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Our presentation on mobile interactive hologram verification at ISMAR 2013 in Adelaide, Australia ABSTRACT: Verification of paper documents is an important part of checking a person’s identity, authorization for access or simply establishing a trusted currency. Many documents such as passports or paper bills include holograms or other view-dependent elements that are difficult to forge and therefore are used to verify the genuineness of that document. View-dependent elements change their appearance based both on the viewing direction as well as dominant light sources, thus it requires special knowledge and training to accurately distinguish original elements from forgeries. We present an interactive application for mobile devices that integrates the recognition of the documents with the interactive verification of viewdependent elements. The system recognizes and tracks the paper document, provides user guidance for view alignment and presents a stored image of the element’s appearance depending on the current view of the document also recording user decisions. We describe how to model and capture the underlying spatially varying BRDF representation of view-dependent elements. Furthermore, we evaluate this approach within a user study and demonstrate that such a setup captures images that are recognizable and that can be correctly verified.
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Graz University of Technology
[email protected] ISMAR 2013
Mobile Interactive Hologram VerificationA. Hartl, J. Grubert, D. Schmalstieg, G. Reitmayr
Graz University of Technology
[email protected] ISMAR 2013
Motivation
View-Dependent Elements
Strong dependence on viewing angle/light sources
Security elements (e.g., holograms)
Often only a few distinct views
Color copies, substitutes etc.
Document Verification
ID-cards, passports, banknotes
Checking security elements
Several security levels
=> Level 1: check with a manual
Graz University of Technology
[email protected] ISMAR 2013
Contribution
Hologram Verification with Mobiles – Feasibility Check
Capturing hologram patches
View alignment/user guidance
Mobile AR prototype
Evaluation within user study
Revision of the prototype
Graz University of Technology
[email protected] ISMAR 2013
Hologram Capture
Assumption
Total radiance from a point on the hologram is dominated by a single light source
Fixed distance to surface
Dominant Light Source
LED light on mobile phone
Fixed to the camera with offset vector o: l ~ P + R . o
Representation
Spatially Varying BRDF
I=I(x,y,l,d); l,d as unit vectors; 2 DOF each
Þ6D appearance model per channel
High frequency representation for capturing sharp edges
required => use of texture, keeping warped patches
5D model; indexed by R and location x,y on the document
Graz University of Technology
[email protected] ISMAR 2013
View AlignmentObjective
Mobile method for alignment with a given 6 DOF pose
Reasonable accuracy despite mobile environment
Approach
Visual guidance with iron sights and a virtual horizon
Þ1 matching direction of the viewing ray
Þ2 position along the ray
Þ3 in-plane rotation
1
2
3
Graz University of Technology
[email protected] ISMAR 2013
Evaluation – User StudyQuestions
1. How accurate can the user acquire viewing directions with guidance?
2. Can the user verify a hologram with the proposed approach?
3. How would the approach compare with a digital manual?
4. Would it be feasible to build an automatic system?
Study – Hologram Verification Task
Wrapped 50 Euro banknotes; AR prototype vs. check with a manual
Controlled environment
Learning phase for both AR system and digital manual
No hints on similarity/dissimilarity
Participants could stop at any time
Decision on validity required
Participants
17 volunteers; 1 female
Little experience with holograms
Graz University of Technology
[email protected] ISMAR 2013
Maneuvering and Task PerformanceAlignment Error
Translation: -8mm-10mm
Rotation: -8 degrees - 8 degrees
Largest error with first view
Reasonable accuracy for non-experts.
Task Completion Times and Soundness
ÞNo difference in soundness
„I think, the hologram is real.“
ÞSignificant effect of interface on completion
time; higher temp. effort with AR system
ÞUsers were able to verify holograms
with both setups.
Graz University of Technology
[email protected] ISMAR 2013
Subjective Assessment
NASA TLX Weighted Scores
Workload assessment
ÞHigher physical/temporal demand
with AR system: users are forced
to move to the right pose
ÞNo clear evidence of either interface
on validity of the element
AttrakDiff Questionnaire
Measuring attractiveness, usability
Þlower usability for AR system
ÞHigher scores for hedonic dimensions
Graz University of Technology
[email protected] ISMAR 2013
Subjective Assessment and AutomationIMI (Intrinsic Motivation Inventory)
Measuring intrinsic motivation
ÞNo effect on value/usefulness
Significant effect on interest/enjoyment: higher motivation with AR
system
Patch Matching
Registration with optical flow
Normalized cross correlation (NCC)
4/6 views have NCC scores > 0.75
ÞRepeatable image capture of hologram patches
Graz University of Technology
[email protected] ISMAR 2013
Revised Prototype
Comments from User Study
Physical strain => automatic recapture during final alignment
Cognitive load => display of captured data, change of local decisions
Live-view; alignment ranges
Informal Study (7 Participants)
Comparison with previous iteration
ÞHigher confidence (5/7, 2 equal)
ÞEqual strain/effort (5/7, 2 less)
ÞLive-view and visual cues are useful (verbal)
ISMAR Demo Session
recorded patch
live-view
reference patch
Graz University of Technology
[email protected] ISMAR 2013
ConclusionFeasibility check for hologram verification on mobiles
Mobile SVBRDF image capture using dominant light source
User guidance approach using iron sights and the virtual horizon
Mobile AR prototype system
Evaluation in user study and comparison with digital manual
Findings
Capture of holograms and view alignment worked reasonably well.
Higher motivation to use the AR system, but it did not provide more value.
ÞHologram verification on mobiles seams feasible.
Future work
Evaluation of the revised prototype with substitutes or real fakes.
Crafting a less straining approach with dense matching.
Improving tracking robustness.
This work is supported by Bundesdruckerei GmbH.
Graz University of Technology
[email protected] ISMAR 2013
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