----- Original Message -----
From: "David Dyer-Bennet"
: On the other hand, I *want* the metadata preserved in web images. To
: my mind, stripping metadata is like deliberately erasing what somebody
: earlier wrote on the back of a photo.
I agree about exif info, but the 'other stuff' is of concern, stuff
that is
not 1k or 2k of text, but neither is it 'image'.. it seems to be
something
else - profiles maybe? Monitor/printer information? I don't know..
Just did a little test
I dragged a noisy, busy nocturnal street scene off my memory card,
copied
it a number of times and began running it through a few programs to
resize
and save it, here's what I found.
Original Image from the 6 Mp camera pixel dimension 2560x1940 = 1.81Mb
target size = 800x600 (preserving proportions)
I then 'stripped' the original image to see what quantity of
(arguably ;)
superfluous data was present - 3.6Kb was stripped.
I then restored this image to it's prestripped state (jstrip backs up if
you ask it to) and proceeded on.
I resized using lanczos filter in irfanview and save at 80% quality
to get
an file size of 52Kb.
(irfanview has lanczos,hermite,triangle,mitchell,bell and b-spline
filters
for resampling by default, others can be added)
I resized the stripped version also and got an image size of 48.4Kb
I stripped the unstripped, resized version above and similarly got an
image
size of 48.4Kb
NOTE, Irfanview kept the EXIF information on downsizing and saving
(prior
to stripping by jstrip).
I then used photoshop 5.5 to open and resize as above, the unstripped
original image, saving at quality '8' to get a file size of 78.3k.
(PS has bicubic, bilinear and nearest neighbour interpolation)
I then 'stripped' this image (NOTE: the EXIF data *WAS NOT* preserved in
the resize & save process) and removed 6.2Kb of something other than
exif.
I then used photoshop 5.5 to open and resize as above, the unstripped
image, 'saving for web' at 80% quality to get a file size of 1.37Mb.
err, retrying that at 60% quality I get a file size of 71.6Kb
I then 'stripped' this image (NOTE: the EXIF data *WAS NOT* preserved in
the resize & save process) and removed 59 bytes.
This exercise left me with a few questions:
Why did PS *not* retain the exif data on resizing and saving?
(Irfanview gives me the option when saving to include or exclude this
information)
What did it put in it's place?
Why was I stripping a *lot* less data from my images than I've seen
in some
other web images I've downloaded and stripped?
why is Photoshop making such large files - the 60% 'save for web' image
(71.6Kb) was visibly softer and showed more artifacts than
Irfanview's 80%
quality 48.4Kb file?
I know Irfanview outperfoms PS according to many independent tests for
quality, but that's a dramatic fifference..
less answers, more questions ..
k
