This really is an amazing piece of work by the masters at Platige image

And here’s the making of. Alas it gives very little away.

There’s making of material at behance. If you scroll down to the technique section it shows some breakdowns of their painting technique

These are the guys who made the awesome paths of hate that won the Jury award at Siggraph in 2011.. . There NPR technique is excellent . Go check out the vimeo channel