How to pixelize / add pixelating effect to a UIImage in iOS

I am looking for a way to pixelize a UIImage in Cocoa touch. I don't know what the best approach would be (some people have suggested me using OpenGL) but I have a feeling there must exist some other simple way I may be overlooking.开发者_StackOverflow中文版 Does anyone know of one?

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Signal processing explanation of what to do to the image:

1. Downsample by N
2. Upsample by N
3. Then convolve the image with a NxN box filter (Matlab code to create NxN box filterrect = ones(N,N)).

Comp sci explanation:

1. create an empty new image that is the same size
2. iterate over every Nth pixel in the original image
3. repeat every Nth pixel in the new image