OpenCV in Python Tutorial Series

Introduction to OpenCV

• OpenCV: Open source computer vision library used for image and video analysis, processing, and manipulation.
• Common uses: Image loading, drawing, facial detection, recognition, object detection, object tracking.
• Target audience: Python users; no need for extensive machine learning knowledge.
• Content scope: Basics to advanced techniques over multiple videos.

Installing OpenCV

• Requirements: Python, PIP (PIP3 for Mac/Linux).
• Install commands:
  • pip install opencv-python
  • Alternatives if PIP doesn’t work:
    • python -m pip install opencv-python
    • python3 -m pip install opencv-python
• Note: OpenCV may automatically install NumPy.

Setting Up the Project

• Create a project folder, e.g., opencv_tutorial.
• Inside the folder:
  • Create a Python file, e.g., tutorial1.py.
  • Create an assets folder containing images and videos.
• Use a code editor (e.g., Sublime Text).

Basic Image Operations

1. Import OpenCV: import cv2 as cv (Note: cv2 is used instead of opencv-python).
2. Load an Image:
   • Image path: path/to/image.jpg.
   • Use modes:
     • Default (Color): cv.IMREAD_COLOR or -1
     • Grayscale: cv.IMREAD_GRAYSCALE or 0
     • Unchanged: cv.IMREAD_UNCHANGED or 1
   • Example: img = cv.imread('assets/logo.jpg', cv.IMREAD_GRAYSCALE)
3. Display an Image:
   • Show Image: cv.imshow('Window Name', img)
   • Wait for Key: cv.waitKey(0) (0 means wait indefinitely until a key is pressed).
   • Close Windows: cv.destroyAllWindows()

Image Manipulation

1. Resize an Image:
   • Using fixed dimensions: resized_img = cv.resize(img, (400, 400))
   • Using scale factors: resized_img = cv.resize(img, (0, 0), fx=0.5, fy=0.5)
2. Rotate an Image:
   • Clockwise 90°: rotated_img = cv.rotate(img, cv.ROTATE_90_CLOCKWISE)
   • Counter-clockwise 90°: rotated_img = cv.rotate(img, cv.ROTATE_90_COUNTERCLOCKWISE)

Writing an Image

• Save an Image: cv.imwrite('new_image.jpg', img)
• Example output folder management: A new file new_image.jpg will be created in the same directory.

Summary

• Covered basics: loading, displaying, resizing, rotating, and saving images using OpenCV.
• Next steps: Move towards more advanced image and video manipulations in future tutorials.

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