Iris Boundary Approximation Using Cosine Transform Series
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Solution Overview
Problem
Current iris recognition systems face challenges in accurately modeling and approximating the non-circular shape of the pupil and iris boundaries, especially when points on the boundary are not equally spaced, leading to inefficiencies in biometric identification.
Innovation Solution
A method using a least squares approximation by a cosine transform series as a function of angle about a fixed reference point to generate an approximate boundary representation, effectively handling irregularly spaced points and providing excellent pupil localization for both circular and non-circular pupils.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If standard Discrete Cosine Transform (DCT) methods are used to calculate coefficients, then the process is simple and efficient, but it cannot handle irregularly spaced points on the boundary
Solution Approach 1:
The patent transforms the problem by changing the parameter domain from uniform index-based spacing to angle-based spacing. By converting boundary points to polar coordinates (r, θ) and using angle as the independent variable, the method accommodates irregular radial spacing while maintaining a systematic representation framework. This parameter transformation enables the application of cosine transform series to irregularly spaced data points.
Solution Approach 2:
The patent introduces an angular dimension to the representation problem. Instead of directly representing boundary points in Cartesian coordinates with irregular spacing, the method maps points to a parameter space defined by angle θ and radius r. This dimensional transformation converts the irregular spacing problem into a manageable form where angular frequency analysis can be applied effectively.
2Measurement precision
If higher harmonics are used in the cosine transform series, then pupil localization accuracy is improved, but computational complexity increases
Solution Approach 1:
The patent applies partial action by using a finite number of harmonic terms (N) in the cosine transform series, where N is sufficient to achieve the desired localization accuracy but not necessarily the maximum possible. The method balances computational cost with accuracy requirements by selecting an appropriate truncation point for the series, avoiding unnecessary computation while maintaining adequate precision for biometric applications.
Data Source
AI summary
A method of approximating the inner or outer boundary of an iris comprises generating an approximate boundary representation (20) comprising a least squares approximation by a cosine transform series of a function of the angle (θ) about a fixed point (A) of the distance of measured points (10) on the boundary from the fixed point (A). More broadly, the method may be used to approximate the shape of any two-dimensional curve or figure.