Efficiency of wavelet conversion

Adolf Knoll, National Library of the Czech Republic

This study was written on the basis of tests whose aim was to define applicability of new wavelet compression schemes for true colour images. The wavelet compression gives better results than classical compression schemes especially in the lossy domain. There is work in progress now to replace the well-known classical JPEG format by a more efficient JPEG2000 format. Even if the backward compatibility is said to be preserved, the new JPEG2000 features will be based on wavelet compression.

There are several solutions nowadays, which implement various wavelet compression solutions for true colour images. We wanted to find out, whether some of them are so advanced or prepared that we might consider their application for selected imaging solutions in libraries, especially for access to digitized documents.

Several image samples are shown in the study. They document the modifications occurred on the image during the lossy wavelet compression. To be able to show you the samples, it has been necessary to convert them into the PNG format in order not to loose colour depth (if converting into GIF) and information (if converted into JPEG). The PNG format has already been adopted as a web standard so that more recent Internet browsers should be able to display it at least as the in-line image. The PNG format offers the best lossless compression and true colour image that was not possible in Internet before when only GIF and JPEG were recommended.

If you see here in the below frame a small image, your browser can display PNG and you can read this study. If no image is seen, you should install a higher version of your browser; newer versions of both Microsoft Internet Explorer and Netscape Navigator (Communicator) browsers are able to display PNG.

Because of using PNG, the overall volume of all the HTML document with PNG images is higher than usual web documents: it has ca. 844 KB. Consider this when clicking to read the study.

31 August 2000