Some are color-based, others do some kind of blur or texture-mapping. They did a really nice job adapting photo filters to touch here. Take a look at how you can scrub through the black and white filters and change how the photo gets converted to black and white. This is such a neat interaction.
Finally, we’d be remiss if we didn’t call out the photo inspector modal. It mimics a pro camera’s LCD readout — drop-dead gorgeous.