Creating B&W images

[rich2005]

Quote:...When I use the eyedropper how can I tell I am picking the right black or the right white?...

That is your decision. All you can do is check the histogram before applying the level settings.

In this one my chosen point for white, looks ok, black however introduces a small bit of clipping. If really concerned then adjust the right slider and move over to include the start of the histogram. That was shown in Ofnuts first post.
You can also use the Histogram dock to get a real time display.



Which linux? I use Kubuntu 16.04 and a Gimp 2.9.9 portable (an appimage) Gimp 2.9 is a development version so I do keep the standard Gimp 2.8.22 as well.