| Last updated | 2003-12-01 16:41:21 EST |
| Doc Title | Image Class and JPEG2000 |
| Author 1 | John Weise |
| CVS Revision | $Revision: 1.6 $ |
Image Class supports JPEG2000 compressed images in the JP2 format. The Kakadu Software Development Kit was used to implement functionality nearly identical to that offered with MrSID from LizardTech. High compression ratios using wavelet compression, multiple image sizes, zooming, and panning are all included.
Command line compression and expansion utilities for Solaris and Linux are provided with DLXS to paying DLXS subscribers. These utilities may also be licensed from Kakadu Software. We are simply using the "demo" utilties, kdu_compress and kdu_expand.
The University of Michigan Library has a license for the Kakadu Software (SDK) that allows non-commercial redistribution of compiled applications. Visit Kakadu Software to learn more about additional licensing options.
The kdu_compress utilitiy accepts a long list of options that will not be explained here. The following will generate a JPEG2000 compressed JP2 file with roughly 20:1 compression and 5 images sizes. The rate option is used to control the amount of compression. The Clevels option is for controlling the number of image sizes.
kdu_compress -i filename.bmp -o filename.jp2 -Clevels=5 -rate 1.09
David Taubman, creator/owner of Kakadu Software stated in the online discussion forum, "The JPEG2000 standard has no explicit definition for a quality factor (neither does the JPEG standard for that matter). As a general rule, the rate-distortion slope threshold often turns out to be a more reliable indicator of quality than the bit-rate. I would suggest compressing some images which are typical of your application to the point which you believe represents a sufficient quality, then looking at the slope thresholds reported by "kdu_compress" in its verbose (default) mode. You can then compress all your images, using the "-slope" option."
Using -slope to control quality has not yet been explored at the University of Michigan.
It is a bit of a problem that the Kakadu utilities do not support a wider range of formats for input and output. It is not a priority of Kakadu Software to add additional formats. There are many other existing utilities for converting files to one of the formats supported for input. ImageMagick is probably best known.
Expansion of JPEG2000 compressed image files in the JP2 format can be done with kdu_expand. The "-reduce" option is used to specify the desired image size referenced by level (see -Clevel compression option above). Note that the largest size is level 0.
kdu_expand -i filename.jp2 -o filename.bmp -reduce 2
QuickTime (Macintosh only at this time) is capable of opening JP2 files created by Kakadu. In fact Apple uses Kakadu for JPEG2000 support in QuickTime.
Image Class middleware uses the cjpeg program to convert output from kdu_expand to create a JPEG compressed image to send to the browser. cjpeg is part of libjpeg and is often included on UNIX systems by default. If not, it can be found on the web.