UMR 5205

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Virtual arm for the Phantom Limb Pain Therapy

Eynard L. and Meyer A. and Bouakaz S.

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The Phantom Pain

Pain or discomfort felt by an amputee in the area of the missing limb

Why? Physical Amputation ≠ Psychic amputation Mismatching between brain and reality → Pain

CharacteristicsStrong pain, sometimes debilitatingHard to treat

Existing therapiesMedics, massage, relaxation, psychotherapiesNew hopeful therapies …

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News methods for therapy

[Ramachadran96] Cognitive Science Institute ISC Lyon [Sirigu03]

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Our idea

Computer Science Posture Tracking (vision) Augmented reality: virtual limb

Our system Camera Posture analysis Augmented picture of missing limb Mirror screen

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Presentation summary

Previous Works

Our contributionReal-Time Posture AnalysisThe mirror effect : Virtual arm

Results

Conclusion

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Movements Tracking (vision)

Multi-camerasVoxelic reconstruction [Mikic03,…] 3D-model : recognition of the skeleton a 3d-grid

Monocular (1 camera)Optical flow Bayesian methods [Agarwal04,…]Real-Time [Stenger03,…]

Limited movementSmall resolution

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Our system constraints

Ours constraints Real-Time (Interactivity) Monocular (portative system)

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Presentation summary

Previous Works

Our contributionReal-Time Posture Analysis

Background substraction Precomputation: anthropometric measures Posture Tracking

Mirror effect : Virtual arm

Results

Conclusion

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Background substraction

Learning-based algorithm N frames → RGB values extrema for each pixel Connexity search → noise reduction

Simple and fast

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Precomputation: anthropometric measures

Anthropometric values computation Needed for the tracking

2 postures

Silhouette extraction

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Head and Torso measurements

Pose 1: head measure Highest  pixel in silhouette

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Head and Torso measurements

Pose 1: head measure Highest pixel in silhouette Going down into the image while Nbi(whitepixel)> Nbi-1(whitepixel)

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Head and Torso measurements

Pose 1: head measure« highest » pixel in frameGoing down on the image while Nbi(whitepixel)>Nbi-1(whitepixel)

→ Head widthGoing down until Nb(whitepixel) < threshold* width

→ Shoulder line

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Head and torso measurements

Torso measure Barycenter line → Torso width Going down until separation → bottom of the torso

→ Torso height

widthheight

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Arm measurements

Pose 1Level and side of the amputation

Each arms sizes

Horizontal extreme points

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Arm measurements (2)

Pose 2

lbrachium

H

h /2elbow

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Presentation summary

Previous Works

Our contributionReal-Time Posture Analysis

Background substraction Precomputation: anthropometric measures Posture Tracking

Mirror effect : Virtual arm

Results

Conclusion

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Head and Torso detection

Head and TorsoConnexity research algorithm helped by the

anthropometrics measures

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Seek articulations

Seeking shoulder, elbow and wrist

Anthropometrics measurements → estimation of the positions

S

Sv

v~

E~

E

Forearmaxis

P1P2

C1

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Missing limb creation

If before-elbow amputationCoordinates systems of valid and amputee side are equivalentReprojection of pixels valid side → amputee side

Sv S

a

Xs

Ys

Xa

Ya

A s

A a

copy

Ov

Oa

Ev

W

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Virtual arm creation

If below-elbow amputationCoordinates system of valid and amputee side are equivalentReprojection of pixels valid side → amputee side

Sv S

a

XsYs

a

Ya

A s

Aa

copy

Ov

Oa

Ev

W

Ea

X

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Results

Webcam (640*480)

About 8 to 10 frames / s

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Remarks

Up Follow-up the side-displacements of the silhouette Whole image reflecting Better illusion for subject Interactive time

ConstrainsSubject must be facing the cameraFor a better illusion the elbows angles have to be

symmetricNon Snake moves

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Conclusion and future works

Experimental systemSimple posture trackingConstrains but robustVirtual arm creation

Next stepExperiment on amputeeCollaboration with ISC of Lyon

Perspectives 3D-model to be more realistic Amputees reactions to real experiments

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Thank you …

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Ajout du membre → réalité augmentée (RA)

Problème générique en RA

Cohérence entre réel et virtuel Texture, aspect

Élément de synthèse construit à partir d’image réelle (cf notre système)

Illumination, Ombre

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Creation du membre manquant

amputation huméralecentre de gravité du moignon obtention d'un axe grâce a al même méthode que pour le

bras valideamputation cubitaleMême méthode que pour le bras valideObtention de l'axe du moignon grâce au centre de gravité

de la partie après le coude

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hhead

htorsolLarm

whead

w

lRarm

yneck

ypelvis

xmin

xmax

xRshoulder

xLshoulder

torso

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