Quote:...[I thought it might be possible to decompose the problem image into colour layers in GIMP, move the pixels of one layer over slightly, and recombine the layers. I don't know exactly which colour is out of sync or how much to move them so it is an experiment....]
I will throw this old script into the hat. One of Saul Goodes scripts, shows how you can combine those grey masks back into one. Each layer and mask move as-one, just use the move tool on the layer. Note the layer mode for RGB additive colours. The script can also decompose to CMY for a subtractive model.
You can of course make similar up manually, copy and paste the decomposed image layers into layer masks.
This is the original for Gimp 2.8 (there is a modified version for 2.10) Unzip, put into (probably) /Users/MyName/Library/Application Support/Gimp/2.8/scripts Registers in the layers menu.