title: Correct crop of CIGaussianBlur
body: <p>As I noticed when CIGaussianBlur is applied to image, image's corners gets blurred so that it looks like being smaller than original. So I figured out that I need to crop it correctly to avoid having transparent edges of image. But how to calculate how much I need to crop in dependence of blur amount?</p>
  
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  <p>Example:</p>
  
  <p>Original image:<br>
  <img src="https://i.stack.imgur.com/fnwru.png" alt="enter image description here"></p>
  
  <p>Image with 50 inputRadius of CIGaussianBlur (blue color is background of everything):<br>
  <img src="https://i.stack.imgur.com/wqHRF.png" alt="enter image description here"></p>