ABSTRACT

Keywords
Visualization, ImageTree, dynamic layout, image display, image context, art, WWW.

INTRODUCTION

The ImageTree display method was developed as a result from the problems inherent in displaying high resolution images using a relatively low bandwidth media such as WWW.

Artwork as paintings are normally stored as high resolution color images scanned from the original works. Hi-res images typically have a resolution ranging from several hundreds dpi and up, resulting in file size well over several megabytes. When displaying these images on a computer screen, several problems appear:

• Loss of image resolution. Due to the limited screen space, images are often compressed to low-res thumbnail versions.
• Bandwidth problems. Depending on the image compression and resolution, transfer to the viewer may be slow.
• Loss of image context. Navigation between images becomes difficult if no visible clues of the relations between images are present.
• Static perspective. Interactive user exploration is hard to achieve compared to a real-world gallery where the visitors may walk around.

THE IMAGETREE

[ Large version |additional example1 |additional example2 ]

The images are positioned in a tree structure, with the image in focus placed as the root node and the rest of the images positioned as in a binary tree, with successive scale reduction for each level. By selecting individual images or levels in the tree, the tree may be rebuilt to place new images in focus.

Figure 2 shows an ImageTree scenario with seven images. Four states, A, B, C and D are shown, where A is the initial state - manually designed by the exhibitor presenting the images. Three selections are made: 1, 2 and 3 which result in an iterative refinement of a personal view of the total image set.

The image in focus may act as a link to further information about the specific image. In the implementation described below, this information included a high-res zoomable image.

IMPLEMENTATION

The different image sizes were generated dynamically by the WWW server in a first version, but this approach were later modified to use pregenerated images, since dynamically generating scaled images both interfered with server capacity and the caching mechanisms in common WWW browsers. Keeping image size low is important when designing WWW applications, since small low-res images are transferred much faster than large ones.

DISCUSSION

Other information display methods as the The Document Lens [4], Pad++ [1] and fisheye views [5] relies on high speed graphics and image transfer to allow users to change viewpoint in a static environment. ImageTrees compromises between image size and transfer speed by using a dynamically changing layout. The ImageTree method has been tested in a WWW environment where both users and the image artist expressed satisfaction with the method.

CONCLUSION

The successive scale reduction can be viewed as an abstraction of real world perspective, where images far from the viewer are placed at a deep level in the ImageTree.

Compared to a 3D-representations of a gallery, ImageTrees uses tree depth as distance metaphor, while avoiding traditional 3D problems such as overlapping and hidden objects.

ACKNOWLEDGEMENTS

REFERENCES

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3. Mackinlay, J.D., Robertson, G.G., Card, S.K., The Per spective Wall: Detail and Context Smoothly Integrated, Proc. of ACM CHI'91 Conf. on Human Factors in Com puting Systems, 173-179, (1991)
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