title: scikit-image: write a ndarray to image with imsave, read back with imread, data don't match
body: <p>here is the minimum working example:</p>
  
  <pre><code>import numpy as np
  from skimage.io import imsave, imread
  
  image = np.array([[[109, 232, 173],
                  [ 55,  35, 144]],
                  [[ 43, 124, 185],
                  [234, 127, 246]]], dtype=np.uint8)
  
  imsave("test.jpg", image)
  rb_image = imread("test.jpg")
  print("original image")
  print(image)
  print("read back image")
  print(rb_image)
  </code></pre>
  
  <p>after run it, the result is, the ndarray read back from file don't match with </p>
  
  <pre><code>original image
  [[[109 232 173]
    [ 55  35 144]]
  
   [[ 43 124 185]
    [234 127 246]]]
  read back image
  [[[111 208 255]
    [ 42  61 138]]
  
   [[ 72 140 201]
    [141 131 218]]]
  </code></pre>
  
  <p>can some one give me some suggestiones? </p>