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gbr2004uk

Joined:

Jan 08

Posts: 154

gbr2004uk says:

jpeg deterioration - re-opening?

I got a bit confused today (confession!) - I was telling someone that if they kept on re-opening and closing their jpeg collection images, they'd cause deterioration in quality, but then I said, if you send the pics to someone on a CD and they open/close x no. of times, it wont cause deterioration cos they wont be saving the images on the (non-rewritable) CD.

But then I thought, wait a minute!  What's the difference between it being on a CD or the computer HD?  As long as you don't keep re-saving the images .............. but that didn't sound right either.  I seem to remember someone saying that the mere fact of opening and closing a jpeg stored on your HD would cause loss of quality (even without resaving) - and quite quickly soon.

And they I realised I'd forgotten the truth!  So what is the truth out there?  Many thanks for enlightenment in advance!  Cheers

Brian

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Dave Parry

Joined:

Feb 08

Posts: 1507

Dave Parry says:

Re: jpeg deterioration - re-opening?

Hi Brian,

A jpeg file only deteriorates when it is saved, there is no loss of quality caused by opening and closing the file.

Kind regards, Dave.

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StephenBatey

Joined:

Nov 05

Posts: 10102

StephenBatey says:

Re: jpeg deterioration - re-opening?

And based on my tests, 6 saves will make a noticeable difference. But it will depend on the program doing the saving, and the settings. jpg is a "lossy" format - it is designed to compress by dropping out small details on each save, to reduce the size. Eventually it becomes noticeable.

Old photographers never die - they just stop developing

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Dave Canon

Joined:

Mar 06

Posts: 4099

Dave Canon says:

Re: jpeg deterioration - re-opening?

The deterioration depends on another factor as well. It depend if you made any changes to the image. Even if you make small changes (particularly global changes such as curves or Levels), the deterioration can be fairly rapid each time you save. However, if you do not re-save the image should be the same each time you open the file.
 

Dave

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gbr2004uk

Joined:

Jan 08

Posts: 154

gbr2004uk says:

Re: jpeg deterioration - re-opening?

Thanks to all for those very clear replies!  cheers. -- Brian

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