Tilt-shifting is a photographic technique involving the physical rotation (tilt) and translation (shift) of a lens with respect to the imaging plane. The result is a picture with warped perspective or selective focus. A particularly cool use of lens tilting lets us simulate a miniature scene from a photograph of real-world scenery.
Lacking a tilt-capable lens, we can use digital post-processing techniques to emulate this effect. I found an article that gave an example on how to do this with a blurring function:
blah blah blah MATLAB code newline tests Dear Qifan: finish this