Ian Boreham
Tue, 04 Apr 2000 23:42:14 -0700
At 06:21 AM 4/5/00 +0200, Marc Lehmann <[EMAIL PROTECTED]> wrote: >You got it wrong: saving a jpeg in ANY quality (higher or lower) causes loss >of quality. Saving in the same quality as the original image causes quality >loss depending on the selected quality. > >As I said, the only effect is a similar(!) file size, and that every save >would cause about the same amount of quality loss. >From my understanding of JPEG (which is not expert), I would have thought that although there might be a small loss of quality on subsequent cycles, due to rounding-type errors, there would not be anywhere near the same as the initial loss due to discarding high-order, low-coefficient data. Discarding this data is effectively setting the coefficients to zero, so you would be roughly discarding zero on subsequent cycles. >Jpeg is lossy, in whatever quality you save your files. If you save your >file in 75% percent, load it again, and cycle you will loose quality >_every_ time you save, not just the first time. Are you talking about compressing to 75% of the previous cycle's file size, perhaps? If not, then I'd be surprised to see a large loss each subsequent time. Has anyone tried cycling and differencing to see the effect? Ian