Gradient used to mimic neutral density filter along horizon

[gstalnaker]

(12-28-2018, 07:04 AM)Ofnuts Wrote: Looking at your picture, i think the right way to do it is to use  luminosity mask.

Thanks ofnuts -- while such a masking technique may be useful for this particular image, what I was after was a technique that allowed me to use the regular gradient tool.

I suspect, given that neither you nor rich2005 know of such a thing and given your combined expertise in GIMP, that this is not an easy thing to do.