I doubt the 100x range, too, but Photoshop is decades old and, likely, has lots of its filters written in assembly for speed, with zillions of variants for all kinds of sometimes long gone CPUs and GPUs. It also still may have its own memory manager.

It that is true, it should be possible to get large wins in LOC if one either is willing to give up orders of magnitude in speed and memory usage, or is equipped with a sufficiently advanced compiler.

There likely also is some room for improvement if one is willing to change the file format (.psd is not known for its consistency), but that would likely be a rounding error.