interlacing

1. hardware 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 phosphor persistence, 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.

2. graphics progressive coding.

(1998-02-25)