and make a new image 256 x 256
- Add a new layer: Layer/New Layer command and make its fill Transparent.
- Now File/Open As Layers and open the target image
- You may need to scale it up or down: Layer/Scale Layer so that its largest dimension is 256 px. You may also need to select a relevant part of the image and crop it and then scale
- Make sure that the layer has an Alpha channel: Layer/Transparency/Add Alpha Channel
- Select any coloured background outside the outline of the logo using the Fuzzy Select tool
- Delete the selected coloured background
- Repeat the above two steps (6 and 7) until white/black/coloured background outside the logo's outline is cleaned up
- Export the file as a png file: File/Export As and then confirm Export - make sure there are no spaces in the file name!
- Now you can delete this layer using Layer/Delete Layer and move on to the next target image in step 3
- Repeat until all of your logos are in the ideal format