On Sat, Jan 22, 2011 at 11:15 AM, Ralph Zerbonia
> My question is whether or not anyone knows of any image disadvantages, is
> there anything about LZW that would allow a loss of any visual fidelity?
LZW is indeed lossless. I just did a quick test to be sure that
GIMP's implementation is lossless and it turned out OK.
PNG is a lossless format as well, and may give a slightly smaller file
size than TIFF.
 I did the following in GIMP 2.6.10:
- Open an uncompressed TIFF file
- Save a copy with LZW
- Close all files
- Open original
- Open As Layers LZW copy
- Change LZW layer mode to "Difference"
- Move the cursor about in the image while looking in the 'Pointer' dialog
- All RGB values are 0% (black) throughout the image
(could also flatten the image at this point and use levels or curves
to verify that there are no anomalies)
 In an older version of Photoshop (5? 6?) I did the above and came
out with a very slight "shift" or "loss". It could have been a
mistake on my part, but at the time we figured it was a bug in Adobe's
LZW handling. I can't reproduce this any more in Photoshop - so
whether or not it was pilot error or a bug, it's no longer relevant -
except it's the reason I remember the above procedure ;)
Gimp-user mailing list