I've used the G'Mic CLI Montage command for some years and love it. I wrote a tutorial a few years ago on how to use the command with Thunar Custom Actions.

But I've recently started using it again and the old command



no longer works. I found this command does work:



And as a bash command:



The older command would create a montage while giving each image similar dimensions, e.g.:



The new command, however, will make some images much smaller and other images larger, e.g.:



What can I modify or add to the new command to make each image in the montage share the same dimensions?

Usually depends on the type and mode
If your pictures are all different sizes and you pick align mode they will stay different sizes.
If you pick scale mode they will scale to the same size

Sometimes easier to get a layout up and running in Gimp then translate to the gmic command

This for 2 wide by 3 deep V(V(H(0,1),H(2,3))),H(4,5)) which equates to 'VVH0:1H2:3H4:5'

And what is the gimp default as a command, 3 wide x 2 deep H(H((V(0,1),V(2,3))),V(4,5)) is 'HHV0:1V2:3V4:5'

but the more groups the more obscure it becomes best of luck

A bit of experiment getting each tile the same size. No joy with that. I think this should scale to 400 wide but then montage takes over and fits in depending on landscape/portrait proportions anyway. However it does make a smaller image. For 2x3 layout



Gmic is a bit short of a general scaling filter (at least I can not find one) I would use ImageMagick in your bash file prior to gmic.