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OpenCV_Course_Note

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Preface

I have absolutely zero idea of the openCV library before watching this tutorial. I hope I can take away some useful knowledge by noting down some code here.

Reference

youtube
github

Reading Image and Video

Read Image

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import cv2 as cv

img = cv.imread('../Resources/Photos/cats.jpg')
cv.imshow('Cats', img)

cv.waitKey(0)

Read Video

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capture = cv.VideoCapture('../Resources/Videos/dog.mp4')

while True:
    isTrue, frame = capture.read()
    
    # if cv.waitKey(20) & 0xFF==ord('d'):
    # This is the preferred way - if `isTrue` is false (the frame could 
    # not be read, or we're at the end of the video), we immediately
    # break from the loop. 
    if isTrue:    
        cv.imshow('Video', frame)
        if cv.waitKey(20) & 0xFF==ord('d'):
            break            
    else:
        break

capture.release()
cv.destroyAllWindows()

Resizing and Rescaling

We often resize and rescale the image to relieve the computational strain.

Drawing Shapes and Putting Texts

5 Essential Function in OpenCV

  • Converting to grayScale
  • Blur
  • Edge Cascade
  • Dilating the image
  • Eroding
  • Resize

Converting to grayScale

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gray = cv.cvtColor(img, cv.COLOR2GRAY)

Blur

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blur = cv.GussianBlur(img, (7,7), cv.BORDER_DEFAULT)

Edge Cascade

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canny = cv.Canny(img, 125, 175,)
canny = cv.Canny(cv.GussianBlur(img, (7,7), cv.BORDER_DEFAULT, 125,175) # passing blur image

Dilating the image

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dilated = cv.dilated(canny, (3,3), iteration=1)

Eroding

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eroded = cv.erode(dilated, (3,3), iteration=3)

Resize

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resized = cv.resized(img, (500, 500), interpolation=cv.INTER_CUBIC)

Cropping

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cropped = img[50:200, 200:400]

Image Transformation

  • Translation
  • Rotation
  • Resizing
  • Flipping
  • Cropping

Contour detection