>That's right in theory, but I'm not so sure that's what happens in
practice,
Lynn, you are right that the way any given application implements a
compression program (be it .jpg or some other compression program) will
often effect what happens in terms of files sizes, production of artifacts,
and even cross application or plateform portability.
>I've never actually *seen* any differences or degradation, but if the
>numbers aren't the same from one save to another, something must be
>happening.
I think you explained some of it yourself when you said:"E.g. Photoshop will
add about 5-20KB to a saved file from another program, and this I know. It's
probably just embedded Photoshop stuff, but it increases the file size."
-----Original Message-----
From: owner-filmscanners@halftone.co.uk
[mailto:owner-filmscanners@halftone.co.uk]On Behalf Of Lynn Allen
Sent: Friday, March 30, 2001 10:58 AM
To: filmscanners@halftone.co.uk
Subject: Re: filmscanners: File format
Tony wrote:
>If you merely open and save a JPEG at the same compression, without
editing, you lose nothing. If you edit, you lose information. It's
impossible to quantify how much, since it varies depending on the image and
what you do to it.
That's right in theory, but I'm not so sure that's what happens in practice,
IME. A program opens and re-adjusts the image for viewing; I've seen both PS
and PP8 change the size values on a subsequent Save. If you don't edit, then
don't Save or Save As unless you need to change formats. Just cancel it.
Then you *know* it's the same picture you loaded.
I've never actually *seen* any differences or degradation, but if the
numbers aren't the same from one save to another, something must be
happening. It probably isn't important, but it's there. E.g. Photoshop will
add about 5-20KB to a saved file from another program, and this I know. It's
probably just embedded Photoshop stuff, but it increases the file size.
If your file sizes aren't critical, then there's probably nothing to worry
about. Mine were, so I worried. :-)
Best regards--LRA
------Original Message------
From: TonySleep@halftone.co.uk (Tony Sleep)
To: filmscanners@halftone.co.uk
Sent: March 30, 2001 1:40:00 PM GMT
Subject: Re: filmscanners: File format
On Fri, 30 Mar 2001 09:49:05 +0800 httin (httin@china.com) wrote:
>
> Did any one knows whether is there any informations/details loses when
> store in compressed JPG format in maximum quality 10 and while you keep
> opening and saving the same file many times?
If you merely open and save a JPEG at the same compression, without editing,
you lose nothing. If you edit, you lose information. It's impossible to
quantify how much, since it varies depending on the image and what you do to
it.
> And how about the raw file TIFF?
Lossless, whatever you do, except for the distortions introduced by
arithmetic
during editing operations. Again, this is variable.
Regards
Tony Sleep
- Online portfolio & exhibit; + film scanner info
&
comparisons
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