SHARING DIGITAL MEDIA ON COLLABORATIVE TABLES AND DISPLAYS TECHNICAL REPORT 602 TRENT APTED, JUDY KAY AND MARK ASSAD
NOVEMBER, 2006
Sharing Digital Media on Collaborative Tables and
Displays∗
Trent Apted,Judy Kay and Mark Assad
School of Information Technologies
University of Sydney
Sydney,Australia
{tapted,judy,massad}@it.usyd.edu.au
November13,2006
Abstract
This paper describes the design and early experience with Cruiser–a multi-user,gestural,collaborative digital photograph sharing interface for a
tabletop–and the techniques we use to share information with devices and
other displays in its pervasive computing environment.The design is strongly
influenced by the metaphor of physical photographs placed on the table and
we have concentrated on the provision of an effective UbiComp interface that
does not use a keyboard,a mouse or traditional WIMP(Windows,Icon,
Mouse,Pointer)interface widgets.That is,with an emphasis on seamlessness.
Aspects of the interface include the ability to interactively attach audio,
handwriting or drawings,as well as other photographs to the“back”of an
image afterflipping it over;direct sharing of images with digital cameras,large
displays and other UbiComp devices;and the provision of personal spaces–
an area close to a user in which only they can work,which is enforced by the
interface.
1Introduction
We are just beginning to explore the possibilities afforded by tabletop interfaces, including the provision of some interactions that are not well supported by traditional computer displays.Face-to-face collaboration is possible,with multiple users sitting around the tabletop,each able to access computing resources.A table involves a social dimension and an environment where users can interact with a computer and each other in an informal setting.A tabletop also has the natural concept of a user’s personal space–an area close to them in which they can work.
The need for technology to support natural tabletop interaction has prompted researchers to approach the hardware problem from a number of directions.Here, the problem is the determination of where each user is acting on the display.Devices such as the DiamondTouch[3]use capacitive coupling with the human body to detect multiple touches,while computer vision techniques are used in other work[7, 9]with varying results.There is also the possibility of adapting mature technologies ∗Appeared at“The Spaces In-between:Seamful vs Seamless Interactions”workshop held in conjunction with The Seventh International Conference on Ubiquitous Computing(UbiComp 2005),11September,2005,Tokyo,Japan.
This work was conducted as part of the Homes&Communities project,a joint project between the University of Sydney and the Smart Internet CRC.
Figure1:Cruiser in use
such as SMARTBoards[5]or Mimio[10],traditionally for vertical presentation whiteboards),to support multiple users on a large horizontal surface. Furthermore,collaborative touch technology and computer vision techniques are still at an early stage and it is attractive to explore these,stylus-based alternatives especially as a pen is particularly natural for some interactions.
Regardless of the hardware chosen,there is a need to explore software possibil-ities to support natural interaction.Early work with touch screens introduced the concept of a gesture for manipulating virtual objects without a mouse or keyboard [6].More recently,and closest to our work,Shen et al.[8]investigate layout techniques for multi-user browsing of photo libraries and story sharing on a circular tabletop in their Personal Digital Historian(PDH).Our work introduces novel annotation methods and attempts to provide an interface truer to the analogy of physical photographs lying a table for collaborative mark-up and social interaction.
In this paper,we will outline our techniques for interacting with the tabletop,as well as with other devices in the environment through the tabletop interface.These currently include a wall-sized stereosc
opic display,digital still cameras,regular computing desktops and a prototype“magic mirror”distributed home messaging system we are developing.We will also discuss methods for handling input from these devices;as well as a microphone,the display framebuffer itself and multiple users in a manner that enforces ownership and privacy on the tabletop.
2Overview of Cruiser
Our work is motivated by the desire to support,for digital photographs,natural archival and mark-up activities with groups of people,and the social interaction experienced while sharing photographs.This was once accomplished by passing the latest pile of holiday snaps back from the developer around a coffee table, but the advent of digital photography is changing the nature of photography and
the photographic process.While this transition brings with it many possibilities
Figure2:The projected image for4users
:The blackhole(an image partially within it)
:An image photo corner(selected by‘cyan’user)
:A dynamically updated remote framebuffer“photo”from a laptop
:An audio object,attached to the back of a“Keep-in-Touch”image
(audio objects on people are synchronised with the magic mirror interface) :The Frame; :Aflipped photo with attachments(some writing)
in terms of copying,editing,publishing and printing,it also brings challenges in terms of presentation,viewing and sharing photographs[4],which our work is investigating.
We use pen-based gestures for manipulating digital photographs on a tabletop interface,and leverage modern dedicated computer graphics hardware to efficiently simulate a physical tabletop with photographs placed on it.These may be annotated,manipulated and shared using a pen.Hardware is not the focus of this work,so we have adapted the Mimio system,an off-the-shelf whiteboard capture tool,to support asynchronous multi-user pen-based interaction.However, the application is not bound to this hardware.In fact an earlier version[1]used a DiamondTouch for input.The C++and OpenGL implem
entation is tested on Windows,Mac OSX and Linux to ease future adaptation.
