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JPEG and lossy

 
 
Conrad
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      07-20-2006
Hi,

Working with JPEG files - does opening and closing cause lossy damage
to image or do you have to perform tweaks (i.e., within Photoshop) to
cause any potential loss of quality?


TIA,

Conrad
Camp Sherman, Oregon

 
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Joe Makowiec
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      07-20-2006
On 20 Jul 2006 in rec.photo.digital, Conrad wrote:

> Working with JPEG files - does opening and closing cause lossy damage
> to image or do you have to perform tweaks (i.e., within Photoshop) to
> cause any potential loss of quality?


No. Only edits/resaves.

--
Joe Makowiec
http://makowiec.org/
Email: http://makowiec.org/contact/?Joe
 
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POHB
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      07-20-2006
Conrad wrote:
> Hi,
>
> Working with JPEG files - does opening and closing cause lossy damage
> to image or do you have to perform tweaks (i.e., within Photoshop) to
> cause any potential loss of quality?


Opening and viewing a file won't change it. Tweaking the file once it
is open still won't affect the original file until you hit Save. It is
only if you save changes and overwrite the original file that you can
affect the quality of that file. If you save your tweaks to a new
filename then your original is still available at its original quality.
If you want to make multiple tweaks across different editing sessions
then save the intermediate results in a lossless format.

 
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stauffer@usfamily.net
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      07-20-2006

POHB wrote:
snip

> If you want to make multiple tweaks across different editing sessions
> then save the intermediate results in a lossless format.


Further, in that case, save it in the native file format of your editor
(PS for Photoshop, PSP for Paint Shop Pro, etc.). If you save it to
some other format, you are likey to LOSE some of the editing
information in the editing you have been doing. For instance, if you
have created layers, and are working on them, most standard formats
will NOT save the layer info.

When editing, always save at end of session in the native format, and
do not convert to a standard format until you are SURE you are done
editing.

 
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Ed Ruf
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      07-20-2006
On Thu, 20 Jul 2006 12:03:42 GMT, in rec.photo.digital Joe Makowiec
<(E-Mail Removed)> wrote:

>On 20 Jul 2006 in rec.photo.digital, Conrad wrote:
>
>> Working with JPEG files - does opening and closing cause lossy damage
>> to image or do you have to perform tweaks (i.e., within Photoshop) to
>> cause any potential loss of quality?

>
>No. Only edits/resaves.


Actually, one need not even edit. It is strictly the saving where the
compression is applied. If you repeatedly open and resave a jpg, very
quickly the loss in quality will be come readily apparent.
__________________________________________________ ______
Ed Ruf Lifetime AMA# 344007 ((E-Mail Removed))
http://EdwardGRuf.com
 
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John McWilliams
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      07-20-2006
On 7/20/06 7:31 AM, Ed Ruf wrote:
> On Thu, 20 Jul 2006 12:03:42 GMT, in rec.photo.digital Joe Makowiec
> <(E-Mail Removed)> wrote:
>
>> On 20 Jul 2006 in rec.photo.digital, Conrad wrote:
>>
>>> Working with JPEG files - does opening and closing cause lossy damage
>>> to image or do you have to perform tweaks (i.e., within Photoshop) to
>>> cause any potential loss of quality?

>> No. Only edits/resaves.

>
> Actually, one need not even edit. It is strictly the saving where the
> compression is applied. If you repeatedly open and resave a jpg, very
> quickly the loss in quality will be come readily apparent.


If you open a jpeg in a competent graphics program, and do not edit,
there is no re-compression, and hence no loss. Programs that do
otherwise are rather lacking.

And, Ed, if you'd kindly place a sig delimiter before your tag lines,
it'd be appreciated.

--
john mcwilliams
 
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Bill Funk
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      07-20-2006
On Thu, 20 Jul 2006 08:11:54 -0700, John McWilliams
<(E-Mail Removed)> wrote:

>If you open a jpeg in a competent graphics program, and do not edit,
>there is no re-compression, and hence no loss. Programs that do
>otherwise are rather lacking.


As was said before, it's not the editing that causes loss, it's the
saving.
Open and edit a Jpeg file all you want. If you don't save it, there's
no action performed on the opened file.
Are there actually apps being marketed that will automatically save
any opened files without action on the part of the user?
--
Bill Funk
replace "g" with "a"
 
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Hebee Jeebes
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      07-20-2006
If you just open and close them and don't do anything to them or perform a
save command then it doesn't degrade. If Photoshop asks you to save when you
close then you made changes and this would cause additional image loss if
you saved it in JPG. I convert my JPGs to TIFs when I work on them so that I
don't have to worry about the JPG lossy business.

R


"Conrad" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
> Hi,
>
> Working with JPEG files - does opening and closing cause lossy damage
> to image or do you have to perform tweaks (i.e., within Photoshop) to
> cause any potential loss of quality?
>
>
> TIA,
>
> Conrad
> Camp Sherman, Oregon
>



 
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John McWilliams
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      07-20-2006
On 7/20/06 10:10 AM, Bill Funk wrote:
> On Thu, 20 Jul 2006 08:11:54 -0700, John McWilliams
> <(E-Mail Removed)> wrote:
>
>> If you open a jpeg in a competent graphics program, and do not edit,
>> there is no re-compression, and hence no loss. Programs that do
>> otherwise are rather lacking.

>
> As was said before, it's not the editing that causes loss, it's the
> saving.


Of course. But someone seems to think that just saving an open jpeg will
cause losses, which it won't with a competent image app.

> Open and edit a Jpeg file all you want. If you don't save it, there's
> no action performed on the opened file.


Of course. [see above].
> Are there actually apps being marketed that will automatically save
> any opened files without action on the part of the user?


Not that I am aware of on the Mac platform. Some allow autosave, but
they're not image apps. and you have to set same in Prefs.

Of course, all the above fairly begs the question as to what "saving"
actually means.

--
john mcwilliams
 
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Ed Ruf
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      07-20-2006
On Thu, 20 Jul 2006 12:37:13 -0700, in rec.photo.digital John
McWilliams <(E-Mail Removed)> wrote:

>Of course. But someone seems to think that just saving an open jpeg will
>cause losses, which it won't with a competent image app.


Open a file in PS CS2, choose Save As to another name. Guess what, it
recompresses. Open a file in PSP7 or 8 (as the versions I have) just
click Save. Guess what?
__________________________________________________ ______
Ed Ruf Lifetime AMA# 344007 ((E-Mail Removed))
http://EdwardGRuf.com
 
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