What software do you use?

Well from my digital image processing class I attended just some months back, we used a java based image processing software called imageJ. ; It is not your regular tool though as you have to write the code for which effects you want to appear on your picture. ; For example, you want to perform a gaussian rotate, you have to design an algorithm that would alter each pixel and make the rotate possible.

While this would be a big step for regular enthusiasts, those with programming background will surely find this entertaining and useful as well.