Duplicate the base layer again, move it to the top and set blending mode to “Lighten only”.
A side-effect of this lame tone mapping technique is that high radius halos mighty appear, and the sky could be darkened in a cheesy way. You would more easily notice halos in what should be an even blue sky than in grass or rocks. As we only want to make the shadows pop and we don’t want a fake “HDR look” cheesy sky, we fix it in this step. This layer’s job is to undo the effects of this whole technique in the light areas.
Desaturating in step 2 can be done in numerous ways:
You could just desaturate it as I did, but there already you have 4 methods to choose from (in GIMP 2.9.4).
You could use the Mono Mixer, enabling “Preserve luminosity” and sliding the “Red Channel Multiplier” all the way to the right.
You could decompose the image to RGB (or other) and use one of the resulting layers.
Note: Decomposing to RGB and using the R channel leads to an almost identical result as you’d get using the Mono Mixer as described in the previous step - a workaround if you’re stuck with GIMP 2.8.
Compare the first and last screenshots. The end result is a photo with a little bit more pop without looking fake. Lower the blur radius and try other desaturation methods for more cheese.
I will say, even if you have directed this tutorial to beginners, it is the nice way to show every user what can be achieved with GIMP blending modes. Description for them can be found on the GIMP help page and elsewhere but their true performance can only be shown with such examples.
I wish if we had an extra page for such tutorials.
Sometimes I find useful to replace the gaussian blur with some other edge-aware blurring method (like the bilateral filter) to reduce the presence of halos…
Anyhow, just for fun I created a PhotoFlow preset for this technique. All the steps you describe are applied non-destructively, allowing for example to tweak the blur layer while looking at the final result in the preview.
If anyone is interested, the preset file is here.
No merci David mais c’est dans Photoflow, il y a un filtre special tone-maping et je demande à Carmelo comment utiliser son fichier preset special dans Photoflow. Merci encore David pour ta gentillesse.