pyfaceau 1.0.1

Pure Python OpenFace 2.2 AU extraction with CLNF landmark refinement

pyfaceau - Action Unit Generation based on Python and Openface 2.2

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Overview

pyfaceau is a Python reimplementation of the OpenFace 2.2 Facial Action Unit extraction pipeline. It achieves r =92 correlation with the original C++ implementation while requiring zero compilation and running on any platform.

Key Features

• ** 100% Python** - No C++ compilation required
• ** Easy Installation** - pip install and go
• ** High Accuracy** - r=0.92 overall
• ** High Performance** - 50-100 FPS with parallel processing (6-10x speedup!)
• ** Multi-Core Support** - Automatic parallelization across CPU cores
• ** Modular** - Use individual components independently
• ** 17 Action Units** - Full AU extraction (AU01, AU02, AU04, etc.)

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Quick Start

Installation

Option 1: Install from PyPI (Recommended)

# Install pyfaceau
pip install pyfaceau

# Download model weights (14MB)
python -m pyfaceau.download_weights

# Or manually download from GitHub
# https://github.com/johnwilsoniv/face-analysis/tree/main/S0%20PyfaceAU/weights

Option 2: Install from Source

# Clone repository
git clone https://github.com/johnwilsoniv/face-analysis.git
cd "face-analysis/S0 PyfaceAU"

# Install in development mode
pip install -e .

# Model weights are included in the repository

Basic Usage

High-Performance Mode (Recommended - 50-100 FPS)

from pyfaceau import ParallelAUPipeline

# Initialize parallel pipeline 
pipeline = ParallelAUPipeline(
    retinaface_model='weights/retinaface_mobilenet025_coreml.onnx',
    pfld_model='weights/pfld_cunjian.onnx',
    pdm_file='weights/In-the-wild_aligned_PDM_68.txt',
    au_models_dir='path/to/AU_predictors',
    triangulation_file='weights/tris_68_full.txt',
    num_workers=6,  # Adjust based on CPU cores
    batch_size=30
)

# Process video
results = pipeline.process_video(
    video_path='input.mp4',
    output_csv='results.csv'
)

print(f"Processed {len(results)} frames")
# Typical output: ~28-50 FPS depending on CPU cores

Standard Mode (4.6 FPS)

from pyfaceau import FullPythonAUPipeline

# Initialize standard pipeline
pipeline = FullPythonAUPipeline(
    retinaface_model='weights/retinaface_mobilenet025_coreml.onnx',
    pfld_model='weights/pfld_cunjian.onnx',
    pdm_file='weights/In-the-wild_aligned_PDM_68.txt',
    au_models_dir='path/to/AU_predictors',
    triangulation_file='weights/tris_68_full.txt',
    use_calc_params=True,
    use_coreml=True,  # macOS only
    verbose=False
)

# Process video
results = pipeline.process_video(
    video_path='input.mp4',
    output_csv='results.csv'
)

Example Output

frame,success,AU01_r,AU02_r,AU04_r,AU06_r,AU12_r,...
0,True,0.60,0.90,0.00,1.23,2.45,...
1,True,0.55,0.85,0.00,1.20,2.50,...

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Architecture

pyfaceau replicates the complete OpenFace 2.2 AU extraction pipeline:

Video Input
    ↓
Face Detection (RetinaFace ONNX)
    ↓
Landmark Detection (PFLD 68-point)
    ↓
3D Pose Estimation (Python Implementation of CalcParams with 98% fidelity)
    ↓
Face Alignment
    ↓
HOG Feature Extraction (PyFHOG)
    ↓
Geometric Features (PDM reconstruction)
    ↓
Running Median Tracking (Cython-optimized)
    ↓
AU Prediction (17 SVR models)
    ↓
Output: 17 AU intensities

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Custom Components & Innovations

pyfaceau includes several novel components that can be used independently in other projects:

Python-based CalcParams - 3D Pose Estimation

A pure Python implementation of OpenFace's CalcParams algorithm for 3D head pose estimation. Achieves 99.45% correlation with the C++ reference implementation.

from pyfaceau.alignment import CalcParams

# Initialize with PDM model
calc_params = CalcParams(pdm_file='weights/In-the-wild_aligned_PDM_68.txt')

# Estimate 3D pose from 2D landmarks
params_local, params_global, detected_landmarks = calc_params.estimate_pose(
    landmarks_2d,  # 68x2 array of detected landmarks
    img_width,
    img_height
)

# Extract pose parameters
tx, ty = params_global[4], params_global[5]  # Translation
rx, ry, rz = params_global[1:4]  # Rotation (radians)
scale = params_global[0]  # Scale factor

Use cases: Head pose tracking, gaze estimation, facial alignment

CLNF Landmark Refinement

Constrained Local Neural Fields (CLNF) refinement using SVR patch experts for improved landmark accuracy. Particularly effective for challenging poses and expressions.

from pyfaceau.detectors import CLNFRefiner

# Initialize refiner
refiner = CLNFRefiner(
    pdm_file='weights/In-the-wild_aligned_PDM_68.txt',
    patch_expert_file='weights/svr_patches_0.25_general.txt'
)

# Refine landmarks
refined_landmarks = refiner.refine_landmarks(
    frame,
    initial_landmarks,
    face_bbox,
    num_iterations=5
)

Use cases: Landmark tracking, facial feature extraction, expression analysis

Cython Histogram Median Tracker (260x speedup)

High-performance running median tracking for temporal smoothing of geometric features. Implements OpenFace's histogram-based median algorithm in optimized Cython.

from pyfaceau.features import HistogramMedianTracker

# Initialize tracker
tracker = HistogramMedianTracker(
    num_features=136,  # 68 landmarks x 2 (x,y)
    history_length=120
)

