You can cut the excess background off, I use GIMP for tasks such as that. With the gimp tool it is easy, select the area you want to keep, go to Menu Bar->Image->Crop to Selection and BAM! Excess transparency is gone.
Or you could download my Image Transparency Addeer/Remover scenario. Just run, load and save. It will automatically reduce it to minimum image size. It is located here:
http://www.greenfoot.org/scenarios/7423
A new version of this scenario was uploaded on Thu Aug 07 15:39:48 UTC 2014
Added a Choose Cat screen, you can now choose between three cats to play as.
A new version of this scenario was uploaded on Thu Aug 07 18:10:31 UTC 2014
Added more characters!
I tried your scenario danpost, however it didn't work for gifs.
A new version of this scenario was uploaded on Thu Aug 07 19:57:56 UTC 2014
Updated the character choice screen: I removed gif animation and replaced it by scaling the images up when moused over.
A new version of this scenario was uploaded on Sat Aug 23 00:18:54 UTC 2014
You now have to pay for your characters! Buying saves, so you only have to buy once.
A new version of this scenario was uploaded on Sat Aug 23 00:58:57 UTC 2014
You now have to pay for your characters! Buying saves, so you only have to buy once.
A new version of this scenario was uploaded on 2015-02-05 20:45:22 UTC
2014/8/6
2014/8/6
2014/8/6
2014/8/7