Thank you for your kind comment.
The subs are 15s, 60s, 300s, and 600s.
I have stacked in DSS. I stacked 15s by themselves, and the 60s by themselves, and then combined the stacks in PS5.
I stacked the 300s and 600s together, and used Digital Development in Nebulosity.
I combined the 15s+60s-combined with the 300s+600s in PS5. I've used curves , labcolor mode the two separate layers, and a highpass filter on the flattened composite of the two layers.
But come to think of it: I know very little about serious image processing.
Hints, tricks of the trade, are welcomed!
