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Howto: Use resynthesizer for GIMP on OSX
Resynthesizer is a great plugin that can create textures based on an arbitrary input.
Here's a photo I took, and the angle of the sun meant I got my own shadow in it.
Using resynthesizer I can quickly create some new texture there to replace the shadowed area.
The plugin is included with the OSX version of GIMP from gimp.lisanet.de (thank you!). For windows and linux you need to download it from www.logarithmic.net/pfh/resynthesizer.
Here's what I did.
For me it seems that the plugin doesn't work if you have selected the background.
So I selected an area to be the texture source and pasted that as a new layer, its called clipboard.
Then I selected a part of the background and pasted into a new layer. Its called clipboard#1.
You'll see that GIMP places the copied image right at the top of the picture. So drag it back down to align with the background.
Then with the layer clipboard#1 selected, use the lassoo tool to select the area to be resynthesized.
Then from filters>map select resynthesize
In the dialog, deselect "Make horizontally tileable" and "Make vertically tileable" and in the "Texture source" box make sure you select the layer with the sampled texture. You can check by seeing the thumbnail preview.
Click OK, and the plugin does its work.
And here's the result. I've left the marching ants so you can see the old and the new.
and here's it without the marching ants.
You may need to play around with the exact source texture area, and on the 'Tweaks' tab there are some settings to fine tune what the plugin does.