AFRL-SN-WP-TP-2003-101
`
`DOES ZOOMING IMPROVE IMAGE
`BROWSING?
`
`Tammara T.A. Combs
`Benjamin B. Bederson
`
`AUGUST 1999
`
`Approved for public release; distribution is unlimited.
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`©1999 ACM
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`4. TITLE AND SUBTITLE
`DOES ZOOMING IMPROVE IMAGE BROWSING?
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`6. AUTHOR(S)
`Tammara T.A. Combs
`Benjamin B. Bederson
`
`7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)
`University of Maryland
`Human-Computer Interaction Lab, Institute for Advanced Computer Studies
`Computer Science Department
`College Park, MD 20742
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`Published in the Proceedings of Digital Library (DL 99), pp. 130-137.
`1999 ACM. This work is copyrighted. The United States has for itself and others acting on its behalf an unlimited, paid-up,
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`14. ABSTRACT (Maximum 200 Words)
`We describe an image retrieval system we built based on a Zoomable User Interface (ZUI). We also discuss the design, results and
`analysis of a controlled experiment we performed on the browsing aspects of the system. The experiment resulted in a statistically
`significant difference in the interaction between number of images (25, 75, 225) and style of browser (2D, ZUI, 3D). The 2D and
`ZUI browser systems performed equally, and both performed better than the 3D systems.
`The image browsers tested during the experiment include Cerious Software’s Thumbs Plus, TriVista Technology’s Simple
`LandScape and Photo GoRound, and our Zoomable Image Browser based on Pad++.
`
`15. SUBJECT TERMS
`Evaluation, controlled experiment, image browsers, retrieval systems, real-time computer graphics, Zoomable User Interfaces
`(ZUIs), multiscale interfaces, Pad++
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`

`Does Zooming Improve Image Browsing?
`
`Tammara T.A. Combs and Benjamin B. Bederson
`Human-Computer Interaction Lab, Institute for Advanced Computer Studies
`Computer Science Department
`University of Maryland, College Park, MD 20742 USA
`+1 301 405-2764
`tcombs@cs.umd.edu, bederson@cs.umd.edu
`
`Sometimes pictures really are worth a thousand words, but
`what good are they if the interfaces do not offer the support
`that users need? In this paper we focus on the browsing
`aspect of the interface.
`Browsing is not a new concept. Webster’s New World
`Dictionary gives a basic definition of the term browse, to
`examine in a casual way. Adults browse for clothes on
`racks at their favorite department stores and children
`browse for sweets at their local candy shops. Vendors and
`department store owners have realized how to capitalize on
`sales. They know in order to maximize the purchase of
`their items, browsing needs to be made easy. Most
`storeowners understand that people will not select what
`they cannot see. For this reason, merchandise is usually
`displayed in a manner that best suits the targeted user.
`Why should image browsers be any different? Just as
`librarians shelve books to make them easier for patrons to
`find, image browsers should display images in such a way
`that does not distract the user from the main task he/she is
`trying to perform. For instance, if a user is browsing for an
`image to include in a document, their browsing experience
`should not be such that it has made him/her forget the
`reason they sought the image in the beginning.
`In image browsing, screen real estate is very important
`because it seems as if there is never enough. We believe
`3D and zooming make better use of screen space than
`scrolling. We describe our experiment and give some
`practical guidelines for future image browsers.
`In order to get a basis for understanding the context from
`which our system was designed, we offer the following
`definitions:
`
`1) An Image Retrieval (IR) System is an application that
`returns one or more images given some descriptive
`information. This information can be in the form of:
`a) An image,
`b) Keywords or phrases, or
`c) Natural language
`
`ABSTRACT
`We describe an image retrieval system we built based on a
`Zoomable User Interface (ZUI). We also discuss the
`design, results and analysis of a controlled experiment we
`performed on the browsing aspects of the system. The
`experiment resulted in a statistically significant difference
`in the interaction between number of images (25, 75, 225)
`and style of browser (2D, ZUI, 3D). The 2D and ZUI
`browser systems performed equally, and both performed
`better than the 3D systems.
