Stephen Shepherd writes:

>> Maybe I am being a bit vague here or just dumb but this is why I am a
little
confused. I know I do not want to save a .jpg over a .jpg but what seems to
happen is that once imported from the camera the .jpg file is in  a folder,
I then open the .jpg, I may want to change the saturation  so I do this
after which when I hit save I get the .jpg option box up in photoshop asking
if I want to save at 1 through to 12. <<


Hi Stephen, if the current file is saved with as JPG, hitting save again
will resave it as a JPG over the top of itself (just making the point clear
if it was not <g>).

The message box you see is there because Photoshop does not know which
quality setting the third party non Adobe JPG writer to used.


>> The file does not just save as it was, it came from the camera and once
opened in PS when you come to save it you need to specify your settings
unlike a file already in the PS .jpg which if you adjusted the saturation
and then saved it justs saves it. <<


Yes, If Adobe write the file - then they know what level of compression was
used, so when the save command is used again the same amount of compression
is applied without the presentation of the dialog box to choose quality
levels (one must now save as to get this). It is still saving a lossy
compressed file over a lossy compressed file.

There are tests one can do to see how 'bad' all this is, depending on
workflow and edits and resaves, but I have not come over anyone who can be
bothered to do a 'definitive' whitepaper on the real world use of JPEG and
the nuts of bolts behind resaving a jpeg as a jpeg and how different vendors
approaches and different edits and image content affects all this.

Anyone out there need a topic for their thesis? <g>

Hope that makes sense.

Stephen Marsh.



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