On Fri, 31 Aug 2007 12:24:47 -0400, Robert L Krawitz <[EMAIL PROTECTED]> wrote:
> It sounds like what's happening is something like this:
>     1) Current JPEG quality setting is 85
>     2) User selects "Use quality settings from original image if
>        original image is better"
>     3) Original image has quality setting of 98
>     4) User saves image
>     5) Now the current JPEG quality setting is changed to 98
> Is that correct?

Almost.  Step 2 currently happens automatically if the quality of the
original image is better than the defaults (because of the complaints
that gimp was destroying the quality of some images without warning).
But this may change, so step 2 could again require an explicit action
from the user.

> If so, then (5) seems wrong to me.  [...]

Yes, this is exactly what I tried to explain in my previous messages.
The problem is that the JPEG plug-in and most other file plug-ins will
automatically re-use all settings from the last file that was saved.

> My own preference is to err on the side of caution; I'd rather make a
> mistake of saving at too high of a quality (which loses less
> information) than too low.  If I accidentally save a thumbnail at
> quality 98 or 100, all I've done is wasted a little disk space; if I
> save a good image at 85, I've lost a lot of data.

And this is what is currently implemented: if the quality level of the
original image is higher than the current default value, then the
quality from the original image will be selected automatically.  But
since the JPEG plug-in shares the same behavior as the other file
plug-ins, this new value is automatically remembered for the next time
you save an image.

The combination of these two things (using the original quality if it
is higher, and the automatic re-use of the last values instead of
using the defaults) causes the problem reported by Jakub: if you load
and then re-save many images that were saved at different quality
levels, you end up with the last image saved at the highest quality
level (maximum value from all images), which may be much higher than
the default value or than the original quality of that image.

This is a bug that should be fixed.  But after discussing this
briefly with Simon in #gimp, I think that it would be better to
postpone the real fix to GIMP 2.6 because it would not be possible to
fix all (or even most) file plug-ins for 2.4.  And if only the JPEG
plug-in (and maybe PNG) behaves differently than other plug-ins, then
some users will probably complain or at least be confused.  It may be
better to postpone the real fix until all plug-ins support a way to
load and save defaults, and maybe support multiple presets.

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