`The image browsers tested during the experiment include
`Cerious Software’s Thumbs Plus, TriVista Technology’s
`Simple LandScape and Photo GoRound, and our Zoomable
`Image Browser based on Pad++.
`Keywords
`image browsers,
`Evaluation, controlled experiment,
`retrieval systems, real-time computer graphics, Zoomable
`User Interfaces (ZUIs), multiscale interfaces, Pad++.
`INTRODUCTION
`In the past two decades, with the emergence of faster
`computers, the declining cost of memory, the popularity of
`digital cameras, online archives and even presentation
`slides, the amount of stored graphical information has
`skyrocketed. Having the ability to store and manipulate
`images is becoming more important as images are being
`incorporated into electronic documents [12]. These digital
`images are stored and electronically encoded for future
`retrieval. Hence, there is a growing need for more
`sophisticated ways of retrieving and browsing images.
`However, the advances of these tools have not grown as
`rapidly as the needs of potential users.
`There is a vast diversity of users and individual biases that
`should be taken into consideration as we move toward
`multimedia systems. Graphical information is being used
`throughout many systems to help bridge the gap between
`such differences as languages, gender, age and personality.
`
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`DL 99, Berkeley, CA USA
`Copyright ACM 1999 1-58113-145-3/99/08 . . . $5.00
`
`130
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`2) An Image Browser is an application that allows users
`to select one or more images from multiple images.
`This browser has to:
`a) Be able to display multiple images at one time
`(possibly reduced resolution versions), and
`b) Support inspection of original full resolution
`versions of an image.
`
`The returned set of images (results) obtained from the
`Image Retrieval query may be displayed in an Image
`Browser for further refinement of the search by the user.
`Often it is the case that the results of the query yield more
`images than the user desires, so he/she has to browse. It is
`unfortunate that many query systems ignore browsing and
`just give the results of the query perhaps in the form of a
`list. This makes it hard and sometimes impossible for a
`user to select exactly what he/she needs. After testing the
`features in many of the browsers we decided to contribute
`to the image browser community and make our own
`browser – a zoomable image browser (ZIB) (See Figure 1).
`We designed ZIB where searching and browsing are tightly
`coupled. With ZIB, the images located in the browse area
`represent the results of the query posed in the search
`section. Both the search term and query results can be seen
`in one view.
`To begin our study we evaluated sixteen (16) image
`browsers (see Table 1). We compared and contrasted many
`features of the commercial and shareware products to
`discover some of the most popular techniques used in
`image browsers. We especially targeted software packages
`that were designed for the purpose of browsing a collection
`of images. To our surprise, most of the image browsers did
`not deviate from the typical two-dimensional grid of
`thumbnails approach. We chose ThumbsPlus (see Figure
`2) to be the commercial browser we would later use in the
`experiment because it is a good example of a commercial
`image browser. ThumbsPlus is a grid of thumbnails that is
`easy to use and supports access to the full-size image.
`
`Name of Package
`Corel Mosaic
`PhotoMagic
`PhotoCD Access
`GifDesk
`Fotoflood Image Manager
`Picture Publisher
`PhotoDisc
`Image AXS Pro
`ThumbsPlus
`ACDSee
`IrfanView32
`VPIC
`CompuPic
`Extensis Portfolio
`Cumulus
`PowerPoint
`
`Name of Company/Developer
`Corel Corporation
`MicroGrafx Corporation
`Eastman Kodak Company
`Jay Wherley
`EPICAD Design Incorporated
`Micrografx Incorporated
`PhotoDisc
`Digital Arts and Sciences
`Phillip Crews
`ACD Systems Unlimited
`Irfan Skiljan
`Bob Montgomery
`Photodex Corporation
`Extensis Corporation
`Canto Software
`Microsoft Corporation
`
`Table 1: List of systems analyzed
`
`System Design of the Zoomable Image Browser (ZIB)
`We designed a system that integrates image browsing and
`image retrieval. Query formulation is allowed within the
`search area. Users have the option of performing a simple
`or an advanced search. Within the simple search, Users
`have the option of entering one word or one phrase on
`which the query will be performed. Within the advanced
`search, the user may form a query by using a combination
`of words and/or phrases and Boolean connectives. The
`interface for the search area was written in TCL/TK and the
`search procedure was written in C++. Once query
`formulation is complete and the images which satisfy the
`query have been retrieved, the images are returned within
`the browse section.
