Hi Hank,
Here's what I know (which isn't all that much)
PNG format is "lossless compression", supports alpha "channel" (for
transparency effects, like in TIFF files) and is palette based. Sort of a
GIF file on steroids, and without the Unisys patent (which has all but
killed off any "freeware" GIF applications). 24-bit PNG files will thus be
quite "fat" (file-size-wise) compared to JPEG. Unlike GIF, however, there is
no animation support.
JPEG format is "lossy compression", which means information is actually
discarded/lost to reduce file size. This can produce fairly serious
artifacting as a result of "over-compressing" an image. It also means that
images degrade through successive edit/save cycles. There is no transparency
support in the current widely supported JPEG standard.
So the short answer to your question would be that a PNG image would likely
be larger than the same JPG image, but no information will have been lost in
producing it. Use PNG if you need transparency effects for web use. There's
a HUGE fly in that ointment though. Last I checked, NONE of the browsers in
common use correctly support PNG transparency, even though most ALL image
editors handle the full PNG spec. I spent 4 hours trying to figure that out
one night, until I finally had an extra brain cell light off and found it
bug-reported all over the place.
Don't know squat about the new JPEG2000 standard, myself. Theoretically,
however, some of the new "wavelet" compression formats should produce quite
small files without the losses resulting with the current JPEG compression
format.
What would be almost ideal, IMHO, would be a format that fully supports
transparency/alpha channel use, has selectable compression (both lossy and
lossless) and compression amounts, palette support and animation support, as
well as gamma "triggers" to handle the different monitor types. Oh, and
probably some sort of robust copyright marking that doesn't effect the image
as seen on screen (all the current ones are easily defeated) or printed
unless used without permission. :-) I don't want much.
I'm sure others will think of lots of things I've missed.
---
Scott Gomez
-----Original Message-----
From: Hank [mailto:zuikosis@xxxxxxxxxxxxxx]
Sent: Sunday, September 30, 2001 23:01
To: olympus@xxxxxxxxxxxxxxx
Subject: [OM] PNG? was: Photo Editing for Dummies
Dear Acer and Garth, Olafo and others-
Is there any advantage to using PNG format over JPG ? Does it compress as
well?
Most web browser support PNG but does it do anything that JPG does not ?
-- Hank
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