>The difficult part is re-saving the file with the same compression ratio as
it had originally.
>Even the mighty Photoshop just uses one compression ratio for all JPEG file
You can save at the same compression ratio, but that doesn't mean much. I
noticed this several months ago, when a CD photo album size that was under
control went radically *out* of control. All programs seem to differ.
You probably own more than one imaging program. Try this: note the file size
of a previously JPEGed file, and load it into your various programs, one at
a time. The file will probably show a different file size than the one you
wrote down, each time, and probably different than the last program that
loaded the file. I found that *every* program I have does this, to varying
degrees. It may depend on the program's interpretation of the PC graphics
card (so Mac users could see little or no difference, and our one Amiga/Mac
user will probably see none at all).
When your program saves this new image to JPG, it can't possibly be the
same, although the difference in appearance may not be significant. I found
a few cases where it *was* significant, however, with serious artifacting
and in a couple of cases, posterizing as well.
Larry Berman published an excellent comparison chart of compression schemes
a few months ago on this web site:
If you haven't checked it out, you really should.
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