`The results of the query appear in the lower (Browse)
`section and can be browsed by panning and zooming in and
`out of individual images as well as all images at once. The
`browse section was built using Pad++, a general purpose
`engine for writing zoomable user interface [2]. ZIB offers
`a unique advantage over many browsing systems in that the
`user has control of the tradeoff between the number of
`images displayed and the resolution of those images. For
`example, if ten images are present in the browse section
`and the user wants to hone in on four of the ten images,
`he/she can zoom in on the view and see the images enlarge
`before their eyes. This gives them higher resolution but
`fewer images. The inverse is also true. Users can zoom
`out to get lower resolution, but greater numbers of images.
`Users can also perform in-place zooming which allows
`them to see an image at full resolution located in the same
`place in the same scene.
`
`Search
`
`Query
`History
`
`Browse
`
`Figure 1: Zoomable Image Browser (ZIB)
`allows panning and zooming of individual
`images as well as the entire view.
`While users perform successive searches, a history
`interface maintains a record of previous queries and
`displays a snapshot of the images that were returned with a
`particular query. In case users forget the search terms used
`to retrieve the corresponding set of images, they need only
`move the mouse cursor over the group of images they wish
`
`131
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`3
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`5
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`A fourth, and particularly relevant study [11], is that of a
`group of students from the University of Maryland. The
`main focus of this study was to come up with an optimal
`tradeoff between image size and the number of images that
`could be displayed at once. They found that increasing the
`number of images while reducing their size resulted in
`reduced task completion time. However, they only tested a
`maximum of thirty-six (36) images. They concluded that
`further testing should be done with larger image sets, to
`determine what the optimal number of images viewed
`simultaneously are.
`EXPERIMENT
`We performed a user study to assess each of the browsing
`systems. We adopted the hypothesis that there would be no
`statistically significant differences in the time it took users
`to locate the targeted images, the browser users preferred,
`or in the number of incorrect selections made on a
`particular browser. This user study however did result in a
`statistical significance in each of these dependent variables,
`as we will discuss below.
`Equipment
`ThumbsPlus, Simple LandScape and PhotoGoRound are
`windows-based programs while
`the zoomable
`image
`browser runs on Linux. Because each subject evaluated all
`four browsers, we used two machines to avoid switching
`between operating systems on one machine. We were
`careful to eliminate any windows management tasks to
`avoid any differences is the two operating systems.
`Both of the computer systems used were 166 MHz Pentium
`PCs with 17” monitors. One system was running Windows
`NT 4.0 with a resolution of 1024 x 768, while the other
`system ran Linux with a resolution of 1280 x 1024.
`Because we wanted the machines to be of comparable
`speed, the Windows NT machine had 114 megabytes of
`RAM and the Linux machine had 64 megabytes of RAM.
`Browsing with the windows-based systems was performed
`using a 2-button mouse and browsing with the zoomable
`browser required the use of a 3-button mouse. We wrote a
`program that automated and recorded the questions and
`tasks presented to the subjects.
`Stimuli
`Each subject was asked to browse through a set of images
`until he/she had located the target image. They used
`browsing functionality specific to the browsing system the
`were working on at the time. For example, a user may have
`enabled autospin in the PhotoGoRound to complete the task
`of finding an image of strawberries as pictured below in
`Figure 5.
