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


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