title: Relationship of standard deviation for Gaussian filter between pixel domain and the real world
body: <p>I constructed an experiment with Gaussian blur in real world and MR images. I printed some test images blurred and compare augmented images blurred too.</p>
  
  <p>What is the best way to express how much blurring I applied in real-world coordinates?</p>
  
  <p>The image is 2560x1440 pixels, corresponding to 533x300 cm in the real world. If this image is blurred with a Gaussian with standard deviation <code>n</code> (filter size is <code>ceil(3 * n) * 2 + 1</code>), how can this be expressed in centimeters? Is it reasonable to express it as the real size of the filter in centimeters?</p>