`Training
`Before beginning the experiment, each participant was
`educated in the use of image browsers in general. We
`wanted to be sure each subject had a clear understanding of
`the assignment they were about to perform. Subjects
`completed five pre-tasks using the first image browser that
`they would use. There was no time limit to the pre-tasks
`
`Figure 4: PhotoGoRound (P), a VRML image
`browser cretated by TriVista that uses a
`“lazy-susan” metaphor.
`
`The first study is the Zoom Browser [10] in which a web-
`browser
`(text-only) downloads HyperText Mark-up
`Language (HTML) documents from the World Wide Web
`(WWW) and splits them into thumbnails of pages. Users
`can navigate through the pages, clicking on links in the text
`to load new documents. There is also a sense of history
`keeping in that previously viewed documents remain
`visible. Users liked the overview achieved from the display
`of the pages in the Zoom Browser. However, the Zoom
`browser does not scale up well. Once a certain number of
`images is displayed on the page, the information displayed
`on the pages is no longer useful.
`In a second study, Protofoil [17], researchers built several
`information
`access
`applications where
`information
`(documents and text) was displayed as thumbnails in a grid.
`Users complained that they were not able to see the
`contents of the thumbnails clearly so the authors introduced
`intermediate page sizes allowing users to have a better
`detail view of the image. There was no concept of zooming
`used for this image browser.
`In a third study, the Pad++ group tested general navigation
`and history-related effectiveness using PadPrints [9], a
`WWW companion. PadPrints works along side a web
`browser to serve as a history aid building a hierarchy of
`pages visited by the user. The pages are displayed as
`thumbnails of images that also serve as links to the
`represented page. Users are permitted to view the entire
`graphical history or to zoom in to focus on the particular
`part of their history. Subjects were asked to navigate the
`Web with and without the zoomable web companion and
`for both of the tasks (textual and image-based pages), there
`were fewer pages accessed, and retrieval
`time was
`significantly reduced. This showed that some of the
`concepts used in PadPrints were effective in navigating.
`However, PadPrints serves as a web companion and it was
`not designed as a stand alone image browser. We used
`some of the same ideas from PadPrints in designing and
`developing the zoomable image browser. We presume that
`multiscale contextual display of the images can provide
`substantial support for browsing.
`
`133
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`6
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`

`

`and subjects were informed that they did not have to
`proceed with any further tasks until they felt comfortable
`with the browsing system. The goals of training were to
`verify
`that our subjects understood
`the navigation
`techniques for the browser and also to familiarize them
`with the program we used to automate the questions.
`
`Figure 5: Example image that subjects were
`asked to browse for during the experiment.
`Because training had already been administered to subjects
`on browsing and performance times were not being
`recorded, we did not repeat all of the previous techniques
`for training on the secondary browsers. Subjects were
`simply given the sheet of instructions before beginning the
`tasks associated with that browser and asked to read it and
`continue with the experiment when they were ready.
`Method
`The primary design of this experiment was a 3x4 block
`design. Each subject was given matched tasks for the four
`browsers. The independent variables were the different
`browsers (ThumbsPlus, Zoomable Image Browser, Simple
`LandScape, and PhotoGoRound) and number of images
`(25, 75, 225). The orderings of both independent variables
`were randomized.
`We conducted two experiments simultaneously. The first
`experiment used the method of between-subject testing.
`Each participant was randomly assigned one of the four
`browsers as their primary browser for use in this first
`experiment. Each user was instructed to browse through
`each of the three image sets. When the test user was ready,
`he/she would initiate a request for a new image. They
`would then return to the browser assigned to then and
`signify that they had found the correct image by selecting
`it. Browsing time for each of these images was recorded.
`The user repeated this process until the five images for each
`image set had been correctly selected. After each image set
`of five images, there was a small task to measure recall.
