Bokeh and how to fake it.

Bokeh Tricks in Scott Pilgrim

Start with a 16-bit picture (8 will work too, but for mathematical reasons you’ll get better results with a raw image) with really sharp well-focused point sources of light (street-lamps, christmas lights, ferris wheel bulbs) and then run a “Filter->Shape Blur” on the part of the image that you want the custom bokeh effect to show up in.