Hi Ron,

The article referenced here suggests firstly that default modes should
be lossless. The answer to why they are not for popular J2K codecs
is that quality is somewhat better (particularly at reduced resolutions)
when viewing lossy compressed images using the irreversible options
rather than the reversible. On balance, then, it is probably still better
to have the irreversible path as the default one.

Regarding the problems created by going to JPEG downstream, this
certainly has nothing to do with JPEG2000 per-se. We have to remember
that JPEG is lossy, so it only takes some small tampering with the
parameters to produce two different JPEG results from the same lossless
original stored in different formats. Perhaps, the JPEG coder being
tested is coming up with quantization parameters differently, depending
on the source file and its associated metadata.

Cheers,

david


----- Original Message -----
From: "Ronald Murray" <rmur@...>
To: <kakadu_jpeg2000@yahoogroups.com>
Sent: Friday, May 04, 2007 3:37 AM
Subject: [kakadu_jpeg2000] Lossless Encoding Problems?


>A recent post to a library technology listserv appears to document some
>problems with lossless PEG 2000 encoding:
>
> http://dltj.org/2007/05/almost-lossless-jpeg2000/
>
> "For our sample greyscale images, we have not yet found a way to perform a
> lossless transformation to JPEG2000 when a downstream derivative is JPEG;
> there are perceptible differences between the JPEG created from the TIFF
> file versus the JPEG created from the losslessly compressed JPEG2000
> file."
>
> It's not clear in this recounting where and how the losses are being
> incurred. Can the tech-savvy readers of this listserv give us a hand in
> clarifying and addressing this issue.
>
> Thanks,
> Ron Murray
>
>
>
> For problems with your subscription in this group please email
> kakadu_jpeg2000-owner@yahoogroups.com.
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