Soft Caching Project


The soft caching (SC) project got started in 1997 and has involved a collaboration between groups at the University of Southern California and EPFL in Lausanne, Switzerland. The basic goal is to provide specific caching strategies for images. The traditional proxy caching currently used treats all cacheable objects in the same manner, i.e. whatever the object contents the same algorithm is applied to determine whether the object remain in the cache or be removed. We call this "hard" caching, as objects can only be in the cache or not. Instead, we propose that images can be dealt with in a different way. The idea of "soft" caching is that instead of removing images to make room for new objects, these images can be recoded at a lower resolution. When the level of recoding is low, i.e. the image quality still high, the user is unlikely to require additional bits. Even at very low quality, the user may choose not to reload the page (and thus send a request to the server), thus again resulting in overall access savings. A more complete description of the soft caching ideas can be found in our papers Soft Caching: Web Cache Management for Images , from the IEEE Signal Processing Society Workshop on Multimedia, June 1997 and Design and Implementation of a Soft Caching Proxy , from the 3rd Intl. WWW Caching Workshop, Manchester, England, June 1998 (also available in postscript format here .

We are currently using progressive JPEG to encode the images and successive recoding steps result in lower quality images at the same spatial resolution. We are planning to experiment with other scalability methods as well. Other directions of work include experimentation with various types of replenishment algorithms.

We have a soft cache currently running in our lab. This is a modified version of the Squid Cache which handles JPEG images. In this page you can find links to two sites we have accessed frequently so that images might have been recoded in our cache. Also, the FAQ page includes some instructions on how to have your browser use our two proxies as caching proxies. We currently use a very small cache size to test the recoding algorithms but plan to increase this in the near future.

Publications and current results


The SC project is currently funded in part by Rockwell Semiconductor Systems, Newport Beach, CA and by Hughes Research Labs, Malibu, CA.


If you have comments or would like more information about the project, please send email to Antonio Ortega at

Last modified: Tue Apr 13 13:54:05 PDT 1999