# Update with new frame
smoothed_features = tracker.update(current_features)

Use cases: Temporal smoothing, noise reduction, video feature tracking

Batched AU Predictor

Optimized AU prediction using batch processing for HOG features. Reduces overhead when processing multiple frames.

from pyfaceau.prediction import BatchedAUPredictor

# Initialize predictor
predictor = BatchedAUPredictor(
    au_models_dir='weights/AU_predictors',
    batch_size=30
)

# Predict AUs for multiple frames
au_results = predictor.predict_batch(
    hog_features_list,  # List of HOG feature arrays
    geom_features_list  # List of geometric feature arrays
)

Use cases: Video processing, batch AU extraction, real-time analysis

OpenFace22 Face Aligner

Pure Python implementation of OpenFace 2.2's face alignment algorithm. Produces pixel-perfect aligned faces matching the C++ implementation.

from pyfaceau.alignment import OpenFace22FaceAligner

# Initialize aligner
aligner = OpenFace22FaceAligner(
    pdm_file='weights/In-the-wild_aligned_PDM_68.txt',
    triangulation_file='weights/tris_68_full.txt'
)

# Align face for AU extraction
aligned_face = aligner.align_face(
    frame,
    landmarks_2d,
    tx, ty, rz  # From CalcParams
)

Output: 112x112 RGB aligned face, ready for HOG extraction

Use cases: Face normalization, AU extraction preprocessing, facial feature analysis

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Supported Action Units

pyfaceau extracts 17 Facial Action Units:

Dynamic AUs (11):

• AU01 - Inner Brow Raiser
• AU02 - Outer Brow Raiser
• AU05 - Upper Lid Raiser
• AU09 - Nose Wrinkler
• AU15 - Lip Corner Depressor
• AU17 - Chin Raiser
• AU20 - Lip Stretcher
• AU23 - Lip Tightener
• AU25 - Lips Part
• AU26 - Jaw Drop
• AU45 - Blink

Static AUs (6):

• AU04 - Brow Lowerer
• AU06 - Cheek Raiser
• AU07 - Lid Tightener
• AU10 - Upper Lip Raiser
• AU12 - Lip Corner Puller
• AU14 - Dimpler

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Requirements

Python Dependencies

python >= 3.10
numpy >= 1.20.0
opencv-python >= 4.5.0
pandas >= 1.3.0
scipy >= 1.7.0
onnxruntime >= 1.10.0
pyfhog >= 0.1.0

Model Files

Download OpenFace 2.2 AU predictor models:

• Available from: OpenFace repository
• Place in: AU_predictors/ directory
• Required: 17 .dat files (AU_1_dynamic_intensity_comb.dat, etc.)

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Project Structure

S0 pyfaceau/
├── pyfaceau/                  # Core library
│   ├── pipeline.py            # Full AU extraction pipeline
│   ├── detectors/             # Face and landmark detection
│   ├── alignment/             # Face alignment and pose estimation
│   ├── features/              # HOG and geometric features
│   ├── prediction/            # AU prediction and running median
│   └── utils/                 # Utilities and Cython extensions
├── weights/                   # Model weights
├── tests/                     # Test suite
├── examples/                  # Usage examples
└── docs/                      # Documentation

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Advanced Usage

Process Single Frame

from pyfaceau import FullPythonAUPipeline
import cv2

pipeline = FullPythonAUPipeline(...)

# Read frame
frame = cv2.imread('image.jpg')

# Process (requires landmarks and pose from CSV or detector)
aligned = pipeline.aligner.align_face(frame, landmarks, tx, ty, rz)
hog_features = pipeline.extract_hog(aligned)
aus = pipeline.predict_aus(hog_features, geom_features)

Use Individual Components

# Face detection only
from pyfaceau.detectors import ONNXRetinaFaceDetector
detector = ONNXRetinaFaceDetector('weights/retinaface_mobilenet025_coreml.onnx')
faces = detector.detect_faces(frame)

# Landmark detection only
from pyfaceau.detectors import CunjianPFLDDetector
landmarker = CunjianPFLDDetector('weights/pfld_cunjian.onnx')
landmarks, conf = landmarker.detect_landmarks(frame, bbox)

# Face alignment only
from pyfaceau.alignment import OpenFace22FaceAligner
aligner = OpenFace22FaceAligner('weights/In-the-wild_aligned_PDM_68.txt')
aligned = aligner.align_face(frame, landmarks, tx, ty, rz)

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Citation

If you use pyfaceau in your research, please cite:

@article{wilson2025splitface,
  title={A Split-Face Computer Vision/Machine Learning Assessment of Facial Paralysis Using Facial Action Units},
  author={Wilson IV, John and Rosenberg, Joshua and Gray, Mingyang L and Razavi, Christopher R},
  journal={Facial Plastic Surgery \& Aesthetic Medicine},
  year={2025},
  publisher={Mary Ann Liebert, Inc.}
}

Also cite the original OpenFace:

@inproceedings{baltrusaitis2018openface,
  title={OpenFace 2.0: Facial behavior analysis toolkit},
  author={Baltru{\v{s}}aitis, Tadas and Zadeh, Amir and Lim, Yao Chong and Morency, Louis-Philippe},
  booktitle={2018 13th IEEE International Conference on Automatic Face \& Gesture Recognition (FG 2018)},
  pages={59--66},
  year={2018},
  organization={IEEE}
}

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Acknowledgments

• OpenFace - Original C++ implementation by Tadas Baltrusaitis
• PyFHOG - HOG feature extraction library
• RetinaFace - Face detection model
• PFLD - Landmark detection by Cunjian Chen

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Support

• Issues: https://github.com/yourname/pyfaceau/issues
• Documentation: docs/
• Examples: examples/

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Built for the facial behavior research community