Color Object Tracking with OpenCV

Color tracking is fairly a simple activity in OpenCV and you may find a variety of articles in the Internet which describe different mechanisms and implementations. However the common steps involve the following.

  1. Convert the source frame into HSV color space.
  2. Define the upper bounds and lower bounds for the color you intend to track. In my example I mind the blue color and so the lower bound and upper bounds are respectively (100, 150, 0) and (140,255, 255) where the lower bound being the darker blue.
  3. Find the image mask that contain pixels which fall within the lower and upper bounds as mentioned above.
  4. Find contours in the mask image.
  5. Find the maximum contour in terms of the contour area. So that we can omit trivial contours and focus only on the most dominating blue color object in the scene.
  6. Approximate the maximum contour into a polygon.
  7. Find the bounding rectangle of the above polygon.
  8. Draw the rectangle from above step on the source image.

The code that follows the above series of steps is provided below.

#This is an exercise to track blue color from camera.

import numpy as np
import cv2

cap = cv2.VideoCapture(0)
while(True):
ret, source = cap.read()
if(not ret):
print('Error in video capture')
break
hsv = cv2.cvtColor(source, cv2.COLOR_BGR2HSV)
lowerblue = np.array([100,150,0])
upperblue = np.array([140,255,255])
mask = cv2.inRange(hsv, lowerblue, upperblue)

#find contours in the mask
im, contours, hierarchy = cv2.findContours(mask, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

maxContour = max(contours, key=cv2.contourArea)
epsilon = 0.1*cv2.arcLength(maxContour, True)
approxpoly = cv2.approxPolyDP(maxContour, epsilon, True)
x,y,w,h = cv2.boundingRect(approxpoly)
cv2.rectangle(source,(x,y),(x+w, y+h),(0,255,0), 2)
cv2.imshow('original', source)

if (cv2.waitKey(1) & 0xFF == 113):
break

cap.release()
cv2.destroyAllWindows()

The demonstration is shown below.

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