seniors moment... don't worry, it will pass...

Thank You Wallace

Sure thing Pirate541.

Good stuff - you can also apply the Gaussian blur on the X or Y axis only - play around with it to see what gives you the best results...

Good point pauls46. That kind of blur hadn't occurred to me.

Invert of a grain merge is the same as doing a grain extract, so it is a kind of unsharp mask. When radius is small (<8) it is a typical sharpening, when radius is high (>30), it is doing local contrast enhancement (fog removing). 15 is something in between. The amount in unsharp mask menu is like opacity applying to your newly created layer.

The technique I demonstrated does not involve inversion of grain merge. Only the color is inverted and the blur radius used depends on the size of the image.

I recently stumbled upon a PS/Topaz tutorial for sharpening a noisy image without sharpening the noise: https://www.youtube.com/watch?v=p2aln2dLKdw

The GIMP equivalent is to take the gray layer we've been talking about, and run a noise reduction filter on it. I use G'MIC's Ian's Fast Denoise and it works like a charm!

Thanks for the tip and the link Acmespace. I'll definitely check that out.

Pat talk about inverse/blur in http://gimpchat.com/viewtopic.php?f=23&t=6553&hilit=freaky+detail

I see what you're getting at and find it very interesting. I'm not a big user of G'MIC so I also didn't know that G'MIC provides a filter of this type.
Thanks okyl168.