Is programmatically inverting the colors of an image possible?

Question

I want to take an image and invert the colors in iOS.

Answer 1

Sure, it's possible-- one way is using the "difference" blend mode (kCGBlendModeDifference). See this question (among others) for the outline of the code to set up the image processing. Use your image as the bottom (base) image, and then draw a pure white bitmap on top of it.

You can also do the per-pixel operation manually by getting the CGImageRef and drawing it into a bitmap context, and then looping over the pixels in the bitmap context.