Score components in SourceAFIS transparency data

Detailed scoring, a part of algorithm transparency, is a breakdown of similarity score that is computed by SourceAFIS during matching for a pair of fingerprints. Scoring is done separately for every pairing. Pairing with the highest total score is selected as the best match.

Format

Scoring is recorded as a CBOR-encoded object holding several fields. Final similarity score is stored in shapedScore field. Other fields describe intermediate scores that contribute to the final score.

• minutiaCount - Number of matched minutiae, regardless of correctness of minutia type or accuracy of angles and distances.
• minutiaScore - Score assigned for minutiaCount.
• minutiaFractionInProbe - Fraction of probe minutiae that were successfully paired, including approximate matches like in minutiaCount.
• minutiaFractionInCandidate - Like minutiaFractionInProbe but for candidate minutiae.
• minutiaFraction - Average of minutiaFractionInProbe and minutiaFractionInCandidate.
• minutiaFractionScore - Score assigned for minutiaFraction.
• supportingEdgeSum - Number of supporting edges in the pairing graph.
• edgeCount - Number of edges in the pairing graph, including supporting edges. This value is actually one higher than that.
• edgeScore - Score assigned for edgeCount.
• supportedMinutiaCount - Number of minutiae with at least one supporting edge in addition to edges in the pairing tree.
• supportedMinutiaScore - Score assigned for supportedMinutiaCount.
• minutiaTypeHits - Number of matched minutia pairs where probe and candidate minutia have the same type (ending or bifurcation).
• minutiaTypeScore - Score assigned for minutiaTypeHits.
• distanceErrorSum - Sum of distance errors, i.e. differences between probe and candidate edge length, for all edges in the pairing tree.
• distanceAccuracySum - Like distanceErrorSum but zero at maximum tolerated distance error and increasing towards exact match.
• distanceAccuracyScore - Score derived from distanceAccuracySum and distanceErrorSum.
• angleErrorSum - Sum of angle errors, i.e. differences between probe and candidate edge angles that are measured between reference/neighbor minutia direction and edge direction, for all edges in the pairing tree.
• angleAccuracySum - Like angleErrorSum but zero at maximum tolerated angle error and increasing towards exact match.
• angleAccuracyScore - Score derived from angleAccuracySum and angleErrorSum.
• totalScore - Total raw score computed by adding together above score components.
• shapedScore - Final similarity score computed from totalScore with the help of monotonic shaping function constructed in such a way as to make shapedScore approximately correspond to FMR (false match rate) thresholds. Increase in shapedScore by 10 points roughly corresponds to 10x lower FMR.

Example: 047-score.cbor

{
  "minutiaCount": 29,
  "minutiaScore": 0.928,
  "minutiaFractionInProbe": 0.6170212765957447,
  "minutiaFractionInCandidate": 0.7435897435897436,
  "minutiaFraction": 0.6803055100927442,
  "minutiaFractionScore": 6.109143480632843,
  "supportingEdgeSum": 270,
  "edgeCount": 299,
  "edgeScore": 79.235,
  "supportedMinutiaCount": 29,
  "supportedMinutiaScore": 5.597,
  "minutiaTypeHits": 26,
  "minutiaTypeScore": 16.354,
  "distanceErrorSum": 253,
  "distanceAccuracySum": 111,
  "distanceAccuracyScore": 3.0189560439560443,
  "angleErrorSum": 4.476240332317074,
  "angleAccuracySum": 5.297603478851171,
  "angleAccuracyScore": 1.5122314200586873,
  "totalScore": 112.75433094464756,
  "shapedScore": 225.6584429542732
}