HOME
TOPICS
SEARCH
ABOUT ME
MAIL

 
A new, lossless format has been designed to replace the old JPEG method.
 technofile
Al Fasoldt's reviews and commentaries, continuously available online since 1983

T e c h n o f i l e
Lossless JPEGs? Yes, if you use the new JPEG2000 format


March 21, 2004


By Al Fasoldt
Copyright © 2004, Al Fasoldt
Copyright © 2004, The Post-Standard

   For years, JPEGs have been the bad boys of the image world. Images saved as JPEGs have always emerged from the image-compression processing with something missing.
   JPEG (also called JPG) is a "lossy" image format. It strips out details each time you save a JPEG image. Successive file operations can be disastrous, leaving digital photos rough and "spiky" as details are peeled away each time you save the image file.
   This happens even when you use software that lets you adjust the JPEG quality level to its highest setting. In the comparatively few programs that provide such an adjustment, you might be misled into assuming that a "high quality" JPEG will maintain image quality. Not so; the nature of the relatively old-fashioned JPEG process guarantees that there is no such thing as a lossless JPEG.
   But the old era is ending. A new, lossless format designed to replace the old JPEG method has been gaining popularity. I've been testing it with my own images with great success.
   The name of the new method, JPEG2000, is more than a little misleading, so let's make something clear right away: JPEG2000 (spelled that way, as one word) is not directly related to the old JPEG format. It's a distant cousin at best. It doesn't work the same way.
   The good news about JPEG2000? Unlike the old JPEG format, JPEG2000 has a true lossless mode. You can choose to save your images without degradation, and successive file operations won't cause a problem. They won't shrink as much under lossless mode as they would the old-fashioned way, but they'll get quite a bit smaller without losing quality. That's great.
   An optional feature of JPEG2000 of lesser interest to photographers is its super-squeeze capability. It can compress images an incredible amount without much loss. I took a TIFF version of a Hubble Space Telescope photo (a 182-megabytes image) and compressed it using JPEG2000. The compressed version has the same resolution (7875 pixels by 8089 pixels) and looks almost exactly the same, but it's only 1 megabyte in total size. The JPEG2000 processing reduced the file size to less than 1 percent of what it had been. That's simply amazing.
   But photographers should stick to lossless mode. When I saved the 182-megabyte image using JPEG2000's lossless compression, the file size dropped to 119 megabytes. That's a 37 percent savings in size.
   I've been using JPEG2000's lossless mode for all my archival image storage for the last few months. Vacation image collections that took up three CDs (or, sometimes, two data DVDs) now fit on a single disk -- a huge benefit when you're trying to find a photo. Grayscale image scans of my photos from Vietnam were compressed even more than my color photos, so I was able to get far more onto single disks than before. (You can see samples of my Vietnam photos at www.stripes.com/photoday/mekong.)
   Many image editors and photo viewers do not yet support JPEG2000. If you have a program that can use Photoshop plugins, you can get an excellent free JPEG2000 plugin from www.fnordware.com/j2k. It's the one I use. There are both Windows and Macintosh versions.
   Photoshop plugins work with Adobe Photoshop and Adobe Photoshop Elements 2.0 and with many other non-Adobe image editors. Check your software's help menu to see if your program supports Photoshop plugins.