ImageJ, calibrating an image to a physical scale using calibration?

[incalzirepardosealaq]

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.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.Is there a way to tell ImageJ, i.e. "the top left pixel is (-200mm,200mm) in physical space?