The encoder option -Q<quality> (that's a capital Q, lowercase -q is used to decode a lower quality preview by only reading part of the file) can be used to do lossy encoding, where -Q100 is lossless and -Q0 is usually the most lossy you would want to go. But you can go lower if you want, using a negative number (e.g. -Q-50); there is not really any lower bound.
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The encoder option -Q<quality> (that's a capital Q, lowercase -q is used to decode a lower quality preview by only reading part of the file) can be used to do lossy encoding, where -Q100 is lossless and -Q0 is usually the most lossy you would want to go. But you can go lower if you want, using a negative number (e.g. -Q-50); there is not really any lower bound.