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File size saving for web
I noticed irfanview creates way smaller files when batch reducing & did
a little test with some different programs. The most obvious thing is
that saving with photoshop preserves the exif info and thumbnail adding
about 13KB to the file size unless you use the save for web route.
All these were done at mid range quality 50% for the same 640x425 image.
In order of file size:
60KB Photoshop saveas
47KB Photoshop saveas after stripping EXIF info with exifer
37KB Photoshop save-for-web
35KB ThumbsPlus 1:1 sub-sampling
26KB ThumbsPlus 2:2 sub-sampling
24KB ThumbsPlus 4:2 sub-sampling
That's a huge spread!
I didn't try the ThumbsPlus smoothing, I assume that's the same as
photoshop save-for-web blur which reduces file size.
Irfanview cut one pixel off in the resize producing 640x425 (not 426).
Photoshop save-for-web is nice because you see the before-after & it
helps to zoom in to 400% to see the effect. When I scrolled through
these samples I could only tell the irfanview file was missing fine
detail, normally large simple areas like the sky get posterized & that's
the ugliest effect, in those cases it's probably a small file anyways
since it's simple so you can use a higher quality.
I normally use about 60% to 70% & shoot for well under 100KB for a
640x425 image but now I'm going to have to remember never to use
photoshop without the save-for-web thing & use a higher setting if I'm
batching with Irfanview.
Most web designers try to make web general page images no more than 20KB
& that's almost the size of the EXIF info alone so I would definitely
think twice about including that. There are programs for exporting EXIF
into a text file & it would be worth taking such an approach in
designing a web site for photography.
I understand photographers are going to want a nice big picture so 20KB
is asking a lot but I've seen some awesome portfolios with tiny 300pixel
wide images that look spectacular so it's good to just remember that
it's not always necessary to make big files. People lose patience
quickly waiting for images to load, even a mediocre DSL line takes a
while to load a 120KB image when half that size would probably do.
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