title: OpenCV Error: Assertion failed (scn == 3 || scn == 4) in cvtColor
body: <p>I'm new to OpenCV, I am getting Assertion failed error when I run a template matching code. The error message is given below</p>
  
  <pre><code>OpenCV Error: Assertion failed (scn == 3 || scn == 4) in cvtColor, 
  file /home/travis/miniconda/conda-bld/conda_1485299292920/work/opencv-
  3.2.0/modules/imgproc/src/color.cpp, line 9748
  Traceback (most recent call last):
  File "opencv_basics.py", line 6, in &lt;module&gt;
     img_gray = cv2.cvtColor(img_rgb, cv2.COLOR_BGR2GRAY)
  cv2.error: /home/travis/miniconda/conda-
  bld/conda_1485299292920/work/opencv-
  3.2.0/modules/imgproc/src/color.cpp:9748: error: (-215) scn == 3 || 
  scn == 4 in function cvtColor
  </code></pre>
  
  <p>This the code I'm trying to run. </p>
  
  <pre><code>import cv2
  import numpy as np
  
  #Template Matching
  img_rgb = cv2.imread('opencv-template-matching-python-tutorial.jpg')
  img_gray = cv2.cvtColor(img_rgb, cv2.COLOR_BGR2GRAY)
  
  template = cv2.imread('opencv-template-for-matching.jpg',0)
  w, h = template.shape[::-1]
  
  res = cv2.matchTemplate(img_gray,template,cv2.TM_CCOEFF_NORMED)
  threshold = 0.8
  loc = np.where( res &gt;= threshold)
  
  for pt in zip(*loc[::-1]):
      cv2.rectangle(img_rgb, pt, (pt[0] + w, pt[1] + h), (0,255,255), 2)
  
  cv2.imshow('Detected',img_rgb)
  </code></pre>
  
  <p>The gdrive folder link for the images used is <a href="https://drive.google.com/open?id=0B717wCPy7sE8SFdzNUp0U2l2U00" rel="nofollow noreferrer">here</a></p>
  
  <p>I tried reinstalling opencv3 but it is vain. 
  I'm using python 3.5 and OpenCV 3.2.0.</p>