3D Fingertip and Palm Tracking in Depth Image SequencesHui Liang, Junsong Yuan and Daniel Thalmann

Proceedings of the 20th ACM international conference on Multimedia 2012

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Outline• Introduction • Related Work• Proposed Method• Experimental Results• Conclusion

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Introduction

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Introduction• Human hand is an essential body part for human-computer

interaction.

• The positions of tracked fingertips: hand pose estimation

• Difficulty in fingertip tracking:

Side-by-side Bending Nearby

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Introduction• Many previous methods:

• Only focus on extracting 2D fingertips• Cannot track fingertips robustly for a freely moving hand

• In this paper:

• Present a robust fingertip and palm tracking scheme• With the input of depth images (KINECT)• Track the 3D fingertip positions quite accurately

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Related Work

Related work• Focus only on 2D fingertips:[4][5][6][9]

• Based on contour analysis of the extracted hand region:[2][4][5][6]

• Usually can track the fingertips for only stretched fingers.

Related work• In [6],

• Fingertips are tracked for infrared image sequences.• It utilizes a template matching strategy • Fingertip tracking : Kalman filter

• In [2],

• Stereoscopic vision is adopted• maximize the distance center of gravity of the hand & the boundary

Related work• In [9] (Kinect),

Depth < Threshold Circular filter

Minimum depth

Related work• [2] S. Consei1, S. Bourennane, and L. Martin. Three dimensional fingertip tracking in

stereovision, 2005. Proc. of the 7th Int’l Conf. on Advanced Concepts for Intelligent Vision Systems.

• [4] K. Hsiao, T. Chen, and S. Chien. Fast fingertip positioning by combining particle filtering with particle random diffusion, 2008. Proc. IEEE Int’l Conf. on Multimedia and Expo.

• [5] I. Katz, K. Gabayan, and H. Aghajan. A multi-touch surface using multiple cameras, 2007. Proc. of the 9th Int’l Conf. on Advanced concepts for intelligent vision systems.

• [6] K. Oka, Y. Sato, and H. Koike. Real-time tracking of multiple fingertips and gesture recognition for augmented desk interface systems, 2002. Proc. IEEE Int’l Conf. on Automatic Face and Gesture Recognition.

• [9] J. L. Raheja, A. Chaudhary, and K. Singal. Tracking of fingertips and centres of palm using kinect, 2011. Proc. Of the 3rd Int’l Conf. on Computational Intelligence, Modelling and Simulation.

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ProposedMethod

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Overview

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Hand and Palm Detection• 1) Assume the hand is the nearest object

• 2) Constrain global hand rotation by:

• : global rotation angle of the hand

ForegroundSegmentation

PalmLocalization

HandSegmentation

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• Threshold the depth frame to obtain the foreground F :

• p : a pixel coordinate • z(p) : depth value (of point p )• z0 : the minimum depth value

• zD : depth threshold

Hand and Palm DetectionForeground

SegmentationPalm

LocalizationHand

Segmentation

foreground F

0.2m

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• The palm region is approximated with a circle:

• pp : the palm center (of point p )

• rp : the radius

• Assume that hand palm forms a globally largest blob• Cp equals to the largest inscribed circle of the contour of F .• 2D Kalman filter : reduce computational complexity

Hand and Palm DetectionForeground

SegmentationPalm

LocalizationHand

Segmentation

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• Separate hand and forearm by a line:

• 1) Tangent to Cp

• 2) Perpendicular to the orientation of the forearm

• Orientation of the forearm :• The Eigenvector that corresponds to the largest

Eigenvalue of the covariance matrix of the contour pixel coordinates of F

Hand and Palm DetectionForeground

SegmentationPalm

LocalizationHand

Segmentation

Hand region : FV(2D) → FD(3D)

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Finger Detection and Tracking• Constraints on possible fingertip locations:

• 1) Only in depth discontinuous region ( in contour Fv)• 2) | Depth(one point) – Depth(neighborhoods) | are important.• 3) Utilize the 3D geodesic shortest path (GSP)

Fingertip vs. Non-fingertip

Nearby Fingertips

Initialization and Re-initialization

Fingertip Tracking

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Fingertip detectionFingertip tracking

• Goal: detect all five fingertips in the depth image• Based on three depth-based features

• Build a graph G :

• Vh : contains of all points within FV (hand contour)

• Eh : for each pair of vertices(p,q), 1) they are in the 8-neighborhood of each other 2) their 3D distance is within threshold τ

Fingertip Detection

Edge weight : 3D Euclidean distance

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• Calculate Geodesic distance dg(p):• From palm center pp for each vertex Vh

• Dijkstra graph search on Gh

• GSP point set Ug(p):• The set of vertices on the shortest path from pp to p

• Rectangle local feature RL(p):• Describe the neighborhood of a point p in FV

•

• : ratio of 1s

Fingertip Detection

0 0 11 1 1 1 11 1 X 1 01 1 1 1

0 1 0

Fingertip detectionFingertip tracking

1cm

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• Calculate Geodesic distance dg(p):

Fingertip Detection

0.4

Fingertip detectionFingertip tracking

dg(p)

𝜂(𝑝)

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• Fingertip labeling:

Fingertip Detection

:estimate the probability that has the label lj

number of GSP points frame number

1 2 3 4 5

1

2

3

4

5i : fingertip

j : label

Fingertip detectionFingertip tracking

Nmax=6

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• Fingertip labeling:

Fingertip DetectionFingertip detectionFingertip tracking

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Fingertip Tracking• Build a particle filter for each fingertip

• (x, ω) denote a particle• x : 2D position in FV • ω : the particle weight

• denote a particle

• Constrain the positions of each particle to the border point set UB to reduce the search space

Fingertip detectionFingertip tracking

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• Likelihood function :

•

Metric parameters

difference

Hausdorff difference

feature difference

Fingertip Tracking Fingertip detectionFingertip tracking

/

/

Geodesicdistance

GSP points

Neighbordepth

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Fingertip Tracking• Likelihood function :

Fingertip detectionFingertip tracking

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ExperimentalResults

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Experimental Results• Quantitative results on synthetic sequences:

Seq. No. Motion Seq.

No. Motion

Seq. 1 grasping Seq. 4 flexion

Seq. 2 adduction/abduction Seq. 5 global rotation

Seq. 3 successive single finger Seq. 6 combination of grasping and global rotation

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Experimental Results• Virtual object grasping:

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Conclusion

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Conclusion• Using multiple depth-based features for accurate fingertip

localization

• Adopting a particle filter to track the fingertips over successive frames

• Track the 3D positions of fingertips robustly

• Great potential for extension to other HCI applications