The problems should be thought when the principle of
subtraction acts. Subtraction is suit to use in some special
circumstances where the signal object can change with time or
frame. The more memory is needed to store the data of
background image using subtraction principle than other
CCD Camera Light pen
Computer Workpiece
LEDs methods. It is necessary to keep the CCD camera and
background invariable at the time of measurement so that the
efficient data of image can be obtained subtracting the
background from the image with lighted LEDs. Fortunately,
the result is good though light pen is shaken a little inevitably
in measuring process.