When BS.Player uses FFDshow you can simply set FFDshow's 'Postprocessing Level' under:
(rightclick >) Options > Properties > Video > FFDshow properties.
There you can slide 'postprocessing level' (option at the top of the window).
Another option is (with an appropriate videofile loaded):
(rightclick >) Options > Filters > Advanced
Then click on the [+]-sign in front of
'ffdshow Video Decoder' and subsequently click on '
ffdshow'.
In the 'column' in the middle of the window
(actually it is the column at the left of ffdshow's video decoder configuration screen) there is (i.a.) the option
[ ] Postprocessing 