exporting a UV face layout that is not square?

Hi , i have unwrapped a mesh while i had an image in the uv editor that is not square.

its 512-256

but everytime i export the only option i get in the size box is to write only one dimension for example 1024.

but not the second one , so it stretches my layout.

any ideas ?

I think this can be avoided you just place all your UVs on the top/bottom half of a full square and export that. You cut off the useless half and when you load it in Blender, you’ll only have to scale up the UVs in one axis by two (with s, y, 2, that’s pretty easy).