Usage on retrofit partition files?

It would be great if you could use this program on files like super_system.img, super_vendor.img and super_product.img and not just on a device. Currently converting those sparse files into raw files (simg2img), setting up a loop device (sudo losetup -r /dev/loop1 super_system.raw.img; sudo losetup -r /dev/loop2 super_vendor.raw.img; sudo losetup -r /dev/loop3 super_product.raw.img) but I don't think you can use the program on that.

$ sudo ./make-dynpart-mappings /dev/loop1 0
system_a: Unresolved block device, punching hole
vendor_a: Unresolved block device, punching hole
odm_a: Unresolved block device, punching hole
product_a: Unresolved block device, punching hole
product_a: Unresolved block device, punching hole
system_ext_a: Unresolved block device, punching hole

Afterwards I have the "partitions" in /dev/mapper/ but they're unusable (things like Buffer I/O error on dev dm-1, logical block 284768, async page read)