i'd been googling for answers for this, all guides point me to make it grayscale, but actually it is still not enough, it still allows non-black(gray gradient). What I want is

Suppose I ended up having this image: a perfectly round circle done via `ellipse tool` and `stroke path`

![enter image description here][1]


Then I want to make sure `if a pixel is not white then make it black`. So what I want should be like this:

![enter image description here][2]

I ended up learning the use of `sharpen` but it still not works, it just make the gray more black PLUS it adds more feather so even sharpen fails me to accomplish this.

Hope somebody can help and guide me how to do this. Thanks~

  [1]: https://i.sstatic.net/H8llq.png
  [2]: https://i.sstatic.net/L6mHt.png