title: How to properly index a NumPy array with stored images?
body: <p>I am trying to understand the output of <code>cv2.imread</code>.</p>
  
  <p>I have loaded PNG images into a NumPy array as grayscale. I think I have succeeded in doing so. I understand that <code>imagesList[0]</code> gives me a NumPy array of the first image, however I don't understand what the numbers within <code>imagesList[0][1]</code> correspond to. In that same vein of questioning, what would the numbers correspond to an <code>(m, n, 3)</code> image?</p>
  
  <pre><code># cv2 is openCV, an image processing package 
  import numpy as np
  import cv2
  
  #start and ending slice
  startSlice = 753
  endSlice = 823
  
  # each image array will be stored in the list.
  # imagesList[0] = first slice, imagesList[-1] = last slice
  imagesList = []
  
  # reading the image as a greyscale array, and storing into imagesList
  for i in range(startSlice,endSlice+1):
    fileName = "/somefilelocation"+'{0:04}'.format(i)+'.png'
    im = cv2.imread(fileName,0)
    imagesList.append(im)
    print(fileName)
  </code></pre>