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RE: filmscanners: File format

I must admit that when I wrote my comments below I was only considering
files openened and saved as .jpg files from within editing applications like
Photoshop and did not take into account files saved to .jpg files
automatically by such devices as cameras.  Just speculating; but wouldn't
opening the camera created .jpg in an image editing program allow one to
determine the compression level of that file via one of the dialog boxes;
but that evidently is not the case.  Thus, the only suggestion that I would
have is if your camera saves automatically to .jpg and does not let you
select a compression level then the manufacture should be able to tell you
the default compression leve that the camera uses.

However, your point is well taken.
-----Original Message-----
From: owner-filmscanners@halftone.co.uk
[mailto:owner-filmscanners@halftone.co.uk]On Behalf Of Derek Clarke
Sent: Tuesday, April 03, 2001 12:04 PM
To: filmscanners@halftone.co.uk
Cc: derek_c@cix.co.uk
Subject: RE: filmscanners: File format

The difficult part is re-saving the file with the same compression ratio
as it had originally.

Even the mighty Photoshop just uses one compression ratio for all JPEG
file saves. That compression ratio can be set manually , but how do you
ensure it is exactly the same as the original ratio, especially if the
camera saved it originally?

To me, that is the main reason why it is sensible to store a picture you
intend to do anything with in an uncompressed format, irrespective of
whether the original file was a JPEG or not.

laurie@advancenet.net (Laurie Solomon) wrote:

> >Each time there would be some generational loss.
> Not necessarily true. If you open and close ( or resave) the compressed
> file
> without changing the compression from one quality level to another in
> the
> case of .jog or without resampling the image prior to closing or
> resaving
> the file, there will be no more degradation than opening and closing or
> resaving a raw uncompressed file.
> When you open a compressed file you have uncompressed it, so resaving it
> with the same compression as before or without engaging in any
> resampling
> prior to resaving the file  should not result in any additional losses
> in
> data or quality.
> -----Original Message-----
> From: owner-filmscanners@halftone.co.uk
> [mailto:owner-filmscanners@halftone.co.uk]On Behalf Of Larry Berman
> Sent: Thursday, March 29, 2001 8:31 PM
> To: filmscanners@halftone.co.uk
> Subject: Re: filmscanners: File format
> What would be the point of storing and reopening and saving the same
> image
> in a compressed format repeatedly. Each time there would be some
> generational loss. Store in an uncompressed native format to your
> graphics
> program. If you open a jpeg in Photoshop it automatically takes on the
> characteristics of a PSD. That's why you should save it as a PSD prior
> to
> working on it. Then use Photoshop's "Save for the Web" to create your
> compressed jpeg.


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