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judge_dredd Feb 1, 2005 11:20 PM

Hey everyone,

This may be a bit of a daft question, but here goes. I know that jpegs are a lossy format and that say editing a jpeg and saving it can result in some lost quality. As for the amount of quality lost I'm not really sure but I'm guessing you would have to edit and save a high quality jpeg many times before it visually degraded. The question I have, is does this degradation apply if you are simply copying the jpeg, say from a computer to a cd-r to another computer. I don't really think so but I just want to double check.


Norm in Fujino Feb 2, 2005 1:41 AM

No, merely copying the photo doesn't cause the photo to be opened and resaved, so nothing is lost. FWIW, when modifying a JPEG photo in PSP or PS, be sure to set the compression ratio for the lowest (highest quality) value if you want to get the best results when resaving, and also save to a new (different) name from the original so that you leave the original intact and unmodified.

Stevekin Feb 2, 2005 5:57 AM

While all of this is true, you might also want to consider saving in the native format to your editing software. ie, PSD in Photoshop. This is a lossless format and enables you to keep all of your editing, layers etc, until you are sure you have finished. And remember to do as Norm in Fujino said, save as 'different name' to keep your originals. I tend to just add EDIT to the end of the file name for convenience.


judge_dredd Feb 2, 2005 10:03 AM

Thanks guys,

Great advice.

BillDrew Feb 2, 2005 5:31 PM

Good points above. I'd add that you should save a dopy of your original exactly as it comes from the camera with no editing or changes of any kind. That is your digital "negative": don't mess with it.

If you have the unaltered orginal, it doesn't much matter what you do with the copies. You can always go back and start over no matter how badly you mess up the editing or if you save it at 500x400 pixels with very high compression.

JimC Feb 2, 2005 6:32 PM

You may want to take a look at Mike Chaney's October 2004 Tech Corner Article:

JPEG Images: Counting your Losses

BTW, as BillDrew already mentioned, always keep your originals and work with copies. It's too easy to mess something up. Even if you're not concerned about degradation,you may be later, and a better way to edit the originals may come out.

Youcan also lose some information about camera settings contained in IPTC/EXIF headers with many image editors when saving files.

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