[youngtaff]

The ideal of an image format the can progessively support different sizes was discussed back when solutions to the responsive image issue were first being sought out e.g. https://blog.yoav.ws/posts/responsive_image_container/

JPEG 2000 already offers the ability to encoded multiple sizes of an image in the same file https://www.verypdf.com/pdfinfoeditor/jpeg-jpeg-2000-compari...

I think there was some hope that JPEG XL might be able to meet this need too