Want to find contours -> ValueError: not enough values to unpack (expected 3, got 2), this appears
PythonPython 3.xOpencv ContourPython Problem Overview
My simple Python code is this
import cv2
img=cv2.imread('Materials/shapes.png')
blur=cv2.GaussianBlur(img,(3,3),0)
gray=cv2.cvtColor(blur,cv2.COLOR_BGR2GRAY)
returns,thresh=cv2.threshold(gray,80,255,cv2.THRESH_BINARY)
ret,contours,hierachy=cv2.findContours(thresh,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)
for cnt in contours:
area=cv2.contourArea(cnt) #contour area
if (area>1220):
cv2.drawContours(img,[cnt],-1,(0,255,0),2)
cv2.imshow('RGB',img)
cv2.waitKey(1000)
print(len(cnt))
import numpy as np
contours=np.array(contours)
print(contours)
This worked fine. But recently without me even making any changes. This was throwed to me
> ret,contours,hierachy=cv2.findContours(thresh,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE) > > ValueError: not enough values to unpack (expected 3, got 2)
Python Solutions
Solution 1 - Python
the function cv2.findContours()
has been changed to return only the contours and the hierarchy and not ret
you should change it to:
contours,hierachy=cv2.findContours(thresh,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)
Solution 2 - Python
Well explained in this python code example, the best way to make your code version-proof is with this following syntax:
# check OpenCV version
major = cv2.__version__.split('.')[0]
if major == '3':
ret, contours, hierarchy = cv2.findContours(im.copy(), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
else:
contours, hierarchy = cv2.findContours(im.copy(), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
This provides you with a code that could run on either last or older version of OpenCV.