Build a Face Detection App with Python OOP — From Zero to Pro(part-1)

Part 1: Introduction & Project Architecture

Overview

This project implements a complete face detection + facial feature extraction pipeline using:

• YOLOv9-face for face bounding box detection
• MediaPipe FaceMesh for detailed landmark extraction (eyes, lips, etc.)
• A clean Object‑Oriented (OOP) architecture to keep everything modular, extensible, and production‑ready.

The tutorial explains everything in depth — what each class does, why it exists, and how all pieces work together.

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Why OOP for a CV project?

✔ Single Responsibility

Each class handles one job:

• Detecting faces
• Extracting features
• Rendering
• Managing models
• Running the main loop

✔ DRY Principles

Common functionality (image handling, webcam reading, etc.) lives in a single parent class: OpenCVBase.

✔ Scalability

Add a new model? New feature extractor? New rendering theme?

Just create a new class without touching existing ones.

✔ Performance

ConfigModel loads models once, preventing heavy repetitive initialization.

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Project Structure

project/
│
├── app/
│   ├── config_model.py
│   ├── opencv_base.py
│   ├── face_detector.py
│   ├── face_features_detector.py
│   ├── view.py
│   ├── face_app.py
│
├── model/
│   └── yolov9t-face-lindevs.pt
│
└── main.py

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Component Responsibilities

🔵 ConfigModel

Loads and caches models (YOLO, etc). Prevents loading multiple times.

🟢 OpenCVBase

Parent class that provides:

• self.img
• read_img()
• camera reading logic All detectors inherit from it.

🔴 FaceDetector

Uses YOLO to detect faces and returns bounding boxes.

🟣 FaceFeaturesDetector

Uses MediaPipe FaceMesh to extract:

• Left eye landmarks
• Right eye landmarks
• Outer lips
• Inner lips

🟡 View

Only responsible for drawing:

• Ellipses around faces
• Feature overlays
• Weighted blending
• Rendering with cv2.imshow

⚫ FaceApp

Main "application controller":

• Opens webcam (VideoCapture(0))
• Runs detection pipeline
• Sends results to View
• Handles exit logic
• Cleans up resources

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VideoCapture(0) — Why Zero?

0 represents the default webcam.

If you have multiple cameras:

• 0 → laptop camera
• 1 → USB webcam
• 2 → virtual camera

This project uses webcam input in both OpenCVBase and FaceApp.

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