2/15/2013

Caring for your JPEG's


Did you know that every time you open and save a JPEG file you lose a little bit of image quality?

JPEG's are a compressed file format - what this means is that every time you save a JPEG file it compresses it - in others words it gets rid of a little bit of data in order to make the file size smaller.

When you take an image in your camera, it's in RAW.  It takes all the detail that is in the scene and records it. At this point if you have opted for your camera to take shots in RAW, that's exactly the way it will stay. If, however, you choose JPEG, the camera throws away some of the information that has been recorded then compresses the file to make a JPEG.  This is not about the whole RAW Vs JPEG debate, but rather to make you aware that if you choose JPEG in camera, that is your first compression. (I shoot a lot of images in JPEG - in fact all my "everyday" shots are in JPEG, because I don't feel the the need to have that extra information, and range of tones that shooting in RAW gives me, for these shots, nor do I have the time to edit every single photo that comes out of my camera! Just so you know)



Let's say you open that JPEG file on your computer to view it, save it, then close it again.  The file compresses just a little bit again. If you open it again, do some edits and save it again - once again you lose just that little bit of data. You then open it to show your friends and save and close it and, yep, it compresses again and another little bit of data is lost.

Now, I have to say that you would probably have to open, save and close a file at least 20 or 30 times before you even begin to notice this loss of data in the form of image degradation, but it's good practice to limit the number of times you open and save the file as a JPEG so you retain as much image quality as possible.

If you shoot in JPEG and edit in Photoshop / Photoshop Elements, save the file as a PSD file, this allows you to go back in and change the edits at a later date without having to resave it as a JPEG. When you are happy with the editing, save a copy as a JPEG, but always keep your original and if possible, a copy of the PSD file. This way you will limit the number of saves, plus,  if you do have an images you view reguarly, you can always save a new JPEG copy from your saved PSD file - keeping your JPEG's looking pristine for years to come!

Other Posts You Might Like:

My Editng Workflow
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7 comments:

Jan said...

what about jpegs saved in smugmug? do those lose some of their quality each time you open them up? or because the jpeg is on a host site, it doesn't?

Audrey said...

You are not opening and saving the original file each time you view on Smugmug as it's really a file preview that you see. They basically make copies of your originals for viewing but your original remains untouched. The only way the original is accessed is when you download it. So you can view them online without any fear of image degradation! (NB When they apply sharpening for web it's only for these viewing "copies" - your originals are not sharpened in any way) Let me know if that answers your question!

Jan said...

yes, thank you! glad i can flip through them til my heart's content! i go through my iphoto images all the time. i wonder if they're getting degraded each time i open them. seems like apple would have a fix for that.

Anonymous said...

Why does the image degrade when you open and close the file? Without a save event, the contents of the file should not change, correct?

Anonymous said...

Can we see some evidence on jpeg degradation from opening and closing the same picture over and over? I'll believe it when I see it.

Audrey said...
This comment has been removed by the author.
Audrey said...

It might not be true, but it is something to be aware of. Saving a JPEG certainly compresses and then loses data, so I have increased the number of times in the post I have used the word "save" rather than just close, hopefully this will amend it enough for you.

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