i’m trying to fix a panoramic stitched together by a number of different pictures. Please see below.
I’ve used the Perspective tool to help this picture a lot already (believe it or not) but the picture has an obvious bow to it which the Perspective tool doesn’t help. I’m a fair Gimp user but I’m not sure how to address this problem. Any thoughts on what I can use here?
I’m not a regular GIMP user, so I’m not sure what you could use there…
I wonder what software you used to stitch the image? Most stitching software has the option to use the ‘perspective’ projection which usually avoids this kind of curvature.
using hugin as stitcher will let you choose a different projection - e.g. cylindrical - that may help you.
Wow…way cool!
It looks like Mathmap Defish is not supported well anymore and that gmic is preferred…thoughts?
If G’MIC had a defish option, it would be much easier to use, but I checked and didn’t find one within my GIMP G’MIC filter. Maybe someone can share a defish preset with folk (to include me) with options to also address inner distortions (which I didn’t do with the result posted earlier). 
I have taken panoramas like this where no software can prevent the bending. It is when you have to stand relatively close to a wall an do a series of shots . I am impress with the Mathmap Defish, but the ends of the image are very soft.
I haven’t got time to try it at the moment, but I wonder if the warp tool (correct name?) in GIMP could be used to bend the image back into shape. Another tool could be the filter used to fix barrel distortion. Just ideas. I might find time later to try something.
If its a wall like this, move parallel to it and try and keep the camera sensor square to the wall. Walk along and take photos that overlap one another. Then you won’t have the warping or the softness.
I agree with your recommendation here Mica for the occasions when that is possible. I have done that in the past
With a good enough quality original it can be achieved using the cage deform tool. Pretty easy once I gave it a try. However, this image is probably not up to being fixed, but it can be done. My bad that I accidently cropped the end figures off. I must have been zoomed in too far.
If you intentionally want to take a panoramic photo like this, then you should take some photos mainly vertically and parallel to the subject as @paperdigits recommend, this is a good way to prevent the fisheye effect when stitching the photos together with any software. I use Xpano and I used to use Hugin, amazing applications with many options to correct distortions.
In this photo I had to take almost four shots parallel to all those people. It was challenging to do that 
This is a congregation of Spanish descendants from Zamora in Cuba.
Greetings from Havana, Cuba.
Maybe try G’MIC, Deformations > Distort Lens
In Deformations there are other filters like Warp [Interactive] to manually do it as well, it needs attention on the dots, though)
Windows BAT script, using ImageMagick:
magick ^
C:\web\im\bowed.jpeg ^
-fx "dx=i/w-0.5; dy=j/h-0.5; ang=abs(dx*pi/1.7); dydash=(dy*cos(ang)+0.5)*h; p{i,dydash}" ^
-quality 40 x.jpg
The lines at the top are roughly straight. Increase 1.7 to about 2.2 to get the lines at the bottom roughly straight. So a blend of the two might straighten them all.
EDIT: Uploading now works, so here is a small version of x.jpg:
Here > Flattening a scanned book
Download the script, then in GIMP, make 2 paths, run the script
result:
