[Gimp-user] Masking for Contrast Control - Can this be done in Gimp?

[saulgoode at flashingtwelve.brickfilms.com]

Quoting paperaussie <paperaussie at gmx.net>:

>
> Can any experienced Gimp users tell me how the process described in Ron
> Bigelow's article can be reproduced in Gimp most efficiently?
>
> http://www.ronbigelow.com/articles/contrast/contrast.htm

The following link is to a short screen capture of how that might be  
done in GIMP I use a similar technique quite often when adjusting  
highlights and shadows. There is no sound but the video should be easy  
to follow (I apologize for the jumpy pointer; my optical mouse died  
and I had to use a trackball).

http://flashingtwelve.brickfilms.com/GIMP/Temp/masking.ogv (OGG Theora 2.7Mb)

1. Drag your original layer over to the Channels Dialog and drop it,  
creating a new channel.
2. Hide the channel by clicking on its "eyeball" icon.
3. Return to the Layers Dialog.
4. Duplicate your original layer and increase its gamma using the  
Levels filter.
5. Add a layermask to the duplicate layer, initializing it to the  
inverted channel produced by Step 1.
6. Add a bit of Gaussian blur to the layermask (optional).
7. Adjust the opacity of the duplicate layer to obtain desired result.

Step 4 is not necessary if you already have an "overexposed" version  
of the original layer (created from a HDR RAW file), as was the case  
in the tutorial you linked to.