1. A video display system which builds an image
on the VDU in two phases, known as "fields", consisting of
even and odd horizontal lines.
The complete image (a "frame") is created by scanning an
electron beam horizontally across the screen, starting at the
top and moving down after each horizontal scan until the
bottom of the screen is reached, at which point the scan
starts again at the top. On an interlaced display, even
numbered scan lines are displayed in the first field and
then odd numbered lines in the second field.
For a given screen resolution, refresh rate (frames per
second) and phosphorpersistence, interlacing reduces
flicker because the top and bottom of the screen are redrawn
twice as often as if the scan simply proceded from top to
bottom in a single vertical sweep.