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John Tomasi 08-17-2004 04:00 PM

Recovering altered jpegs
 
Hi everyone,

Is it possible to recover an original jpeg file after changing it and
(accidentally) hitting the save button?

My situation is this ... After adjusting the levels on a jpeg, I
intended to save it in a lossless tiff format. However, I mistakenly
saved it as a jpeg. I know that saving changes to a jpeg degrades the
image, so I was wondering if the original, undegraded image was
floating around in a temp folder somewhere.

Any advice would be much appreciated!

John Tomasi

JustaPawn 08-17-2004 04:31 PM

Re: Recovering altered jpegs
 
<< Is it possible to recover an original jpeg file after changing it and
(accidentally) hitting the save button? >>


Well, if you're using Photoshop, and you haven't quit the file, you can go back
to when you opened it or any place in between with the history palette.

Pete 08-17-2004 04:58 PM

Re: Recovering altered jpegs
 
On 17 Aug 2004 16:31:38 GMT, JustaPawn wrote:

> Well, if you're using Photoshop, and you haven't quit the file, you can go back
> to when you opened it or any place in between with the history palette.


.... or with almost any editor, simply use Undo until you get back to the
original version, then Save As.

John Tomasi 08-17-2004 05:36 PM

Re: Recovering altered jpegs
 
Thanks for your responses, JustaPawn and Pete.

I'm no expert, but my understanding is that because jpegs are lossy,
everytime you click the "save" button, your image will lose data from
your image. So, if I travelled back on the history palette and saved it
again, I'd degrade the jpeg even further than if I just left it as is.

I'm happy with the changes I made to the photo, so that's not the issue.
The issue is the quality of the image file.

Or maybe I'm just overthinking this. Is saving a jpeg once or twice that
big a deal in terms of file quality?

IMKen 08-17-2004 06:44 PM

Re: Recovering altered jpegs
 
This is the reason I always work on a duplicate of the image rather than the
original. First thing to do when you open an image for editing is duplicate
it and close the original.

Ken


"John Tomasi" <doppler9000@yahoo.com> wrote in message
news:82840b18.0408170800.5174094d@posting.google.c om...
> Hi everyone,
>
> Is it possible to recover an original jpeg file after changing it and
> (accidentally) hitting the save button?
>
> My situation is this ... After adjusting the levels on a jpeg, I
> intended to save it in a lossless tiff format. However, I mistakenly
> saved it as a jpeg. I know that saving changes to a jpeg degrades the
> image, so I was wondering if the original, undegraded image was
> floating around in a temp folder somewhere.
>
> Any advice would be much appreciated!
>
> John Tomasi




James Silverton 08-17-2004 07:06 PM

Re: Recovering altered jpegs
 

"IMKen" <imken@hawaii.rr.com> wrote in message
news:kmsUc.7045$aB1.6400@twister.socal.rr.com...
> This is the reason I always work on a duplicate of the image rather

than the
> original. First thing to do when you open an image for editing is

duplicate
> it and close the original.
>
> Ken
>
>


You can go the opposite route by making the folder read-only which
will enforce renaming or releasing.


--
James V. Silverton
Potomac, Maryland, USA


Jeremy Nixon 08-17-2004 07:19 PM

Re: Recovering altered jpegs
 
John Tomasi <doppler9000@yahoo.com> wrote:

> I'm no expert, but my understanding is that because jpegs are lossy,
> everytime you click the "save" button, your image will lose data from
> your image. So, if I travelled back on the history palette and saved it
> again, I'd degrade the jpeg even further than if I just left it as is.


No, that's not the case. The jpeg compression is what loses data; what is
still sitting in Photoshop is not changed in any way by saving it. So
you can save to jpeg every 3 seconds and it's still only one "generation"
of loss.

In your initial inquiry it sounded like you meant to save the modified
picture as a copy, and wanted to preserve the original jpeg as-is. That,
indeed, will now require some loss due to the jpeg compression, even if
you go back in the History and re-save the unchanged picture. However,
if you want the picture as-is after editing, then, no big deal -- saving
it as a jpeg will mean one generation of compression loss, not one for
each time you hit "save".

