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Virtual Rear Projection: Technology & Evaluation

Jay Summet

summetj@cc.gatech.edu

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Introduction

Jay Summet - PhD student, Georgia Institute of Technology

Co-Advised: Gregory Abowd (HCI / Ubicomp) & Jim Rehg (Computer Vision)

Other work:

– Tracking and Projecting on handheld displays (Pervasive2005, UIST 2005),

– Detecting camera phones and blinding them (Ubicomp 2005)

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Virtual Rear Projection Using multiple redundant front projectors to

emulate the experience of a rear projected

surface.

• Introduction

• Motivation for VRP

• Initial Technology Development

•User Evaluation• More Technology Development

• Future Work

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Rear Projection

• No shadows!

• But extra costs...– Display Material

– Installation

– Space cost (77$ sq. ft.)

– Immobile

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Larger Board = Higher Cost

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Front Projection

• Inexpensive:– Display Screen

– Installation

– Mobility

• Effective use of space.

• But shadows & blinding light are annoying!

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Shadows

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Blinding Light

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Warped Front Projection (WFP)

• Moves shadow away from directly in front of the user.

• Commercial products using WFP:

– NEC WT600

– 3M IdeaBoard

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WFP Measurements

3379 166

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Passive VRP (PVRP)

• Overlapped projectors fill in shadows.

• Calibration via camera or manually.

• Projective transforms done on graphics card.

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Passive VRP Measurements

2509 167

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Movie (part 1)

Demo Movie of WFP/PVRP

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Benefits of Redundant Illumination

One Projector (WFP) Two Projectors (PVRP)

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Research Questions

•Are shadows / blinding light a problem?– Very little research with interactive

surfaces performed using front projection.

– But no real research into the effects of shadows on users of interactive surfaces.

• Is Passive VRP “good enough”?

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Projection Technologies Studied

Front Projection Virtual Rear Projection

Warped Front Projection Rear Projection

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Participants

17 Participants– Undergraduate students

– Mean age: 21.3 Std. Dev 1.77

– 9 males, 8 females

– Exclusively right handed

– Normal or corrected-to-normal vision

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Task

Box Task– 8 starting positions

– Target in Center

Dependent Variables– Acquire time

– Total Time

– Number of occluded boxes

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Results (1/3)

Subjective:– Users found projected light annoying

– Users had clear technology preferences:FP, WFP < VRP < RP

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Results (2/3)

Quantitative:– Box Acquire Time Slower:

FP < WFP, VRP < RP

– Less Boxes OccludedFP – 178 WFP – 66 VRP – 4 RP – 0

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Results (3/3)

Behavioral:– Users adopted coping behaviors to deal with

shadows in the FP and WFP conditions

– Not present in the VRP and RP conditions

• Edge of Screen – 7

• Near Center – 7

• Move on Occlusion – 3

• Dead Reckoning - 1

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Movie

Participant Video Figure

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Edge of Screen (7 participants)

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Near Center (7 participants)

Participants would stand in the center and...– ...either be short enough so that they would

not occlude boxes. (3 participants)

– ...or they would sway their bodies to find occluded boxes. (4 participants)

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Move on Occlusion (3 participants)

These participants would move whenever they occluded a box, and stay there until they occluded another.

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Findings (CHI 05)

• Users prefer Rear Projected and Passive Virtual Rear Projected displays over the others.

• RP and passive VRP eliminated coping behaviors seen in FP and WFP.

• Users find projected light to be annoying.

• Passive VRP casts light on users.

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Projected light is a larger problem as you add more projectors.

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Technology DevelopmentShadow Elimination – CVPR '01

– R. Sukthankar, T.-J. Cham, G. Sukthankar

– U. Kentucky – C. Jaynes, Visualization 2001

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Shadow Elimination Measurements

1052 221

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Technology DevelopmentBlinding Light Suppression – CVPR '03

– Tat Jen. Cham, Jim Rehg, Rahul Sukthankar,Gita Sukthankar

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SE + BLS Measurements

1165 34

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Interesting, but useless

•Required an unoccluded view of the screen, too slow.

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Technology Development

Switching – PROCAMS '03

– Ramsaroop Sommani

GPU Enhancements – PROCAMS '05

– Matt Flagg

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Active Virtual Rear Projection

• Detects occluders, turns off pixels they are occluding, and fills in those pixels with alternate projectors

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Active VRP Measurements

1466 12

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Movie (part 2)

Active VRP

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Future Work

User evaluation of Active VRP– Controlled laboratory study (80 participants)

– Exploratory Research

• AeroSpace Engineering Design Lab

• “Home-Office” in Aware Home

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More information:summetj@cc.gatech.edu

http://www.cc.gatech.edu/cpl/vrphttp://www.cc.gatech.edu/cpl/

procams

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Thank you!

The End

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Table of Relative Performance