title: PIL Image Convert from RGB to YCbCr Results in 4 Channels Instead of 3 and Behaves Like RGB
body: <p>Well, the title is pretty self explanatory. I have an image file that I want to separate into Y, Cb and Cr respectively. After opening the file, convert it from RGB (which is the default mode when opening an image file) into YCbCr and then turn it into an array using numpy.array(), it resulted in a 2D array with 4 channels, which is not I expected as according to the documentation in <a href="http://www.nmt.edu/tcc/help/pubs/pil/pil.pdf" rel="noreferrer">http://www.nmt.edu/tcc/help/pubs/pil/pil.pdf</a></p>
  
  <p>Here is what I do in the interpreter:</p>
  
  <pre><code>ImageFile = Image.open('filePath', 'r')
  ImageFile = ImageFile.convert('YCbCr')
  ImageFileYCbCr = numpy.array(ImageFile)
  ImageFileYCbCr
  </code></pre>
  
  <p>resulted in</p>
  
  <pre><code>array([[[103, 140, 133,  95],
      [140, 133,  91, 141],
      [132,  88, 141, 131],
      ..., 
      [129,  65, 146, 129],
      [ 64, 146, 130,  65],
      [146, 129,  64, 147]],
  
     [[129,  64, 147, 129],
      [ 62, 149, 130,  62],
      [149, 130,  62, 149],
      ..., 
  </code></pre>
  
  <p>And when I separate it into its channels</p>
  
  <pre><code>ImageFileY = copy.deepcopy(ImageFileYCbCr) # to make a separate copy as array is immutable
  ImageFileY[:,:,1] *= 0
  ImageFileY[:,:,2] *= 0
  ImageFileY[:,:,3] *= 0
  ImageFileYOnly = Image.fromarray(ImageFileY)
  ImageFileYOnly.show()
  </code></pre>
  
  <p>It resulted in a red color channel as if it is an RGB. Ho can I get the Y, Cb, Cr values respectively?</p>
  
  <p>EDIT: Numpy version 1.3, Python 2.6 Linux Backtrack 5</p>