Conclusions

The Electronic Beowulf image delivery system presented here is very much a prototype, however the results we have seen have been very encouraging. In fact, getting this far has proved to be easier than we had anticipated. The main outstanding issue is the need to maintain the quality of the generated images. We will continue to develop the prototype, probably along the following lines:

• Extend the system to cope with a hierarchy of overlapping images.

• Support different image formats (e.g. JPEG), for browsers that support such formats inline. It is envisaged that an HTML form would allow users to specify their preferences and encode this information in the generated URLs.

• Adapt to differing user preferences. If users are connected over a fast communications link and have large displays, then they may wish to have a larger viewport onto the image. This information could be specified using an HTML form and encoded as described in the previous point.

• Performance tuning. Although a 100,000 pixel image takes only a couple of seconds to generate, multiple concurrent accesses and larger windows will slow the system down and adversely affect response times.

• Reduce storage requirements. Currently each folio is stored as a set of four image files (one at each resolution) with each pixel stored as a three-byte RGB value. As the pre-processed images contain a limited number of colours, we are exploring other image formats that comprise of a colour table followed by an array of pixels values, which are two-byte indices into the colour table. This should lead to a file size reduction of a third, which represents about 9 MB per image.

The techniques described in this paper are descussed in more detail in a book by the author of the paper, to be published later this year.