The recognizable image or pattern that appears lighter or darker than surrounding paper when viewed with a light from behind the paper.

The meaning of the Greek word "gyro" in Gyricon e-paper is 

The genuineness of bank notes can easily be checked using the appropriate illumination to show the -------- in the paper and ink.

In this method, multicolored image on the blanket cylinder segment is first transferred onto a printing plate and then transferred onto a second blanket cylinder.

.STL file format in 3D printing refers to 

OPC Means