Tuesday, November 27, 2007

Quick thought about JPEG2000

I promised myself in October that I would spend time reading and learning about JPEG2000, and that I would blog about the standard. The end of November is almost here and I've done none of that. Sigh.

Reading the technical details about the standard takes me back to my days in IT, when I would spend hours reading about something technical, then run a few "experiment" in hopes of mastering it (or more likely fix a problem that had been tossed my way). What I need are the "Clif Notes" or the quick whiteboard session with Scotty from Star Trek to cut through and tell me what I really need/want to know about JPEG2000. (Or maybe I need the "Easy Button" from Staples.)

Here's what I do know about JPEG2000:
  • It should have been named something different because comparing it to the JPEG we know and love doesn't do it justice.
  • It is more versatile that I suspect most people realize.
  • It is should not be feared.
  • We should be using it.
  • The software for using/creating JPEG2000 needs to be more widely available/known.
  • Library consortia (and others) should be offering mini-workshops on JPEG2000 to help people feel comfortable with it and use it.
  • It needs someone to do something really, really cool with it in order for people to stand up and take notice (and adopt it).
BTW I'm off on another business trip tomorrow and I will again promise myself to read the documents I have on JPEG2000, although staring out the train window on my way to NYC and Long Island sounds good too.


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6 comments:

jordon said...

Jill, you've done alot of good work raising awareness of this issue. Don't sell yourself short!

The following is my main concern about the JPEG2000 format.

As I understand it, JPEG 2000 files are just the original TIFF, but compressed. So theoretically, if you wanted to backtrack to the original TIFF master, you could.

However, the main question is whether or not backtracking to the TIFF can result in some kind of loss in quality. I had someone explain it to me this way. What if you squished a shirt in your suitcase, and when you unpacked it, it remained somewhat wrinkled forever. I can't get a clear answer on whether or not there's a potential for a JPEG2000 file not to look like the original TIFF if you uncompressed it. Or, if you compress it and uncompress it multiple times.

When I ask this question, most people say, "Well, that's why we hang on to that TIFF master," implying that they are concerned about loss in quality if they decided to backtrack to the TIFF. But then what's the point of having the JPEG2000, you know? I want less complexity in my file management, not more.

Jill Hurst-Wahl said...

Jordon, I'm not sure (from my limited knowledge) that I would call JPEG2000 a compressed TIFF. Compression tends to imply "lossy" and JPEG2000 is [can be]lossless. JPEG2000 also contains more data (again if I understand correctly). And JPEG200 can be used for video.

So in real layman's terms, J2K gives us both the TIFF and the JPEG in one file format, as well as additional data.

My assumption is that the J2K file understands how to give you the view of the image that you want without altering the file (and this losing data).

Perhaps we need to build an FAQ of the questions real people have about J2K? mmm....

Ron Murray said...

In thinking about JPEG 2000 it is necessary to distinguish image compression as a reduction in file size from image quality loss as a function of image encoding.

Previous image formats that reduced file size also reduced image quality, but this is not the case with JPEG 2000. The mathematical representation of the image is not subject to loss upon repeated file saves like regular JPEG is.

Try it Yourself!
A JPEG 2000 plug-in has been provided with the last three or so versions of Adobe Photoshop. Look on the install disk where the extra plug-ins are or see if you can download it from their website. See also the very nice Fnord plugin at http://www.fnordware.com/j2k/

Use the Photoshop "Calculations..." command to subtract original from J2K images ("Difference" with greyscale). The Histogram of the image will show you how many pixels change as a function of the quality setting.

Hints: With the lossless setting, there are no pixel changes whatsoever. With minimally lossy settings, you will see the noise pattern from the camera/scanner show up first, followed by some image detail with higher settings.

mpg said...

Very broadly speaking, you can think of it like this, perhaps:

JPG stores only a "lossy" version of the file, and TIFF stores only a lossless version of the file.

JPEG 2000, however, can store the file at any a range from lossless to lossy (but not both), settable at encode time.

Once encoded into JP2 format, images can later on be further compressed. There's no going back, though -- once you throw away data, it's gone.

Just to keep you on your toes, note that in lossless mode, typical images will see about a 2:1 compression ratio -- not "1:1" as one might naively expect. This is an artifact of the encoding scheme, though, not because any data has actually been lost. (Typical images will be "visually lossless" up to 15:1 or so.)

-mpg

Ron Murray said...

Expanding on MPG's comments, consider this about relative file sizes:

* The image captured by a camera can be described in a number of ways.

* Some of these descriptions can be longer than others - in terms of bytes. The JPEG 2000 description for an image takes fewer bytes than a TIFF version of the image.

* Even though an image may cover a large number of pixels in area, there may not be much detail or color variation in the image. Under a TIFF regime, the description of this image takes up many bytes in file size as that of a highly detailed image.

* A JPEG 2000 image description varies according to the actual image detail or color variation in the image. (Unfortunately, "noise" introduced by the camera/scanner also counts as detail.)

Peter Murray said...

For what it's worth, and to expand on Ron's comment above, my own thoughts about lossless JPEG2000 compression -- including image generation and testing -- can be found at http://dltj.org/2007/05/lossless-jpeg2000/.