Cruiser supports use by up to four users at the tabletop through the configu-ration of a static layout.Figure1shows the layout for two users,with the two participants sitting opposite each other.Each participant has a coloured triangular “personal space”in front of them.Figure2shows the user view for three or four users.A photo selected by a particular user has a border and photo-corner indicated  and also shown on the images in Figure3.Other objects,such as the Black Hole  ,remote framebuffer photo ,audio objects and Keep-in-Touch images ,the Frame and writing are described below.
2.1General Interface Concepts
After selecting a photo by physically touching it with a pen tip,it can be
moved by sliding the tip over the tabletop.We attempt to maintain the physical-
2
Figure3:The rotate/resize gesture
The centre of the image remainsfixed while the image rotates and resizes to keep the“ ”under
a user’sfinger
virtual coupling throughout this and other actions,by keeping the contact point on the photo appear“stuck”to the pen tip.This coupling is broken in special circumstances–the centre of the photo is not allowed to move offscreen,nor is it allowed to enter another user’s personal space.
To rotate and resize a photo,a user mustfirst touch it in a photo corner. The photo is rotated and resized concurrently,with the centre of the photofixed and the contact point remaining under the pen as it moves in two dimensions.For example,Figure3(a)shows the contact point moving from position1,inwards and in an anti-clockwise direction to end at position2,giving the superimposed version of the photo;reduced in size and rotated45◦.Figure3(b)shows an enlargement and170◦rotation.
Toflip a photo,a user selects a triangle along one of the photo’s edges and drags it across to the opposite edge.Again,we wish to keep the original point under the pen tip,so this occurs gradually and i
n simulated3D.If other photos are beneath it,the user will see theflipping photo pass through those images,as its plane rotates on a horizontal axis through the centre of the photo,parallel to the edge whose triangle was chosen.Onceflipped,the user sees a partially transparent white surface and they may attach other objects on the table to that image,which will be automatically laid out on theflipside.This is done simply by moving the object over aflipped image and releasing.resized
A photo may also beflicked,during a move action.This occurs when a photo (or other movable object)is released whilst it is moving with a velocity greater than a threshold–currently300pixels per second.The object is given momentum and subjected to a kinetic frictional force that causes it to decelerate.This action becomes relevant when the table is large and a user might not be able to reach across the full width to pass a photograph to another user,but it can also be a trigger for other actions and events.The photo is stopped if any user selects(“grabs”)it,and it is not allowed to fall offthe edge of the table,nor move into the personal space of a user other than that of the user whoflicked it.
In the current implementation,users may send a photograph from the tabletop to a wall-sized display,where it is shown covering the wall,for wider presentation and analysis.This occurs at the edge of the table closest to the display,so the user simplyflicks the image towards the display itself.In our lab,the display is a
“3D DataWall”that allows the display of stereoscopic photographs,and a three-dimensional animation of the photograph moving from the edge of the table to the wall.The latter is a design towards seamlessness,but the need for3D goggles to see the effect(and their unsuitability for interaction with the current tabletop) means that it is usually wasted.Flicking to the opposite edge of the table currently inserts the image into a slideshow on the magic mirror interfaces,which behave like
a dynamic picture frame when not in use.
2.2Special Actions
A user may copy a photo by an implicit action that is triggered when they try to move an unowned photo into their personal space.A copy owned by that user is created once the original would have been moved more than a threshold distance into the personal space and the copy immediately becomes the user’s active selection, which they are still moving.
To draw or write,a user simply uses the pen on the background.That is,they do not select a photo,but drag the pen over the black,public area or their own personal space.This mode switch is implicit,so we take steps to avoid accidental drawings.
To attach audio to a photo,a user dwells on that photo.They are prompted to record their audio and repeat the dwell when they arefinished speaking.A circular audio object is created that is automatically attached to the back of that image and numbered.To replay the audio,a user dwells on the audio object(afterflipping the image if necessary).This enables a user to attach one or more pieces of audio to a photo,for example as an annotation or a message.
2.3Special Objects and Places
Personal space objects are coloured triangular elements drawn on the display, which demarcate the exclusive area for each user.For example,once the centre point of a photo is contained within a user’s personal space,no other user may select that photo.This enforces a range of social conventions surrounding what constitutes acceptable behaviour for items in public space versus one’s personal or private space.
The Black Hole is a semi-translucent photo with swirls.It can be manipulated as a typical photo(moved,rotated,resized,etc.)but is never obscured by other photos and cannot be copied or moved into a personal space–it is a shared resource. The Black Hole has a“sphere of influence”that affects the size of other photos near or in it.Figure4shows a user moving a photo into the Black Hole.M
oving from the right to left,the photo gets smaller as it moves closer to the centre until it is hidden.This occurs as the touch point(indicated by a“ ”),rather than the photo centre is moved closer to the centre of the Black Hole.This gives the photo an appearance of being gradually“sucked”into the Black Hole.
The Black Hole is our take on the trash can.As the Black Hole is moved,photos in its sphere of influence move with it.Photos may be retrieved by either reducing the size of the Black Hole(allowing partially hidden photos on the fringes to be retrieved)or by dragging the Black Hole into your personal space.In the latter case,the Black Hole itself does not move into your personal space,but photos that are unowned or owned by you1will“fall out”,into your personal space.Dwelling on the Black Hole causes photos already within it to be permanently deleted,and all other movable photos to slowly move towards the Black Hole.This can be used 1Thus a user may“delete”a photo they own by moving it into the Black Hole and other users may not remove it

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