`Subjects were instructed to find an image they would like
`to send to a friend. Time was not recorded for this task.
`The purpose was to give subjects exploratory time as well
`as to observe how they would use the browser when there
`
`134
`5
`
`were no time constraints. Subjects were presented with
`four images to test recall. Subjects were instructed to select
`either “Yes, the image was in the set of images” or “No, I
`don’t recall seeing this particular image in the set.” They
`then evaluated their primary browser using a questionnaire
`and they were asked to give feedback on anything they felt
`wasn’t addressed during the experiment and they were also
`asked for any suggestions for improvement of the system.
`After the debriefing segment of each test user’s primary
`browser, they each began the second experiment, a with-in-
`subject test. With-in-subject design requires all the
`participants to use all of the systems that are being tested.
`Participants evaluated their secondary browsers in random
`order. In addition to the browsers being presented in
`random order, each participant only evaluated one of the
`three image sets. For example, one test user evaluated ZIB
`as her primary browser using the set of 25 images, then
`with 75 images, and then with 225 images. She then
`evaluated
`Simple LandScape with
`25
`images,
`PhotoGoRound with 25 images and ThumbsPlus with 25
`images. Just as the order for evaluation of the three image
`browsing systems was randomized, so were the image sets.
`Sixteen dependent variables were analyzed
`in
`the
`experiment. Mean performance time was measured for
`each of the three sets of images for the primary browser.
`Time to complete the task was calculated from the time that
`the subject initiated a request for a new question until they
`completed the task by selecting the targeted image. The
`number of incorrect selections was measured for the three
`image sets for the primary browser and the three secondary
`browsers. If an incorrect selection was made, subjects were
`instructed to continue searching until the correct image was
`found. A correct selection was eventually made 100% of
`the time. Percentage correctly recalled was measured for
`each of the three image sets for the primary browser. We
`calculated this by placing the total number correctly
`recalled over four (total number possibly correct).
`Lastly we measured mean subjective satisfaction ratings for
`each browser. We calculated these using questions from
`the Questionnaire for User Interaction Satisfaction (QUIS)
`developed at the University of Maryland [20] as well as
`questions specifically related to image browsing. All of the
`questions were based on the QUIS format and were
`therefore on a scale of one to nine.
`Subjects
`There were 30 participants involved in this experiment,
`most of whom were students at the University of Maryland,
`College Park with various backgrounds
`including
`Computer Science (45%), Electrical Engineering (20%),
`Graphic Design (10%) and Library Information Services
`(20%). Approximately 40% of the subjects were female
`and 60% of the subjects were male.
`Participants’ ages were recorded using ranges so they
`would not feel uncomfortable disclosing their ages. From
`the data we collected, 45% for the participants were
`
`7
`
`

`

`There were no significant ordering effect as it relates to
`user satisfaction for the primary browser (F3,25 = .745, p =
`.535). Also there were no significant differences in the
`browser test subjects preferred for the set of 75 images
`(F3,20 = 2.463, p = .092) or 225 images (F3,26 = 2.127, p =
`.121).
`
`13579
`
`User Satsifaction
`
`Thumbs+
`
`SLS
`ZIB
`Image Browser
`
`PGR
`
`Figure 8: Mean user satisfaction ratings for
`primary browsers averaged on all image
`sets.
`Subjects recalled images with 15% higher accuracy using
`ZIB compared with ThumbsPlus with our maximum
`number of images (see Figure 9).
`
`Thumbs+
`ZIB
`SLS
`PGR
`
`80
`
`70
`
`60
`
`50
`
`Task Type
`
`225
`75
`25
`Number of Images
`
`Figure 9: Average percentage of images
`correctly recalled.
`Also, there was a large number of incorrect selections
`(Figure 10) made
`for PhotoGoRound and Simple
`LandScape while relatively few were made for ThumbsPlus
`and ZIB.
