I've looked at a couple of previous questions, but I haven't been able to apply it to my question.
I'm trying to extract the black from this picture (so I can turn it into a vector later in Illustrator):
One answer to this previous question suggested fiddling with the input levels, but mine don't look as nice as the ones they show and I can't find a setting where white is totally white and black is totally black.
When I add an adjustment layer converting it to black and white and I try to place it into Illustrator, I get this:
I've also tried following this answer's suggestion and do
filter | stylize | find edges and I'm getting close, but I don't have optimal results yet: