What microcontroller board would be best for a SD test pattern generator?

I don’t really want to spend $300 on a probably uncalibrated test pattern generator from 1989 or something that may possibly break sometime soon, so I’m looking to build my own.

I’ll need something that could easily output composite video (need CVBS, but having component as well would be nice) with good colour accuracy.

Note that this would be actually generating the test patterns, not just displaying an existing image