title: explain ground-thruth .mat file of an image for CNN
body: <p>good evening,</p>
  
  <p>i'm new to coding CNN
  i'v got ShanghaiTech crowd counting dataset that has (beside the images) .mat files for what i believe the ground truth for (counting) for images.</p>
  
  <p>i try to print the content of one .mat file in python, here is what i get:</p>
  
  <pre><code>{'image_info': array([[array([[(array([[ 855.32345978,  590.49587357],
     [ 965.5908524 ,  472.79472415],
     [ 937.09478464,  400.93507502],
     ...,
     [  42.5852337 ,  359.87860699],
     [1017.48233659,    8.99748811],
     [1017.48233659,   23.31916643]]), array([[920]], dtype=uint16))]],
    dtype=[('location', 'O'), ('number', 'O')])]], dtype=object), '__version__': '1.0', '__header__': 'MATLAB 5.0 MAT-file, Platform: PCWIN64, Created on: Fri Nov 18 20:06:05 2016', '__globals__': []}
  </code></pre>
  
  <p>each .mat file corresponds to one image,
  i know at some point in CNN we need to calculate the error between the network result and the ground truth we have, but i don't seem to understand the structure and the content of these .mat files.</p>
  
  <p>can someone explain whats in these files and how or for what that content is used in crowd estimation.</p>