title: Converting raw images to tiff by using rawpy module in python
body: <p>I'm new to image processing. I just wanted to get a tiff image from raw format(NEF). I used rawpy module to get the desired output, yet the tiff image is RGB with 4 channels. I couldn't know why there is a fourth channel in the new image? </p>
  
  <p>Can anyone please explain to me what is going on, and how I can get tiff image with three RGB channels?</p>
  
  <pre><code>import rawpy
  import matplotlib.pylab as plt
  
  
  raw_image = "DSC_0001.NEF"
  
  raw = rawpy.imread(raw_image)
  rgb = raw.postprocess()
  plt.imsave("new.tiff", rgb )
  
  image = plt.imread("new.tiff")
  
  print(image.shape)
  </code></pre>
  
  <p>The array shape is : (2868, 4310, 4) !  </p>