RE: filmscanners: File format

[derek_c@cix.co.uk (Derek Clarke)]

That wouldn't help as different programs use different scales in their 
Options or Save As boxes to determine JPEG compression levels, there 
doesn't seem to be a standard.

Also as other people in this thread have pointed out, even repeatedly 
saving the file at the same compression level in the same program can lose 
stuff...

laurie@advancenet.net (Laurie Solomon) wrote:

> 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.
> >
> 
>