The noir style is achieved by converting the original picture to greyscale and then increasing contrast and brightness as necessary. This can be done in open source photography workflow application and raw developer Darktable.
What is noir portrait photography style about?
The purpose of noir portrait photography is a more dark, intense and sinister tone to the picture, so it resembles, how it would look, if it was taken in the 30’s.
My noir styled portrait.
More about noir portraits and photography developing.
How to import, export and remove film rolls and pictures in Darktable by myself. The official website of Darktable. Film Noir Portrait Shoot by Gavin Hoey.