Usable Bit Fraction
Definition
The proportion of IrisCode bits not masked for eyelid, eyelash, or specular reflection occlusion. Values below 0.7 reduce match confidence; values below 0.5 are typically considered unreliable for forensic use.
- Field
- Iris recognition biometrics
- Measures
- Proportion of IrisCode bits not masked by occlusion
- Reliable threshold
- Below 0.7 reduces match confidence
- Unreliable threshold
- Below 0.5 typically unusable
Common questions
What commonly causes a low usable bit fraction?+
Eyelid droop, eyelash occlusion, off-axis gaze, and specular reflections from glasses or contact lenses all mask segments of the iris, reducing the count of bits available for comparison.
How does a low usable bit fraction affect a forensic match decision?+
Comparisons rely on the fractional Hamming distance computed only over unmasked bits, so a low usable fraction shrinks the statistical basis for the score and analysts flag such comparisons as lower confidence or inconclusive rather than a firm match or exclusion.
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...
- Rubber-Sheet Model
- The coordinate transform that maps the annular iris region (between pupillary and limbic circles) to a normalised rectangular strip of fixed dimensions,...
- UIDAI
- Unique Identification Authority of India, the statutory body created by the Aadhaar Act 2016 that operates the world's largest biometric identity system,...