Optical Print Centering

The following script calculates the optically-centered print position and illustrates it graphically.

The units are arbitrary.  Fractions are optional.

Include the space between the mat and print edges if appropriate.  The preferred method is to center the mat window, but you may choose to center the print itself.

Rabbet width refers to the inner edge of the frame that overlaps the edge of the mount.  In the illustration, the frame stock is 3x the width of the rabbet.

Sometimes optical centering results in the top margin being narrower than the sides.  In that case, you will probably want to use one of the other centering options.