I currently have a PIL Image object which I store as an array of bits (1's and 0's). However I now would like to be able to rotate that image 45 degrees. One way to do it is take the original PIL image, apply a transform matrix on it, then convert that to an array of bits. Problem with this approach is that it's computationally expensive, especially if I want to start doing more than just one rotation. It would be faster to just modify the array of bits directly.
I tried using numpy.roll:
numpy.roll(bits, 45) # rotate 45 degrees
Unfortunately, this just does a circular shift, not an actual angular rotation.
What algorithm can I use on the array of bits to give me the desired output without having to go through the original image? Even though my application is in Python, your answer can be in whatever language you feel comfortable with, I'm more interested in the algorithm itself not the syntax :)