`Analysis
`The results of this experiment showed that the zoomable
`image browser as well as the traditional 2D grid of
`thumbnails works best for performance time and user
`satisfaction. Users also made fewer incorrect selections for
`ZIB and ThumbsPlus. While the above statements are
`certainly true, we should note that all browsers did fairly
`well with performance time and recall with the small image
`set. With the maximum number of images, there was no
`preference
`toward ZIB, but ZIB had
`the
`fastest
`performance time.
`
`between the ages of 18 and 25, 40% between 26 and 35 and
`15% between 36 and 45. 97% of subjects reported they
`were experts on the World Wide Web (WWW) with the
`average user browsing 14 hours per week. Users also
`reported using a personal computer (PC) an average of 36
`hours per week.
`Each subject was paid $10 for participating in the
`experiment.
`Results
`We observed a statistically significant interaction effect
`between the browser and the number of images viewed
`with that browser for performance time. ZIB proved to be
`faster than the other browsers for each image set, although
`it was only significantly faster than Simple LandScape and
`PhotoGoRound (F2,18 = 12.359, p < .0005). Even with 225
`images, ZIB was not significantly faster than ThumbsPlus
`(See Figure 6). For an effect to be considered significant, p
`had to be less than or equal to 0.05.
`
`Thumbs+
`ZIB
`SLS
`PGR
`
`100
`80
`60
`40
`20
`0
`
`Time (Seconds)
`
`225
`75
`25
`Number of Images
`
`time per
`
`Figure 6: Mean performance
`browser for each image set.
`There was also a statistically significant interaction effect
`between browser and number of
`images
`for user
`satisfaction (see Figure 7). Again, ZIB had the highest user
`satisfaction ratings, but it was only significantly faster than
`Simple LandScape and PhotoGoRound (F3,29 = 15.667, p <
`.0005).
` ZIB was not significantly preferred over
`ThumbsPlus.
`
`Thumbs+
`ZIB
`SLS
`PGR
`
`13579
`
`User Satisfaction
`
`225
`75
`25
`Number of Images
`
`Figure 7: Mean user satisfaction ratings for
`all browsers.
`
`135
`6
`
`8
`
`

`

`Qualitative Results
`We gathered some qualitative results from our users as they
`performed the experiment. While many subjects said
`PhotoGoRound was the most entertaining, the most popular
`comment was that users did not like or wanted to change
`the speed of rotation. The Zoomable Image Browser,
`repeatedly said to be the easiest, received many comments
`suggesting the ability to group images in clusters by
`content. ThumbsPlus also received requests for an added
`vertical scroll bar, more accessible zooming, more images
`per page and the disappearance of the explorer window
`once their image set had been selected. The most sought
`after feature subjects wanted added
`to
`the Simple
`LandScape had to do with the overview. Users wanted
`some way to globally view places they had already visited
`in the landscape. Moreover, they wanted to see where they
`were presently in relation to the entire plane. Subjects
`repeatedly stated they were lost.
`We purposely left out searching tasks in this experiment.
`However, many subjects explicitly expressed a desire to
`search for the target image rather than browse for it.
`CONCLUSION
`While the current study shows some preliminary results,
`there are still several unanswered questions. For one, is
`there an optimal number of images that should be displayed
`on a screen at one time? If so, at what resolution should
`they be viewed? At what point will users feel a need to
`zoom in or out of their current view? Perhaps we should
`have had a fourth image set of 500 or more images, so that
`users would have had to zoom in order to see the contents
`of the images. Or perhaps we should have used a smaller
`window for the same reason.
`There are many unanswered questions, but from this
`experiment we have come up with some practical
`guidelines for designers of image browsing systems.
