In One Go

The benefits of Lepton are most apparent in cases where you need to compress a lot of files. The shell script in Listing 3 recursively searches through the directory from which it was called, looking for JPEG files and automatically converting them to Lepton format. In you comment out line 4 and remove the comment mark before line 6, the script deletes the output JPEGs, instead of moving them to the jpegs/ directory. The script in Listing 4 converts Lepton files back into JPEG format.

In both cases, it is a good idea to adapt the scripts to local conditions. For example, if you want the scripts to automatically convert the images, replace the period character after find with the path to the directory where the scripts are located. Then create an appropriate Cron job that executes the script at the prescribed times.

Monitoring Folders

If you want to add even more automation, you can use Inotify tools [6] to monitor a directory for changes. Inotify works like a daemon that continuously checks whether anything has changed in the directory. If a JPEG file is added to the directory, you can thus automatically convert it to Lepton format. The script in Listing 5 gives you an idea of how to use Lepton with Inotify.

Be sure you don't put the LEP directory in a folder monitored by Inotify, or you will trigger an infinite loop.

Conclusions

Saving 20 to 25 percent of the space for a JPEG file might not seem like a great deal, but in today's mass of ever-larger image collections, the savings could quickly add up to several gigabytes of disk space.

Lepton is generally much better than all other solutions at compressing JPEG images, although the shortage of good documentation makes using the program difficult. Support for the Lepton format in common image-processing programs and image viewers is still be pending, but it shouldn't take too much longer.