I can't work out what's causing this, but it's consistent. I create a nice wallpaper on my Mac which is a simple colour gradient. On Mac it looks smooth. I want it on iPhone too, but whenever I add it to Photos, the gradient now has bad banding. I've tried transferring the file by both adding to Photos on my Mac and letting it sync with Photos on iPhone, and also saving the .png file, then on my iPhone going into the Files app, locating it and then saving to Photos. The end result is the same. Can anyone help?