I also learned a lot from the various JPEG articles on ImpulseAdventure (no affiliation), e.g.:
https://www.impulseadventure.com/photo/jpeg-quantization.htm...
https://www.impulseadventure.com/photo/jpeg-compression.html
https://www.impulseadventure.com/photo/chroma-subsampling.ht...
They also have a lot of practical stuff (which chroma subsampling will Photoshop actually use when you save at 80% quality?) in addition to the theory.
I also learned a lot from the various JPEG articles on ImpulseAdventure (no affiliation), e.g.:
https://www.impulseadventure.com/photo/jpeg-quantization.htm...
https://www.impulseadventure.com/photo/jpeg-compression.html
https://www.impulseadventure.com/photo/chroma-subsampling.ht...
They also have a lot of practical stuff (which chroma subsampling will Photoshop actually use when you save at 80% quality?) in addition to the theory.