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Everybody needs to know one important fact, because ignoring it can lead to JPEG Rot.
 technofile
Al Fasoldt's reviews and commentaries, continuously available online since 1983

B l o g
Don't let your pictures suffer from JPEG Rot


July 23, 2006


By Al Fasoldt
Copyright © 2006, Al Fasoldt
Copyright © 2006, The Post-Standard

   JPEG rot? It's a real problem.
   But it doesn't happen all by itself. JPEG -- also spelled JPG, and always pronounced "jay-peg" -- is the most common image format worldwide. Web sites use it for their Web-page images and all consumer digital cameras (the non-pro kind) use it for their pictures.
   It's so popular because JPEG images don't take up much space. A lot more JPEGs can fit on a camera's memory card than, say, TIF images even when they show the same pictures. Web pages load a lot faster in your browser when the files that represent images are smaller.
   That's good. And bad.
   JPEGs are compressed to make their files smaller. A very clever technique takes details out of the picture in ways we usually don't notice. It's not simply a matter of taking out the wart on Uncle Henry's nose or the spot on Aunt Mim's glasses; JPEG compression takes a little out of just about everything.
   Most casual photographers probably spend years taking hundreds or even thousands of pictures without worrying or even knowing about JPEG compression. But everybody needs to know one important fact, because ignoring it can lead to JPEG Rot.
   Ready? Copy the next sentence and paste it into something you'll keep for a long time -- paste it into an e-mail to yourself, maybe.
   Every time you alter and resave a JPEG image, it loses some of its quality.
   That means all these things:
   If you crop a JPEG image and then save it, you've just added to JPEG rot.
   If you fix the colors in a JPEG image and then save it, you've just reduced the quality.
   If you get rid of some red eye in a JPEG image and then close and save the image, you've just made the picture fuzzier.
   In other words, JPEG compresson happens every time you save a JPEG image, and repeated compression and recompression makes a JPEG picture look worse. It takes on a roughness, a real ugliness. We've all seen it. You've seen this in your own pictures if you've saved, edited and resaved them, especially if you do it multiple times.
   (Crop? Save. Take out a reddish cast? Resave. Fix the skin tones? Resave. Whups, fix them again since they're still greenish? Save. By this time, the picture is rough looking and coarse, as if it came from a terrible camera.)
   The solution is extraordinarily simple. It's so easy and so common-sense that you will kick yourself when you hear it. (Be gentle. Medical costs are out of sight these days. A light slap upside the head might be better.)
   How to avoid JPEG Rot: Make a non-JPEG copy of each photo and use it instead of the original JPEG for all editing. ("Editing" means doing anything to the picture that requires you to save it again.) My choice of a non-JPEG format is TIFF.
   The non-JPEG copy requires no fancy software. Your image editor or viewer should be able to do it -- if it doesn't, consider getting better software! -- but if you know of no way, install Irfan View if you use Windows (from www.irfanview.com) or simply use the built-in conversion method in iPhoto if you use a Mac OS X computer. (The "Export" menu item in iPhoto lets you save any number of photos as TIFFs. Import the TIFF versions back into iPhoto after the conversion.)
   Here's the routine I am trying to get you to adopt:
   1. Get your photos off your digital camera.
   2. Select all the ones you want to keep. (Be generous. Even poor photos might have a historical or family value.)
   3. Copy all the originals that are worth keeping to a folder marked for the date you took them on the external hard drive.
   4. Create a folder within that folder called Edited.
   5. Make TIFF (non-JPEG) copies of all the original photos. Keep them on your computer (in Picasa, in iPhoto or in whatever program you use for editing) and go ahead and edit them. Crop them, fix the colors, whatever you want. After you have edited them, copy or move them to the dated folder on the external drive.
   (Move them if you've finished making any changes or adjustments to them; copy them if you plan to do more editing in the near future. But be sure to copy the newly edited versions to that external drive folder after you've edited them further.)
   6. Learn to leave the original versions alone. They're only for one purpose: To replace an edited version that you've lost or messed up. Don't print any of the JPEGs (print the TIFs); don't make slide shows out of them (use the TIFs), and don't e-mail them to anyone (you've edited the mages and saved the improved versions as TIFs, so send TIFs -- reduced in size and reconverted to JPEGs for e-mailing -- instead).
   7. Never crop or edit photos in any way inside the camera. Yes, I know there are many cameras that let you do that. It's never a good thing. Do your editing with good software. Your camera is a camera, not an editing suite.
   More blog entries.