title: How to extract green channel from RGB image in Python using Scikit-Image library?
body: <p>I am extremely new to scikit-image (<code>skimage</code>) library in Python for image processing (started few minutes ago!). I have used <code>imread</code> to read an image file in a <code>numpy.ndarray</code>. The array is 3 dimensional where the size of the third dimension is 3 (namely one for each of Red, Green and Blue components of an image). </p>
  
  <pre><code>rgb_image = imread("input_rgb_image.jpg")
  rgb_image.shape # gives (1411L, 1411L, 3L)
  </code></pre>
  
  <p>I tried to extract green channel as:</p>
  
  <pre><code>green_image = rgb_image[:,:,1]
  </code></pre>
  
  <p>But when I write this image matrix to an output file as:</p>
  
  <pre><code>imsave("green_output_image.jpg",green_image)
  </code></pre>
  
  <p>I get an image which doesn't really look ONLY green!</p>