Without having had a proper look at your code, my guess would be that the reason for it being slow is probably the fact that getting / seting single pixels in rasters is quite slow at the moment. There are a few reasons for this: I cannot directly access the image's data buffer, so I have to transfer pixels back and forth, using an SDK function. This function can be used for transfering bigger chunks, but then the caching overhead becomes complicated. So at the moment, this function is used for transfers of single pixles, which most probably is very slow.

One possibility to make it faster right now would be to retrieve the whole image as a BufferedImage, then work with that, and at the end create a new Raster from it. I am not sure about the implications of color conversion here though.

Thankyou for your replies. I've had a rest from this, but coming back to it it's pretty obvious where the problem lies. While running the code I can see how long each section takes from what gets printed to the console, and the bit that takes stupidly long is this. It's just a silly number of embedded for loops. Oh well, I think I need a better algorithm!

for (x = 1; x