04-21-2022, 07:38 AM
(This post was last modified: 04-21-2022, 07:43 AM by rich2005.
Edit Reason: typo
)
Clever old PS 
never seen that one before
Using Gimp a bit more hands on. First thoughts, a couple of ways
Make a gradient using the FG / BG gradient. Once selected those colours appear as a 'custom gradient' top of the gradients dock
A right click in the Palettes Dock and import a new palette using that gradient as a source.
Map > Set Colormap using that new palette.
https://i.imgur.com/NR9NzuY.mp4
or for a quick-n-dirty way using indexed images inherit the colormap of the original image
Make a new blank image
Fill it with a gradient
Convert to indexed.
Click and drag the original image over as a new layer.
https://i.imgur.com/yRLrGTy.mp4
Note the various modes for gradients, it does make a difference for colour distribution.
never seen that one before Using Gimp a bit more hands on. First thoughts, a couple of ways
Make a gradient using the FG / BG gradient. Once selected those colours appear as a 'custom gradient' top of the gradients dock
A right click in the Palettes Dock and import a new palette using that gradient as a source.
Map > Set Colormap using that new palette.
https://i.imgur.com/NR9NzuY.mp4
or for a quick-n-dirty way using indexed images inherit the colormap of the original image
Make a new blank image
Fill it with a gradient
Convert to indexed.
Click and drag the original image over as a new layer.
https://i.imgur.com/yRLrGTy.mp4
Note the various modes for gradients, it does make a difference for colour distribution.