Build a Face Detection App with Python OOP — From Zero to Pro(part-3)

Part 3: OpenCVBase — Designing a Clean Parent Class

Why Create a Base Class?

Both FaceDetector and FaceFeaturesDetector must:

• Receive an image (self.img)
• Read images from webcam or file
• Validate input
• Provide helper utilities

Instead of duplicating code, we put common logic in OpenCVBase.

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Core Responsibilities of OpenCVBase

✔ Input management

Keeps self.img consistent across all detectors.

✔ Camera handling

Implements read_img() which reads from:

• webcam
• image path

✔ Error handling

Ensures detectors never receive invalid images.

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Example Implementation

class OpenCVBase:
    def __init__(self):
        self.img = None

    def read_img(self, source=0):
        import cv2

        cap = cv2.VideoCapture(source)
        success, frame = cap.read()
        cap.release()

        if success:
            self.img = frame
            return frame
        return None

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Why 0 is Default Again?

Because the default webcam is usually device index 0.

This ensures that if the user runs the app without arguments, it "just works."

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Benefits of Using OpenCVBase

✔ DRY (Don’t Repeat Yourself)

Only one place to manage images.

✔ Consistent API

All detectors expect the same .img.

✔ Easy to extend

If you add preprocessing later (resize, normalization), you only add it here.

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