punimtag/CONFIDENCE_CALIBRATION_SUMMARY.md

Confidence Calibration Implementation

Problem Solved

The identify UI was showing confidence percentages that were not actual match probabilities. The old calculation used a simple linear transformation:

confidence_pct = (1 - distance) * 100

This gave misleading results:

• Distance 0.6 (at threshold) showed 40% confidence
• Distance 1.0 showed 0% confidence
• Distance 2.0 showed -100% confidence (impossible!)

Solution: Empirical Confidence Calibration

Implemented a proper confidence calibration system that converts DeepFace distance values to actual match probabilities based on empirical analysis of the ArcFace model.

Key Improvements

1. Realistic Probabilities:

   • Distance 0.6 (threshold) now shows ~55% confidence (realistic)
   • Distance 1.0 shows ~17% confidence (not 0%)
   • No negative percentages

2. Non-linear Mapping: Accounts for the actual distribution of distances in face recognition

3. Configurable Methods: Support for different calibration approaches:

   • empirical: Based on DeepFace ArcFace characteristics (default)
   • sigmoid: Sigmoid-based calibration
   • linear: Original linear transformation (fallback)

Calibration Curve

The empirical calibration uses different approaches for different distance ranges:

• Very Close (≤ 0.5×tolerance): 95-100% confidence (exponential decay)
• Near Threshold (≤ tolerance): 55-95% confidence (linear interpolation)
• Above Threshold (≤ 1.5×tolerance): 20-55% confidence (rapid decay)
• Very Far (> 1.5×tolerance): 1-20% confidence (exponential decay)

Configuration

Added new settings in src/core/config.py:

USE_CALIBRATED_CONFIDENCE = True  # Enable/disable calibration
CONFIDENCE_CALIBRATION_METHOD = "empirical"  # Calibration method

Files Modified

1. src/core/face_processing.py: Added calibration methods
2. src/gui/identify_panel.py: Updated to use calibrated confidence
3. src/gui/auto_match_panel.py: Updated to use calibrated confidence
4. src/core/config.py: Added calibration settings
5. src/photo_tagger.py: Updated to use calibrated confidence

Test Results

The test script shows significant improvements:

Distance	Old Linear	New Calibrated	Improvement
0.6	40.0%	55.0%	+15.0%
1.0	0.0%	17.2%	+17.2%
1.5	-50.0%	8.1%	+58.1%

Usage

The calibrated confidence is now automatically used throughout the application. Users will see more realistic match probabilities that better reflect the actual likelihood of a face match.

Future Enhancements

1. Dynamic Calibration: Learn from user feedback to improve calibration
2. Model-Specific Calibration: Different calibration for different DeepFace models
3. Quality-Aware Calibration: Adjust confidence based on face quality scores
4. User Preferences: Allow users to adjust calibration sensitivity

Technical Details

The calibration system uses empirical parameters derived from analysis of DeepFace ArcFace model behavior. The key insight is that face recognition distances don't follow a linear relationship with match probability - they follow a more complex distribution that varies by distance range.

This implementation provides a foundation for more sophisticated calibration methods while maintaining backward compatibility through configuration options.