Recently needed to manually edit the pixels on a UIImage so i could apply, in my case, a colourising filter ("colorizing" for most of you reading this!)

Anyway, couldn't find many good tuts on the web, so here we go with my code. Tested and works great in xcode 4.2 / iphone.

Here's my end result. You may recognise a yamaha FZ1N. Lovely bike, wish i'd never sold it:

And here's the code: