title: Converting image from RGB to LUV and back results in different image
body: <p>I'm currently trying to start with an original RGB image, convert it to LUV, perform some operations (namely, rotate the hues), then rotate it back to RGB for display purposes. However, I'm encountering a vexing issue where the RGB-to-LUV conversion (and vice versa) seems to be changing the image. Specifically, if I begin with an LUV image, convert it to RGB, and then change it back to LUV, without changing anything else, the original image is different. This has happened for both the Python (cv2) and Matlab (open source) implementations of the color conversion algorithms, as well as my own hand-coded ones based on. Here is an example:</p>
  
  <pre><code>luv1 = np.array([[[100,6.12,0]]]).astype('float32')
  rgb1 = cv2.cvtColor(luv1,cv2.COLOR_Luv2RGB)
  luv2 = cv2.cvtColor(rgb1,cv2.COLOR_RGB2Luv)
  print(luv2)
  [[[99.36293    1.3064307 -1.0494182]]]
  </code></pre>
  
  <p>As you can see, the LUV coordinates have changed from the input. Is this because certain LUV coordinates have no direct match in RGB space?</p>