Elliptical Pupil Estimation for Partially Obscured Eye Tracking
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Solution Overview
Problem
Conventional eye movement measurement devices underestimate pupil diameter and inaccurately determine center positions when the pupil is partially hidden, and commercially available devices cannot detect iris information due to eyelid coverage, leading to unreliable vertical and horizontal position information.
Innovation Solution
An eye information estimate apparatus that calculates the position and size of a pupil or iris by acquiring coordinates and slope information from an image, assuming an elliptical shape, using coordinates of two points on a predetermined line and tangent line slopes to determine the ellipse's major and minor axes, center coordinates, and rotation angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If circle fitting is applied to detected pupil edge points to measure pupil diameter and center position, then the measurement process is simple, but the pupil diameter is underestimated in half-blinking state and the center position shifts when the pupil is partially hidden
Solution Approach 1:
The patent segments the pupil detection process into multiple steps: first detecting the pupil edge points, then fitting an ellipse rather than a circle. This segmentation allows the system to handle partial occlusion by using the elliptical model which can accommodate hidden portions, thereby improving measurement accuracy while maintaining process simplicity.
Solution Approach 2:
The patent changes the geometric parameter from circular symmetry to elliptical symmetry. By assuming the pupil follows an elliptical shape rather than a perfect circle, the system can accurately measure pupil diameter and center position even when partially hidden, as the ellipse parameters (major axis, minor axis, orientation) provide more degrees of freedom to fit the visible portion.
2Measurement precision
If the entire pupil must be included in the captured image for accurate measurement, then measurement accuracy is maintained, but the device cannot capture images when the pupil is partially hidden by eyelids or other obstructions
Solution Approach 1:
The patent applies partial action by detecting and fitting the ellipse to only the visible portion of the pupil edge points. Rather than requiring the entire pupil to be visible, the system uses the detected edge points that are visible in the image to fit an elliptical model, which can then extrapolate the complete pupil parameters even when partially hidden.
3Loss of information
If iris detection is attempted when upper and lower sides of the iris are covered by eyelids, then iris information can be obtained, but conventional methods cannot detect the iris due to the coverage
Solution Approach 1:
The patent performs preliminary detection of the pupil center and uses this information to guide the iris detection process. By first establishing the pupil center position and then scanning horizontally from this reference point, the system can detect the iris edge even when vertically obscured by eyelids, as the horizontal scan avoids the vertically blocked regions.
4Ease of manufacture
If the center position of the iris is found by scanning horizontally with reference to the pupil center, then the detection process is simplified, but position information in the vertical direction is not reliable and horizontal accuracy is lost when centers vertically shift
Solution Approach 1:
The patent transitions from a one-dimensional horizontal scan to a two-dimensional elliptical fitting approach. By fitting an ellipse to the detected iris edge points and deriving the center position from the ellipse parameters, the system simultaneously obtains accurate horizontal and vertical center coordinates, eliminating the reliability issues of vertical positioning while maintaining process efficiency.
Data Source
AI summary
A technology capable of estimating information on a position and a size of a pupil or an iris using an image obtained by photographing eyes of a subject even when a part of the pupil or the iris is hidden in the image is provided. An eye information estimate apparatus includes a profile determination information acquisition unit configured to acquire, from an image obtained by photographing an eye of a subject, coordinates (x1, y0) and (x2, y0) of two points of a point P1 and a point P2 respectively corresponding to an outer edge of a pupil or an iris on a predetermined line included in the image and, in a case when a shape of the pupil or the iris is assumed to be an ellipse, slopes θ1 and θ2 of tangent lines of the ellipse at the point P1 and the point P2 respectively from the image, and an eye information calculation unit configured to calculate, R being set a length of a major axis of the ellipse, center coordinates (xc, yc) and an angle of rotation ψ of the ellipse representing a position of the pupil or the iris, and/or a length Rb of a minor axis of the ellipse representing a size of the pupil or the iris using the coordinates (x1, y0) and (x2, y0) of the point P1 and the point P2 respectively, the slopes θ1 and θ2 of the tangent lines of the ellipse at the point P1 and the point P2 respectively, and the length R of the major axis of the ellipse.