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Jpg is lossy and throws away information every time it is used, that’s why you get the “deep fried effect” when you re-encode something repeatedly. PNG is lossless so it’s a perfect replica of whatever image you encode with it. It does take up more space however.
Minor niggle: the ‘deep fried effect’ isn’t because jpg throws away information every time, it’s because the compression algorithm averages pixel boundaries, and that averaging multiplies with each compression pass.
It can actually bloat the size of the file by adding information – adding data to previously null pixels, whereas png would keep them clean.
e: it achieves this through pixel averaging (fuzzing), which is why you’ll see grey artefacts bleeding into the pixels around line art. This is magnified with each compression.
You’re conflating “data” with “information”.
Repeated re-encoding loses information. “The compression algorithm averages pixel boundaries” is a perfect example of losing information.
That it sometimes results in more bits of data is a separate phenomenon altogether.
Thank you I learned something today.
That’s fair. Thank you for making that distinction.
e: It’s still bad for the user, though.
There is lossless JPEG, but nobody uses it. And there are lossy PNG encoders, and some people use them.