> Or maybe I'm just overthinking this. Is saving a jpeg once or twice that
> big a deal in terms of file quality?


Save it using very low compression and you won't notice the difference.

--
Jeremy | jeremy@exit109.com

Alan Meyer 08-17-2004 08:05 PM

Re: Recovering altered jpegs
 
"John Tomasi" <doppler9000@yahoo.com> wrote in message
news:hmrUc.14390$Tr.746766@news20.bellglobal.com.. .
> Thanks for your responses, JustaPawn and Pete.
>
> I'm no expert, but my understanding is that because jpegs are lossy,
> everytime you click the "save" button, your image will lose data from
> your image. So, if I travelled back on the history palette and saved it
> again, I'd degrade the jpeg even further than if I just left it as is.
>
> I'm happy with the changes I made to the photo, so that's not the issue.
> The issue is the quality of the image file.
>
> Or maybe I'm just overthinking this. Is saving a jpeg once or twice that
> big a deal in terms of file quality?


The JPEG compression scheme takes advantage of the fact
that the eye can't discern very slightly different colors easily.
It eliminates very slight differences in order to reduce the total
number of different colors that get saved in each small section
of the image. Each time you call it up and save it again, it
re-evaluates the colors and makes more compressions - thus
degrading the image. How much compression it performs
depends on the "quality" setting when you invoke the
compression. If you set the value high, you can save multiple
times with hardly any perceptible change. If you set it low,
the difference will be perceptible on the very first save.

I suggest you do this:

Get a high quality image, e.g., straight from your camera.
Save it as a new image, with a new name, e.g., image1.
Call it up again and save again as image2, and again and
again.

Do this once with a high setting and once with a lower
setting.

Then look at the images carefully and compare them.

It will tell you more about what's acceptable to you than
any amount of advice from experts.

For me, I use software that saves images with quality
settings from 1-9. At 9, I get an average of about 10:1
compression from the original uncompressed size. Saving
at 9 again makes it a bit smaller, but not much. With my
software and my own personal preferences, I find that
saving it several times is not a problem.

Alan



Alan Meyer 08-17-2004 08:18 PM

Re: Recovering altered jpegs
 

"Jeremy Nixon" <jeremy@exit109.com> wrote in message
news:10i4miodt7vf473@corp.supernews.com...
> ...
> No, that's not the case. The jpeg compression is what loses data; what is
> still sitting in Photoshop is not changed in any way by saving it. So
> you can save to jpeg every 3 seconds and it's still only one "generation"
> of loss.

....

You're right, but I'm not sure that's what John did.
If what he did was save the modified image over
the original, obliterating the original, then he has
permanently lost some information unless he's
got another copy of the original file stashed away
somewhere.

Also, I'm not sure he's using Photoshop.

Alan



Ron Hunter 08-17-2004 09:04 PM

Re: Recovering altered jpegs
 
John Tomasi wrote:
> Thanks for your responses, JustaPawn and Pete.
>
> I'm no expert, but my understanding is that because jpegs are lossy,
> everytime you click the "save" button, your image will lose data from
> your image. So, if I travelled back on the history palette and saved it
> again, I'd degrade the jpeg even further than if I just left it as is.
>
> I'm happy with the changes I made to the photo, so that's not the issue.
> The issue is the quality of the image file.
>
> Or maybe I'm just overthinking this. Is saving a jpeg once or twice that
> big a deal in terms of file quality?


First, it is the process of recompressing the JPEG picture that loses
data. Saving it just saves that recompressed, changed, picture. If you
return to the original image data, saved by the software, and then save,
a well-written program will NOT resave the data, so no further data loss
would take place.
Unless we are talking about several (say 6 or more) saves, loads, edits,
and saves, then you probably won't seen any noticeable change in the image.


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