title: ImageJ, calibrating an image to a physical scale using calibration?
body: <p>I want to be able to calibrate an image to a physical distance, so that I can crop the image to a physical distance rather than giving the pixel number to crop to.
  I have seen the Calibration class in the ImageJ API and I can set the calibration to set the pixel dimensions and to state where the origin of my image is by setting Xorigin and Yorigin variables.</p>
  
  <p>What if my image does not contain the origin or what if one pixel does describe the origin i.e. two pixels may run from -0.3cm to 0 and 0 to +0.3cm.</p>
  
  <p>Is there a way to tell ImageJ, i.e. "the top left pixel is (-200mm,200mm) in physical space?</p>