Image data is just binary blobs. You aren't splitting that into channel columns or anything. But an image file for an editor like Gimp isn't one image blob. It's dozens or hundreds of them - one or more per layer - along with tons of associated metadata at every level.
All that tends to fit sensible schemas and managing it is what SQLite shines at.
All that tends to fit sensible schemas and managing it is what SQLite shines at.