Although I love OfficeLens, it does not yet do Black and White. CamScanner, however, does. While it is not completely black and white, you can use e.g. Paint.Net to do a magic wand selection on the “white” area, delete that selection, and use the PaintBucket to fill in the transparent area with white:
One thing I do not like about CamScanner is that if I want to upload to OneNote, it requires access to my Contacts, amongst others. I declined that, and instead saved to PDF.
Actually CamScanner in what they call Magic mode is great, and there is an option to mail it as a jpg. So apart from rotating in Paint.Net, this is exactly as I took it using CamScanner on my Lumia 735:
and here. At the edges, you can see the brown of my desk. So it has done a great job doing the right thing with the white and the black. I therefore reluctantly am of the opinion that CS is better than OL.
Some more scribbles: