On Sat, Jan 22, 2011 at 11:15 AM, Ralph Zerbonia
<ra...@universecentral.com> wrote:
> 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[0] to be sure that
GIMP's implementation is lossless and it turned out OK[1].

PNG is a lossless format as well, and may give a slightly smaller file
size than TIFF.


[0] 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)

[1] 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

Reply via email to