07-22-2018, 10:58 AM
There are a few ways.
Standard Gimp 2.10
If fairly regular like your example. You might find that color pick foreground (FG) then background (BG) top then bottom near the edges and a new wider background with a FG to BG gradient works straight away.
If it does not then a layer mask filled with a gradient, black-to-white bi-linear with suitable offset 'feathers' in the layers.
screenshot: https://i.imgur.com/cjvj9CQ.jpg
Liquid rescale plugin.
See: https://www.gimp-forum.net/Thread-Liquid...27#pid8227 for the plugin files.
This lets the user draw keep and discard areas, then scales to a new size.
What the plugin looks like in action: https://i.imgur.com/6DPhSwQ.jpg
The result: https://i.imgur.com/mTDK0fL.jpg
Standard Gimp 2.10
If fairly regular like your example. You might find that color pick foreground (FG) then background (BG) top then bottom near the edges and a new wider background with a FG to BG gradient works straight away.
If it does not then a layer mask filled with a gradient, black-to-white bi-linear with suitable offset 'feathers' in the layers.
screenshot: https://i.imgur.com/cjvj9CQ.jpg
Liquid rescale plugin.
See: https://www.gimp-forum.net/Thread-Liquid...27#pid8227 for the plugin files.
This lets the user draw keep and discard areas, then scales to a new size.
What the plugin looks like in action: https://i.imgur.com/6DPhSwQ.jpg
The result: https://i.imgur.com/mTDK0fL.jpg