Black pattern consists of flashing bars on the black background with luminance levels from 2 to 25. The goal is to set TV brightness as low as possible while level 17 still flashes. However, whatever brightness is set on TV, bars 2-17 never flash. After increasing brightness to +1 in control panel level 17 begins to flash, but level 234 on white clipping pattern stops flashing. That seems like level 17 of 16-235 range is outputted by driver like level 16.
The above was tested on HDMI output with Panasonic TX-P50ST30E plasma and Samsung LE32D550K1W lcd on Win 7 x64 with plenty of software players (VLC, MPC, Potplayer, Kmplayer). Driver version is 22.214.171.1249.