title: Python addition to array subset
body: <p>I have an image, which is an array: </p>
  
  <pre><code>self.imgData[0]
  </code></pre>
  
  <p>I do some operations already such as:</p>
  
  <pre><code>self.imgData[0] = self.imgData[0] * scalar
  </code></pre>
  
  <p>which will multiply every pixel in the image by scalar</p>
  
  <pre><code>self.imgData[0][self.imgData[0] &lt; -32767] = -32767
  </code></pre>
  
  <p>for any pixel less than -32767 set to -32767</p>
  
  <p>these both work fine, but when I try to use addition or subtraction:</p>
  
  <pre><code>self.imgData[0][self.imgData[0] &gt; 0] += 100.0
  </code></pre>
  
  <p>nothing is happening. and I do not know why, can any one help?</p>