Rubber-Sheet Model
Definition
The coordinate transform that maps the annular iris region (between pupillary and limbic circles) to a normalised rectangular strip of fixed dimensions, making the IrisCode invariant to pupil dilation and image distance.
- Function
- Maps annular iris region to a rectangular strip
- Bounds mapped
- Pupillary and limbic circles
- Purpose
- Normalises for pupil dilation and image distance
- Used in
- Daugman IrisCode algorithm
Common questions
Why is normalisation needed before iris features are encoded?+
The pupil constantly changes size and images are captured at varying distances, so without a common coordinate system the same iris would produce different raw feature patterns on different occasions, making comparison unreliable.
What happens if the pupillary or limbic boundary is detected inaccurately?+
An inaccurate boundary distorts the rubber-sheet mapping, shifting where iris texture lands in the normalised strip, which can reduce match accuracy or increase false non-matches even for the same eye.
Related terms
- DOD ABIS
- US Department of Defense Automated Biometric Identification System, administered by the Defense Forensics and Biometrics Agency, holding iris, fingerprint, face and DNA...
- Hamming Distance (HD)
- The fraction of bit positions where two IrisCodes disagree, computed only over mutually unmasked bits. Genuine pairs centre around HD 0.10-0.15; impostor...
- HIIDE
- Hand-held Interagency Identity Detection Equipment: a handheld iris and fingerprint capture device used by US military forces in Iraq and Afghanistan for...
- Integro-Differential Operator
- Daugman's boundary-detection method: it maximises the magnitude of the line-integral intensity gradient around circular paths, locating the pupillary and limbic boundaries of...
- IrisCode
- The 2048-bit binary template produced by quantising the phase of 2D Gabor wavelet responses across the normalised iris strip. Phase encoding provides...
- NIST IREX
- NIST Iris Exchange: the series of iris recognition algorithm evaluations conducted by the National Institute of Standards and Technology since 2009, providing...
- Puttaswamy V. Union of India (2018)
- Supreme Court of India judgment upholding Aadhaar's constitutional validity while classifying iris and other biometric data as sensitive personal information within the...
- UIDAI
- Unique Identification Authority of India, the statutory body created by the Aadhaar Act 2016 that operates the world's largest biometric identity system,...
- Usable Bit Fraction
- The proportion of IrisCode bits not masked for eyelid, eyelash, or specular reflection occlusion. Values below 0.7 reduce match confidence; values below...