vid_get_square.py

import numpy as np
import cv2

cap = cv2.VideoCapture(0)
out = 0
while(1):
	ret, im = cap.read()
	imgray = cv2.cvtColor(im, cv2.COLOR_BGR2GRAY) # BGR to grayscale
	# imgray = cv2.GaussianBlur(imgray, (3, 3), 0)
	thresh = cv2.adaptiveThreshold(imgray,255,cv2.ADAPTIVE_THRESH_GAUSSIAN_C,\
            cv2.THRESH_BINARY_INV,35,12)
	# ret, thresh = cv2.threshold(imgray,90, 255, cv2.THRESH_BINARY_INV)

	contours, hierarchy = cv2.findContours(thresh, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE) # cv2.CHAIN_APPROX_NONE)

	rects = [cv2.boundingRect(ctr) for ctr in contours]


	max_area_rect = 0
	max_area_ctr = 0
	max_area = 0

	for ctr in contours:
		rect = cv2.boundingRect(ctr)

		if(rect[2]*rect[3] > max_area):
			max_area = rect[2]*rect[3]
			max_area_rect = rect
			max_area_ctr = ctr

	# cv2.rectangle(im, (max_area_rect[0], max_area_rect[1]), (max_area_rect[0] + max_area_rect[2], max_area_rect[1] + max_area_rect[3]), (0, 0, 255), 1)

	epsilon = 0.01 * cv2.arcLength(max_area_ctr, True)
	approx = cv2.approxPolyDP(max_area_ctr, epsilon, True)
	im = cv2.drawContours(im, [approx], -1, (0, 255, 0), 1)

	# im_rect =  im[max_area_rect[1]:max_area_rect[1]+max_area_rect[3], max_area_rect[0]:max_area_rect[0]+max_area_rect[2]]
	if(approx.shape[0] == 4):
		up_left = approx[0][0]
		up_right = approx[3][0]
		bottom_left = approx[1][0]
		bottom_right = approx[2][0]

		input_pts = np.float32([up_left,up_right,bottom_left,bottom_right])

		height = max(abs(bottom_left[1] - up_left[1]), abs(up_right[1]-bottom_right[1]))
		width = max(abs(bottom_left[0] - bottom_right[0]), abs(up_left[0]-up_right[0]))
		output_pts = np.float32([[0, 0], [width, 0],[0, height],[width, height]])

		# Compute the perspective transform M
		M = cv2.getPerspectiveTransform(input_pts, output_pts)
		 
		# Apply the perspective transformation to the image
		out = cv2.warpPerspective(im, M, (width, height), flags = cv2.INTER_LINEAR)
		cv2.imshow("out", out)
		# cv2.imwrite("out.png", out)

	# cv2.imshow("title", im)
	cv2.imshow("thresh", thresh)

	
	k = cv2.waitKey(30) & 0xff 
	if k == 27: # 27 is ascii code for ESC
		break


cap.release()
cv2.destroyAllWindows()