Flip Zooming: A Practical Focus+Context Approach to Visualizing Large Data Sets L. E. Holmquista and C. Ahlbergb aSSKKII,
c/o Dept. of Linguistics, Gothenburg University, S-412 98 Gothenburg, Sweden* E-mail:
[email protected] bIVEE
Development, Stora Badhusgatan 18-20, S-411 21 Gothenburg, Sweden E-mail:
[email protected]
1. INTRODUCTION When working with a large material, such as a document or a database, it is often desirable to be able to examine some part of the material in detail, while still retaining a contextual overview. This becomes problematic when the material has to be displayed on a computer screen. Many visualization techniques that attempt to overcome problems associated with displaying large amounts of data have been developed. The so-called focus+context visualization techniques attempt to give users an overview over the whole information (the context) while simultaneously making it possible to view or work with some part of the material in detail (the focus). Focus+context techniques include the bifocal display [7], the generalized fish-eye view [1], the graphical fish-eye view [6], the perspective wall [4] and the document lens [5]. An overview of distortion-based presentation techniques is given in [3].
Figure 1. The principles of flip zooming. When users want to see a page in detail, they click on its thumbnail representation
* Present address: Dept. of Informatics, Gothenburg University, S-411 80 Gothenburg, Sweden
Figure 2. The Zoom Browser; an un-zoomed view of a document (left) and a zoomed view (right)
2. FLIP ZOOMING We have developed a new focus+context approach to displaying large information sets, called flip zooming. Flip zooming takes its inspiration from some of the previously developed focus+context methods, and addresses many of the problems associated with these. The idea behind flip zooming (Figure 1) is to break up a large data set, such as a document, into smaller segments, called pages. A page can be either in focus or out of focus. When a page is in focus, it is displayed at its normal, readable, size. But when out of focus, a page is reduced in size and displayed in some other way, e.g. as a thumbnail sketch. All pages are visible simultaneously, and users navigate by flipping through the pages in sequence, or by bringing a page into focus randomly by clicking on its small-size representation. When a page is zoomed into focus, either by flipping to it or clicking on its non-focus representation, it retains approximately the same position on the display, thus maintaining the contextual relationship to the rest of the material. The non-focus pages are dynamically re-arranged around the focus page, to maximize the use of the available display space. Flip zooming has several advantages over previous focus+context methods. It requires no complicated graphical transformations, which leads to a significantly better real-time performance. No spatial deformation of the material outside the focus takes place, which makes nonfocus information easier to read. Flip zooming allows for a variety of information to be displayed on those pages that are not in focus, including thumbnails, important keywords, a summary of the text on a page, or an icon. Finally, multiple foci, which are a problem with most focus+context views, would be easier to incorporate with flip zooming since there is less difficulty in determining how to display the area between two foci. Flip zooming can be useful in many situations when working with a large material, where access to both detailed information and a contextual overview is of importance. This material could include large documents, picture databases, collections of scanned documents, program code, and so on. The flip zoom technique might also be extended to included hierarchies of documents and other features to make the information display even more effective, such as the ability to “collapse” parts of a material into just one page, thereby freeing up more space on the display.
Figure 3. A flip zooming interface to a picture database
3. FLIP ZOOMING APPLICATIONS Flip zooming is a general approach to visualizing data sets. Here we present two sample applications of the technique: text browsing and picture browsing.
3.1. Text browsing As a first practical example of flip zooming we have developed The Zoom Browser (Figure 2). The Zoom Browser is a World Wide Web (WWW) browser which uses the flip zoom technique to visualize documents written according to the Hypertext Markup Language (HTML) standard. It is currently a text-only browser with limited HTML support, but it would be possible to extended it to include pictures and other features. When the Zoom Browser is first started, it displays a default HTML page. Users can then follow hypertext links or enter addresses to WWW-pages manually, as with any ordinary browser. Whenever a new document is loaded, it is split up into pages, and the new pages are added to the browser’s display. This means that the browser keeps a history of visited pages, any part of which is instantly available (pages can be removed if the display becomes cluttered). The Zoom Browser allows users to flip forwards and backwards through the pages on the display, or bring any page into focus by clicking on it. The Zoom Browser is written in the platform-independent language Java, which means that it can easily be incorporated with other web-based information services. This makes it possible to tightly integrate the Zoom Browser with a web site to give an effective presentation of a large material.
3.2. Browsing a picture database A second application area for the flip zoom technique is picture databases. Commonly, pictures that are made available on the Internet or on CD-ROM are accessible through thumbnail sketches. But the ability to work with full-sized pictures and thumbnails on the same display area is lacking, and users often lose the contextual overview when choosing to examine the full-size version of a picture.
Pictured (Figure 3) is an interface to a WWW-database of American road signs. Users are first presented with an overview of the material in the form of thumbnails. They can then select to see a full-size version of any of the available pictures, by clicking on its thumbnail representation. The selected picture is zoomed up to its original size, and surrounding pictures are suitably reduced. Users can then continue to select pictures by clicking on the thumbnails, or return to the original overview.
4. FUTURE WORK The next logical step for flip zooming would be an application that combined text and pictures in the same application, in the way that web-browsers display both text and pictures. Such a flip zooming-based tool might be used for accessing not only the WWW, but for instance on-line help manuals, which are currently hard to navigate. Another possible development would be to incorporate flip zooming with an interactive editing application, such as a word processor. This would give users an overview of an complete text while working on it, and might make it easier to interactively switch between different parts. It would also be possible to allow the editing of two or more documents side-by-side in the same window, which would allow for easier cutting and pasting between documents.
5. CONCLUSION Flip zooming is a general method for visualizing large amounts of text, images, or other data. So far, two applications utilizing the technique have been developed, but other applications are possible. We see flip zooming as a new possibility for overcoming the size limitations of today’s computer displays, and to present a large material in an effective way.
6. ACKNOWLEDGEMENTS Thanks to Johan Hagman for comments and corrections. This work was funded by the Swedish National Board for Industrial and Technical Development (NUTEK).
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