id-scanner-lib/src/modules/face/comparator/comparator.ts

Browser-based ID card, QR code, and face recognition scanner with liveness detection

/**
 * @file Face Comparator
 * @description Face comparison using cosine similarity
 * @module modules/face/comparator
 */

import { FaceCompareResult, FaceDetectionResult } from '../detector/types';

export class FaceComparator {
  private _threshold: number = 0.6;

  constructor(threshold: number = 0.6) {
    this._threshold = threshold;
  }

  async compare(
    face1: FaceDetectionResult | number[],
    face2: FaceDetectionResult | number[]
  ): Promise<FaceCompareResult> {
    // Extract embedding
    const emb1 = Array.isArray(face1) ? face1 : face1.embedding ?? [];
    const emb2 = Array.isArray(face2) ? face2 : face2.embedding ?? [];

    // Compute cosine similarity
    const similarity = this._cosineSimilarity(emb1, emb2);

    return {
      similarity,
      isMatch: similarity >= this._threshold,
      threshold: this._threshold,
      algorithm: 'cosine-similarity',
    };
  }

  private _cosineSimilarity(a: number[], b: number[]): number {
    if (a.length !== b.length || a.length === 0) return 0;
    let dot = 0, magA = 0, magB = 0;
    for (let i = 0; i < a.length; i++) {
      dot += a[i] * b[i];
      magA += a[i] * a[i];
      magB += b[i] * b[i];
    }
    return dot / (Math.sqrt(magA) * Math.sqrt(magB));
  }
}