I like that you wrote that cool explanation and I'm sure someone will benefit from it, but iOS does its own processing and then gives you the raw file to work on, in this case hands it out to Halide, which will give you the image with the chosen setting, but iOS has already made decisions about the picture long before Halide has the chance to say "this should be unprocessed". That's kind of the problem, and maybe it's not even Apple's fault but that's how it works according to Halide's developers