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| jamthomas | Senior Heliman - Location: Newberg, Oregon - |
I didn't write this but I thought it was informative for those who are interested.
Jim
As far as Jpeg's becoming TIFF, that's not exactly what happens, but it's
essentially the same. When you open a Jpeg into photoshop, it "expands" to
it's uncompressed size. If you do a few changes and save it back as a Jpeg,
you will subject it to another round of jpeg compression. If you save it as
a TIFF, then the degradation stops there. However this does not mean that
if you subsequently save the resulting TIF as a Jpeg that it would be any
different that having first saved it as a Jpeg.
For those that are "geekified" and want to know more about the current Jpeg
standard, see (http://www.ece.purdue.edu/~ace/jpeg-tut/jpegtut1.html) for a
good explanation.
That's why I always maintain a "set" of versions for each image. There is a
high res "master", an "access" image saved as a TIFF, and the same
converted to sRGB and saved as a standard Jpeg. How these are maintained
and created is all part of the Image Database section of Controlled
Vocabulary (http://www.ControlledVocabulary.com/imagedatabases/) for those
that are interested.
The advantage of keeping a TIFF of the downsampled file is that I don't
have to go back and downsample all the master files again when the Jpeg2000
standard becomes prevalent. Plug-ins are available now for both Photoshop,
Netscape and MSIE, but it's not built in to the current versions. When that
comes to pass, that's where I'm headed. Jp2 (jpeg2000) has a built in
"lossless" format that reduced the file size by approximately half. If you
do compress it's based on wavelets (not the earlier discrete cosine
transform compression) . JP2, as well as the earlier Jpeg format, are true
open standards. Like it or not, Adobe actually holds the patent on the TIFF
format, so it's stability as a format is not a given. Though if past
performance is any indicator of future performance, it's still a good
choice for a storage format.
HTH,
David
David Riecks
http://www.riecks.com, Chicago Midwest ASMP member
http://zillionbucks.com "The Webhost for your Creative Business"
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Creating an image database? be sure to visit
(http://ControlledVocabulary.com/)! |
| 06-23-2003 Over year old. | | | |
