stimmt ich habe avif falsch charakterisiert, aber finde ist trotzdem nicht ganz inkorrekt

With AVIF, progressions work more like frames of a video. You provide up to four frames, so that’s three phases before the final image. Again, like a video, each frame can use data from the previous frame as an optimisation. An advantage of this is you can choose exactly how those frames look. In the example above, I went with a single preview frame: a 1/8th resolution version, with a bit of blurring. But, your preview frames can be completely different images if you really want.