How to find height and width for each individual contour on an image using OpenCV

Question

In the above image, if the entire width is specified say 30'5". How do I calculate height and width for each individual contour on that image using opencv

Answer 1

To obtain the height and width of a contour, you can use cv2.boundingRect. The function returns the contour information in the form of x,y,w,h. The height for a specific contour will be h and the width will be w. Here's the result with the w in pixels drawn onto the image.

import cv2

# Load image, convert to grayscale, Otsu's threshold
image = cv2.imread('1.jpg')
gray = cv2.cvtColor(image,cv2.COLOR_BGR2GRAY)
thresh = cv2.threshold(gray, 0, 255, cv2.THRESH_BINARY + cv2.THRESH_OTSU)[1]

# Find contours, obtain bounding rect, and draw width
cnts = cv2.findContours(thresh, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
cnts = cnts[0] if len(cnts) == 2 else cnts[1]
for c in cnts:
    x,y,w,h = cv2.boundingRect(c)
    cv2.putText(image, str(w), (x,y - 10), cv2.FONT_HERSHEY_SIMPLEX, 0.9, (36,255,12), 2)
    cv2.rectangle(image, (x, y), (x + w, y + h), (36,255,12), 1)

cv2.imshow('image', image)
cv2.waitKey()