Transcript
Page 1: Wearable Eye Tracker

Wearable Eye Tracker

Xiaoyong YeFranz  Alexander Van Horenbeke

David Abbott

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IndexIntroductionBackgroundHardwareSoftware

System DesignAlgorithm

Pupil Localization Ellipse Fitting Calibration Homographic Mapping

Experimental ResultsFuture Work

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IntroductionA complete system able to track the user’s

eye and map the position of their pupil with the area at which they are looking at in the scene in front of them

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BackgroundWearable Eye-Tracking information

Who has done previous workWhat they have used

Recent Methods used with eye tracker

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ObjectivesHardware

WearableLow-CostLight and

ConfortableMoveable eye-

camera

SoftwareReal-TimeAccurate

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HardwareHead-Mounted GearTwo Cameras:

Scene CameraEye Camera

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HardwareScene Camera

Captures the scene in front of the user

Fixed to the head

Eye CameraCaptures the eyeWith 5 DOF with

respect to the head

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System DesignEye Image Scene Image

Pupil Localization

Ellipse Fitting

Calibration Done?

Mapping

Marker Detection

Calculate Homograp

hy

No

Yes

Ellipse Center

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Pupil LocalizationAutomatic Threshold (Modified Otsu’s

Method)

Image Morphology(Dilation, Erosion)

Connected Components Analysis(Find Pupil)

Pupil Center Estimation

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Histogram of an Eye Image

Graylevel

Pupil

Background

Threshold

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Pupil Localization Threshold

Erosion

Connect Component

s

Pupil Detection

Dilation

Fill holes

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Ellipse Fitting1. Updating the pupil Center

2. Need 5 points for Fitting Ellipse model

3. RANSAC to deal with noisy points

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Ellipse FittingRANSAC method

Edge Image

Starburst Algorithm

Feature Points

RANSAC

Ellipse Fitting

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CalibrationRelationship between Ellipse center to

Scene Image

*=

Scene Position

Homography Pupil Center

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Solving for homographies

8 degrees of freedom in 3 x 3 matrix H, so at least n = 8 pairs of points are sufficient to determine it

Set up a system of linear equations:Ah = 0

where vector of unknowns h = [a,b,c,d,e,f,g,h]T

Need at least 8 eqs, but the more the better…

Solve for h. solve using least-squares

1yx

ihgfedcba

wwy'wx'

X’ = Hx

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calibration method

1. Look at Scene Marker and Press corresponding number on keyboard,

2. Each marker press 2 to 3 times.

3. Randomly select 8 pairs of points to calculate Homography.(Repeatly)

3. Choose the best Homography matrix.

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Mapping

(x1, y1)

(x2, y2)

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Experimental ResultsFrame rate 25/second

Accurate Pupil Ellipse

Mapping error is low( 13 pixels in 640*480 image)

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Future WorkHardware

Lighter camerasScene camera position

Software

Use corneal refletionTry different mapping techniques

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Thank you!


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