title: Why does skimage.color.rgb2gray behave differently on different devices?
body: <p>I'm having some troubles with the <em>skimage.color.rgb2gray</em> method. I'm using it to turn an image (some simple black lines drawn on a white canvas with Paint) with a Python3 program, which is this:</p>
  
  <pre><code>import matplotlib.image as mpimg
  from skimage import color
  
  img = mpimg.imread('Image (1).png')
  gray = color.rgb2gray(img)
  </code></pre>
  
  <p>and I've found out that it returns different arrays on two different devices.</p>
  
  <p>The first one is a Raspberry Pi 3 Model B (OS: Raspbian GNU/Linux 8 (jessie)), and it returns this,</p>
  
  <pre><code>[[0.99999994 0.99999994 0.99999994 ... 0.99999994 0.99999994 0.99999994]
  [0.99999994 0.99999994 0.99999994 ... 0.99999994 0.99999994 0.99999994] 
  [0.99999994 0.99999994 0.99999994 ... 0.99999994 0.99999994 0.99999994]
  ...
  [0.99999994 0.99999994 0.99999994 ... 0.99999994 0.99999994 0.99999994]
  [0.99999994 0.99999994 0.99999994 ... 0.99999994 0.99999994 0.99999994]
  [0.99999994 0.99999994 0.99999994 ... 0.99999994 0.99999994 0.99999994]]
  </code></pre>
  
  <p>which is wrong, since the numbers should be 1.0, that's white.</p>
  
  <p>The second one is a Windows 10 Home (1803 version), where everything runs smoothly:</p>
  
  <pre><code>[[1. 1. 1. ... 1. 1. 1.]
  [1. 1. 1. ... 1. 1. 1.]
  [1. 1. 1. ... 1. 1. 1.]
  ...
  [1. 1. 1. ... 1. 1. 1.]
  [1. 1. 1. ... 1. 1. 1.]
  [1. 1. 1. ... 1. 1. 1.]]
  </code></pre>
  
  <p>Could someone explain me the reason for this? Thanks in advance!
  If some other details are needed, tell me.</p>