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ValueError: too many values to unpack (expected 2)

shruti A
shruti A asked
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Last Modified: 2017-11-28
ValueError: too many values to unpack (expected 2) this error occured when executing below program
# USAGE
# python distance_to_camera.py

# import the necessary packages
import numpy as np
import cv2

def find_marker(image):
	# convert the image to grayscale, blur it, and detect edges
	gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
	gray = cv2.GaussianBlur(gray, (5, 5), 0)
	edged = cv2.Canny(gray, 35, 125)

	# find the contours in the edged image and keep the largest one;
	# we'll assume that this is our piece of paper in the image
	(cnts, _) = cv2.findContours(edged.copy(), cv2.RETR_LIST, cv2.CHAIN_APPROX_SIMPLE)
	c = max(cnts, key = cv2.contourArea)

	# compute the bounding box of the of the paper region and return it
	return cv2.minAreaRect(c)

def distance_to_camera(knownWidth, focalLength, perWidth):
	# compute and return the distance from the maker to the camera
	return (knownWidth * focalLength) / perWidth

# initialize the known distance from the camera to the object, which
# in this case is 24 inches
KNOWN_DISTANCE = 24.0

# initialize the known object width, which in this case, the piece of
# paper is 12 inches wide
KNOWN_WIDTH = 11.0

# initialize the list of images that we'll be using
IMAGE_PATHS = ["images/2ft.png", "images/3ft.png", "images/4ft.png"]

# load the furst image that contains an object that is KNOWN TO BE 2 feet
# from our camera, then find the paper marker in the image, and initialize
# the focal length
image = cv2.imread(IMAGE_PATHS[0])
marker = find_marker(image)
focalLength = (marker[1][0] * KNOWN_DISTANCE) / KNOWN_WIDTH

# loop over the images
for imagePath in IMAGE_PATHS:
	# load the image, find the marker in the image, then compute the
	# distance to the marker from the camera
	image = cv2.imread(imagePath)
	marker = find_marker(image)
	inches = distance_to_camera(KNOWN_WIDTH, focalLength, marker[1][0])

	# draw a bounding box around the image and display it
	box = np.int0(cv2.cv.BoxPoints(marker))
	cv2.drawContours(image, [box], -1, (0, 255, 0), 2)
	cv2.putText(image, "%.2fft" % (inches / 12),
		(image.shape[1] - 200, image.shape[0] - 20), cv2.FONT_HERSHEY_SIMPLEX,
		2.0, (0, 255, 0), 3)
	cv2.imshow("image", image)
	cv2.waitKey(0)
 

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error came like this

Traceback (most recent call last):
  File "C:\Users\vip\AppData\Local\Programs\Python\Python36-32\distance-to-camera\distance_to_camera.py", line 41, in <module>
    marker = find_marker(image)
  File "C:\Users\vip\AppData\Local\Programs\Python\Python36-32\distance-to-camera\distance_to_camera.py", line 16, in find_marker
    (cnts, _) = cv2.findContours(edged.copy(), cv2.RETR_LIST, cv2.CHAIN_APPROX_SIMPLE)
ValueError: too many values to unpack (expected 2)
>>> 

so what i need to do to execute it correctly
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