Pre vs Post processing

We live in a digital world.  One of the many advantages of digital data is that it can be easily manipulated.  

Preprocessing ultrasound echo data refers to any manipulation of the data BEFORE it is stored in memory.  

Postprocessing of the ultrasound echo data refers to any manipulation of the data AFTER it is stored in memory.

You cannot differentiate a preprocessing function from a postprocessing function on a live image.  Both pre and postprocessing can be applied to a live image.  The simple way to differentiate a preprocessing function from a postprocessing function is to FREEZE the image, then apply the function.  If the function does NOT work on a frozen image, it must be a preprocessing function.

Summary: Preprocessing can only be applied to a live image.  Postprocessing can be applied to a live AND a frozen image.