Nice of you to say Pascale :) I was only passing on information which I have learned along the way - it is not my method but one from a book. I am glad you have found it useful, that makes posting it worthwhile. Only things I can add are remember you can always adjust the background layer too, if you do your b/w adjustment on another layer. There are so many different settings to try it would take a life time to get to them all. For this image if you wanted to lighten the foliage you could use R40 G100 B-40

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html