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Old Aug 8, 2006, 10:14 AM   #1
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Hello

I am trying to amend some copyright details in photos I've taken using a Samsung Digimax L85. The photos are at highest quality JPEG, at 8MP.

Every time I try to amend the copyright details, the JPEG OFFSET changes.

JPEG OFFSET ORIGINAL: 37746
JPEG OFFSET CHANGED: 37732

I decided to work only on copies of the original photos until I was certain nothing else was amended bar the copyright details. Good job I did as the JPEG OFFSET was changed. I then changed the copyright back to the original, but as expected, it just changed the offset number to something else.

I have tried various programs (Exifer, ExifEditor and Exif Pilot) and all have changed the JPEG OFFSET, but each one is different. Bar this and the copyright, no other changes appear to be made to the EXIF data.

Does any one know what the JPEG OFFSET is? I've tried to search for it on the Internet but all I get is people listing their full exif data whilst talking about something else unrelated

I am looking to amend some EXIF times, where I forgot to switch from British Summer Time to European Central Time. However no doubt the problem will exist when I do that.

I am wondering whether I can amend the JPEG OFFSET in ExifEditor. However, I don't know whether the offset change is a fundamental change, made to the JPEG image itself.

Thank you for your time

Kind regards

Timothy Langner
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Old Aug 8, 2006, 11:08 AM   #2
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You could try asking inthe Exif forums, http://www.exif.org/forum/
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Old Aug 8, 2006, 3:41 PM   #3
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Hi Sintares

Thanks for the link. Most helpful.

I will ask my question in that forum.

Kind regards

Timothy Langner
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Old Aug 9, 2006, 10:31 AM   #4
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Tim,

In a JFIF file the JPEG OFFSET references the start of the compressed JPEG image data. Whenever you change anything in the Exif, the offset has to change, otherwise software which attempts to decode the file would never be able to find the actual image.

Stuart
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Old Aug 10, 2006, 9:52 AM   #5
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Hi Stuart

Thank you for your interesting and helpful reply. I know understand now what the offset refers to, and the fact it doesn't do anything to my the image part of the file.

I had been concerned that the offset number change was due to my jpeg image being resaved when the exif data was amended. Had that been the case I didn't want to make any EXIF changes to the original files.

Kind regards

Timothy Langner
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Old Aug 11, 2006, 3:34 AM   #6
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Hi Tim
Quote:
it doesn't do anything to my the image part of the file.
Nothing you can do to the Exif will change the image data. The Exif tags that relate to the image, such as width and height, are written by the software that saves the image (and of course have to be).



Quote:
change was due to my jpeg image being resaved
You're OK with Exif editors, because they'll save the image data as is without changing it; just adjust things like offset, etc. as necessary.

As you know though, every time you edit and save a jpeg in an image editor the image data is re-compressed and will deteriorate in 'quality' over a number of saves.


Stuart
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