object-detection.py

''' This script detects a object of specified object colour from the webcam video feed.
Using OpenCV library for vision tasks and HSV color space for detecting object of given specific color.'''

#Import necessary modules
import cv2
import imutils
import numpy as np
from collections import deque
import time
import math

#Define HSV colour range for green colour objects
greenLower = (29, 86, 6)
greenUpper = (64, 255, 255)

#Used in deque structure to store no. of given buffer points
buffer = 20

#Points deque structure storing 'buffer' no. of object coordinates
pts = deque(maxlen = buffer)

#Start video capture
video_capture = cv2.VideoCapture(0)

#Sleep for 2 seconds to let camera initialize properly.
time.sleep(2)

#Loop until OpenCV window is not closed
while True:
    #Store the readed frame in frame, ret defines return value
    ret, frame = video_capture.read()
    #Flip the frame to avoid mirroring effect
    frame = cv2.flip(frame,1)
    #Resize the given frame to a 600*600 window
    frame = imutils.resize(frame, width = 600)
    #Blur the frame using Gaussian Filter of kernel size 5, to remove excessivve noise
    blurred_frame = cv2.GaussianBlur(frame, (5,5), 0)
    #Convert the frame to HSV, as HSV allow better segmentation.
    hsv_converted_frame = cv2.cvtColor(blurred_frame, cv2.COLOR_BGR2HSV)

    #Create a mask for the frame, showing green values
    mask = cv2.inRange(hsv_converted_frame, greenLower, greenUpper)
    #Erode the masked output to delete small white dots present in the masked image
    mask = cv2.erode(mask, None, iterations = 2)
    #Dilate the resultant image to restore our target
    mask = cv2.dilate(mask, None, iterations = 2)

    #Display the masked output in a different window
    cv2.imshow('Masked Output', mask)

    #Find all contours in the masked image
    _,cnts,_ = cv2.findContours(mask.copy(), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

    #Define center of the ball to be detected as None
    center = None

    #If any object is detected, then only proceed
    if(len(cnts)) > 0:
        #Find the contour with maximum area
        c = max(cnts, key = cv2.contourArea)
        #Find the center of the circle, and its radius of the largest detected contour.
        ((x,y), radius) = cv2.minEnclosingCircle(c)

        #Calculate the centroid of the ball, as we need to draw a circle around it.
        M = cv2.moments(c)
        center = (int(M['m10'] / M['m00']), int(M['m01'] / M['m00']))

        #Proceed only if a ball of considerable size is detected
        if radius > 10:
            #Draw circles around the object as well as its centre
            cv2.circle(frame, (int(x), int(y)), int(radius), (0,255,255), 2)
            cv2.circle(frame, center, 5, (0,255,255), -1)

        #Append the detected object in the frame to pts deque structure
        pts.appendleft(center)

        #This function makes the trailing line behind the detected object
        for i in range(1, len(pts)):
            if pts[i-1] is None or pts[i] is None:
                continue

            thickness = int(np.sqrt(buffer / float(i + 1)) * 2.5)
            cv2.line(frame, pts[i - 1], pts[i], (0, 0, 255), thickness)

    #Show the output frame
    cv2.imshow('Frame', frame)
    key = cv2.waitKey(1) & 0xFF

    #If q is pressed, close the window
    if(key == ord('q')):
        break
#After all the processing, release webcam and destroy all windows
video_capture.release()
cv2.destroyAllWindows()