Set macOS wallpaper without re-encoding image

I have a PNG gradient with the same resolution as my screen, 3072 × 1920, and 16-bit color, which renders without banding when viewed full-screen using Preview, but becomes banded when set as the desktop wallpaper. How can I prevent whatever re-encoding is doing this? I’ve tried exporting the wallpaper as an 8-bit PNG, but that introduces banding even when viewed in Preview. I’ve also tried the sRBG, Display P3, and Color LCD color profiles, and using a TIFF, as well as setting the wallpaper via System Settings, the Finder context menu, and an AppleScript that tells Finder set desktop picture to POSIX file "/example/filename.png".