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[filmscanners] RE: JPEG2000 > Paul



> From: Julian Robinson
>
> a) it matters WHERE the modified pixels are, and how they are distributed.
> If distributed in patterns these can be detectable much more
> easily than if
> diffuse.  This is where jpeg has a problem, with its visible
> jiggles around
> transitions. I understand from what you and Robert say that j2k puts the
> changes that occur with compression in a more widely spread
> manner, so they
> are not so visible.  My own experiment on 10% files did not show much
> difference in overall quality betw jpeg and j2k - they were different in
> appearance, but not necessarily one better than the other. I need to try
> with other images when more time.
>
> b) contrary to your experience, when I looked at the histogram of the
> difference between original and compressed images, I saw  a bell curve of
> "difference pixels" differing from the original by around 4 levels, but
> also a 'tail' of lesser numbers of pixels differing by up to 30 levels
> (j2k) or 37 (jpeg) from the original.  There were not so many of them, but
> they would be much more visible.  Again it depends on how they are
> distributed as to how visible they are.

I didn't use a histogram, I just fished around in the difference with the
cursor. It wouldn't surprise me to see the occasional much larger value
right on a contrasty edge. But at 10:1, even magnifying the image, I still
haven't been able to see any degradation. Maybe I don't know what to look
for in JPEG2000--I certainly know what to look for in regular JPEG.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@ix.netcom.com


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