Rewrite jpg's to many times? Degrade Pictures?

[Quension]

I remembered, I just wanted to point out that some apps like XnView and IrfanView tend to blur the issue in terms of UI, and give some background for those trying to intuit what other apps might do.

I fully agree with your reaction though; basic tagging has nothing to do with changing image data, and it takes a special kind of dumb to conflate or ignore the issue when creating an application.

[mattdm]

Originally Posted by wll

You must rename it, or it will, over repeated openings and saves loose image quality.
EVERYTIME you save a JPEG rename it ... just a number or letter after the original name will do.

Just for the record, the above doesn't actually make any sense. Presumably the advice is to start with the same original each time, so that each changed jpeg is only second generation.

For multiple generations (when the data changes, not just the EXIF — Mark's totally right there) there is some loss, but it takes a surprisingly long time for jpeg artifacts to add up to the point of visibility. I saw a test somewhere a long time ago where it took something like 600 repeated saves to see the difference. And, if you use the same jpeg settings to re-save the effect will be minimal (because you can't throw away the same data twice).

Therefore, if you have to do it, go ahead. But as a general part of your workflow, try to avoid it.

Oh, and it's also worth noting that rotation and some cropping can be done totally losslessly, but that a lot of software does get that wrong.

[wll]

Originally Posted by mattdm

Just for the record, the above doesn't actually make any sense. Presumably the advice is to start with the same original each time, so that each changed jpeg is only second generation.

For multiple generations (when the data changes, not just the EXIF — Mark's totally right there) there is some loss, but it takes a surprisingly long time for jpeg artifacts to add up to the point of visibility. I saw a test somewhere a long time ago where it took something like 600 repeated saves to see the difference. And, if you use the same jpeg settings to re-save the effect will be minimal (because you can't throw away the same data twice).

Therefore, if you have to do it, go ahead. But as a general part of your workflow, try to avoid it.

Oh, and it's also worth noting that rotation and some cropping can be done totally losslessly, but that a lot of software does get that wrong.

mattdm,

I did not not make myself clear, I apologize.

Yes I alway keep the main JPEG and save the second copy under a different name, but I always start from the original. If I plan on doing a major overhall of a JPEG - I change it to a tiff.

wll

[buckethead]

Ok - boiling down the information from the thread so far. Thanks for all the responses and the discussion.

-using a program like iTag should not degrade as it only touches metadata
-other programs that touch the rewrite the whole data of the picture do degrade the file, but it will take a ton of resaves, so rewriting metadata a handful of times is not going to hurt anything

I see that resaving the jpg as another file would be best to save original jpg, but then stuck with dups and not what I want as I have the files backed up or active on 4 different hard drives.

I am also taking away from this that even if the picture is degraded somewhat it should not get to the point, unless I resave a ton, that I can not print out at 4x6 or 5x7.

[Mister Guy]

Originally Posted by buckethead

Ok - boiling down the information from the thread so far. Thanks for all the responses and the discussion.

-using a program like iTag should not degrade as it only touches metadata
-other programs that touch the rewrite the whole data of the picture do degrade the file, but it will take a ton of resaves, so rewriting metadata a handful of times is not going to hurt anything

I see that resaving the jpg as another file would be best to save original jpg, but then stuck with dups and not what I want as I have the files backed up or active on 4 different hard drives.

I am also taking away from this that even if the picture is degraded somewhat it should not get to the point, unless I resave a ton, that I can not print out at 4x6 or 5x7.

The whole resaving jpeg degrading thing falls pretty solidly in the realm "very often technically true, but widely overblown." Yes it happens, very similarly to how driving your car wears down your tires. Eventually, you'll have a blow out. Certain people in certain very high performance vehicles in certain conditions can even tell after one run that their tires are no longer suitable.

You, personally, are very unlikely to notice and/or care.