Getting a round horizon straight

I created this using Arcsoft Panorama Maker; the original file is more than 8000 px wide.

Obviously; before cropping I'd like to have the horizon straightened.

ty

lol @ 8000 px wide.

If your PC can take it, (it should..)
flip your image 90 degrees CW or CCW,
select all, and apply the shear filter (it's in the distort menu).

You'll see when it looks straight.
I can't come up with a more decent or easy way of doing that. :confused:

EDIT: oh, and obviously, flip it back after the operation. :D