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The DC coefficients in a progressive JPEG are literally an embedded thumbnail (a 1:64 copy of the original) right? Is the question if the second "layer" replace
by edflsafoiewq 22d ago
The DC coefficients in a progressive JPEG are literally an embedded thumbnail (a 1:64 copy of the original) right? Is the question if the second "layer" replaces the thumbnail or layers corrections on top of it? It wasn't clear to me which AVIF does.
- cpburns2009 21d agoAccording to this source [1], a second layer can progressively provide the rest of the image data: > Note: AVIF supports two types of progressive decoding. Spatial scalability can be used to offer a lower resolution image for network constrained users and 'progressively' provide a higher resolution image by sending just the additional data required to fill in the high frequency details. Quality scalability offers a similar progression by steadily improving visual quality with each render. That is totally not what I expected. Though it's not clear to me how exactly you achieve it. [1]: https://web.dev/articles/compress-images-avif https://web.dev/articles/compress-images-avif
- edflsafoiewq 21d agoAFAICT progressive AVIF is actually using the "spatial layers" feature of AV1, which was designed to embed multiple resolutions of a video in one bitstream. The limit on four spatial layers comes directly from AV1. The previously decoded layer/progressive-step becomes a reference frame that the next layer can draw from just like eg the temporally-previous frame can be referenced by interprediction.