`Designers should choose approaches such as a zoomable
`image browser or 2D grid of thumbnails if they are
`concerned about the number of incorrect selections users
`make. The number of images displayed in the browser is
`also important. We saw in the results that there was a
`significant interaction effect between browsers and number
`of images. This means that designers should decided if
`their image browser is going to be used for large or small
`image sets. Either of the four aforementioned browsers are
`fine for relatively small numbers of images, but more
`traditional approaches or our zoomable image browser
`appear to work better when there is a large number of
`images.
`ACKNOWLEDGEMENTS
`We would first like to thank John Mareda and Ed Marek of
`TriVista for their input and support throughout this work.
`We give a special thanks to Norina Dixon who helped in
`the original implementation of ZIB. We thank all of our
`test users who so graciously participated in our experiment.
`We say thank you to the members of HCIL at UMD for
`their useful comments and accommodating spirits and also
`
`Thumbs+
`ZIB
`SLS
`PGR
`
`30
`25
`20
`15
`10
`
`05
`
`Number of Incorrect
`
`Selections
`
`225
`75
`25
`Number of Images
`
`incorrect
`
`Figure 10: Total number of
`selections made.
`Another peculiar observation we made was that roughly
`half of the subjects did not zoom when given 225 images in
`ZIB despite the fact that we gave training in zooming,
`However, there was still a performance time improvement.
`Perhaps it was because all the images were on one screen
`and they never had to adjust the view if they chose not to.
`We decided to maximize all browser screens to give the
`user maximum browsing space. However, this introduced a
`confounding variable because the 3D browsing systems
`used less screen space than the other two browsers did.
`This was due to the setup and design of the 3D systems,
`which was out of our control. Perhaps this is why
`performance time for the 3D systems was not as fast as the
`other browsers.
`Recall
`Test users had to do a substantial amount of scrolling in
`ThumbsPlus with 225 images. Perhaps this accounts for
`the 15% difference in recall compared to ZIB. Conceivably
`moving the scroll bar distracted them from the task and
`they were unable to remember the images that they had just
`stored in their short-term memory.
`Incorrect Selections
`A selection was considered incorrect when the user selected
`an image other than the target. Once an incorrect selection
`was made, the user continued to browse until the correct
`image was selected. Most incorrect selections were
`accumulated with
`the PhotoGoRound and Simple
`LandScape browsers. Perhaps this is due to the movement
`of the scenes. Users tried to select images from the
`PhotoGoRound while it was still spinning. Most of the
`time the result was the selection of an unwanted image. On
`the other hand, incorrect selections were relatively low in
`ThumbsPlus and ZIB. An observation that we made, as it
`relates to ZIB, is that as the number of images increased, so
`did the number of incorrect selections. Oddly enough, this
`was the only browser where there was a direct correlation
`between number of images and number of incorrect
`selections. An explanation we offer for this was gathered
`from observing the subjects. Despite having 225 images on
`the screen at one time, most users still did not zoom. They
`stayed zoomed out and thus could not see the images
`clearly.
`
`136
`7
`
`9
`
`

`

`11. Liebeskind, Andrew, North, Christopher, Orandi,
`Sharam, “Thumbnailing Techniques: Browsing Large
`Image Databases”, University of Maryland, College
`Park, December 1994
`http://www.cs.umd.edu/users/north/thumbnail.ps.Z.
`
`John Jones and Maya Venkatraman who helped with the
`analysis of the data. In addition, we acknowledge UNM
`and other members of the Pad++ team, especially Jim
`Hollan and Jon Meyer.
`The Zoomable Image Browser and Pad++ in general have
`been largely funded by DARPA to whom we are grateful.
`This study was funded by TriVista Corporation.
`REFERENCES
`1. Bederson, Benjamin, Hollan, James, “Pad++: A
`Zooming Graphical Interface for Exploring Alternate
`Interface Physics”, Proceedings of UIST’94 ACM
`Press, 17 – 26.
`2. Bederson, Benjamin, Hollan, James, Perlin, Ken,
`Meyer, Jon, Bacon David, and Furnas, George