Jpeg works by saving closely matched colors as say color 003, 120 pixels (or
something like that). Now when you open the image again all those pixels are
filled in with color 003. If the next adjacent 80 pixels are say color 005 they
are now the closest matched and jpeg saves both of them as 200pixels of color
004. After a lot of resaves you wind up with only a few colors in the image.
Note that it does this every time you do a save, even the first time although
it is not very noticeable the first few times it does happen. Please note it
does that when saved from an open file, copying the jpeg changes nothing
It is the nature of the beast. Jpeg is really only intended for saving the
final distribution image. If the jpeg out of the camera is the final
distribution image as in most snapshots then jpeg is fine.
graywolf
http://www.graywolfphoto.com
"Idiot Proof" <==> "Expert Proof"
-----------------------------------
mike wilson wrote:
From: "Shel Belinkoff" <[EMAIL PROTECTED]>
Date: 2005/06/14 Tue PM 02:00:21 GMT
To: [email protected]
Subject: Re: RAW v JPEG
Each save was made at the highest resolution and least compression possible.
Shel
In which case, there is no sensible logic to it. If you tell the programme to
save the file at the biggest possible size, the logical thing, to me, would be
for it to save everything. If it proceeds to chuck away information after
getting that instruction, it is not a clever file format for photographic use.
[Original Message]
From: mike wilson
Shel Belinkoff wrote:
Well, I didn't change a thing, just opened and saved the file. I just
did
it again to be sure and every time the file was saved there was a loss
of
the number of "unique" colors and the file size changed:
http://home.earthlink.net/~pdml-pics/jpgloss.jpg
Shel
Unless you choose the biggest file size option for the resave, my
understanding is that jpeg will always chuck away what _it_ thinks is
uneccessary.
mike
[Original Message]
From: Rob Studdert
I have no doubt about the validity of your observations however if a jpg
image
hasn't been transformed in any way it should be saved without loss of
colour/detail. A transformation could also take the form of rendering an
image
to an alternate colour space.
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