Remember that I started out by developing a camera app. The tool that allows you to apply effects to existing photos was only written so I could tweak and test the effects before putting them in the camera app so I developed it on a desktop machine so I wasn't really concerned with performance. At the moment a 480x320 preview image takes about 5s to process on the N900. I am yet to try it with a full size image. I have no doubt that the N900 can do it but I will probaby need to optimise the code a bit to make it usable.