Raw-file to Black and white photo in Darktable

Ok, here comes a little tuto on how I do my BW conversions:

First of all, I shoot RAW, always!
Then my OS is Ubuntu (15.04) so I don't have Lightroom or Photoshop, so my weapons of choice are Shotwell to import the RAW files from my camera, Darktable for processing of the RAW files and finally The Gimp for anything that goes behind RAW processing. All three are included in the Ubuntu distro and free.

First I open the Raw file in Darktable:

Darktable automatically does some pre-processing, sharpening and applying the Base Curve. Sharpening is ok, but the Base Curve is modifying the image in a way you might like or not (I don't!). My guess is, that this option is supposed to make it look like the preview on your camera screen.

So let us de-activate the Base Curve!

The image immediately becomes less vibrant, but don't panic, that's ok for the moment, we'll change that!

For the moment we go to the Levels module.
When de-activating the Base Curve you may find that the histogram shows empty spaces on the bright (right) side or the dark (left) side or both. You can either double click on the Auto button or adjust it manually by dragging the dark and/or the light triangle to the beginning/end of the histogram curve.

Next step, we adjust the Tone Curve:

I always start with the dark (lower) part, just click on the bright line and drag it down a bit to give more punch to the blacks, but keep the part behind the anchor still in a curve.

Now to the bright (upper) part, as you see, I set the anchor point farther away from the top and the "almost flat" part in front of the anchor is longer than the dark part.
This brightens a bit the midtones and makes the clouds "pop", but be careful not to burn out the whites!
Depending on the image you may want/have to add more anchor points in the middle part of the curve, but here it looks good to me with the "simple" S curve.

I crank up a bit the Saturation,

add some Vibrancy

and Clarity in the Equalizer module by either using the Clarity preset or adjusting the Edges curve manually.

Next step the Monochrome module! Adjust the circle with your mouse wheel to include only four squares

and drag it a bit around the center to see what happens (you get realtime update) without getting too close to the borders, which can give a dull outcome. I prefered these settings.

Finally, a bit of cropping (or not). Again that depends the image and your taste!

And off we go to export our bw photo!

And here is the final result: