Glossary for Geospatial Science

  Technical vocabulary defined by MicroImages

book Glossary

interlaced video:   Background: The image you see on a TV screen is made from a set of about 480 horizontal lines.  The lines are projected in two passes of the signal beam.  Each pass only projects every other line of the image: the odd lines in one pass, and the even lines in the next pass.  One scan takes 1/60 of a second, so the whole picture (the frame) is refreshed every 1/30th of a second.  There is a time difference of 1/60 of a second between any pair of adjacent lines in a frame.

Thus, a single, still video image of 1/30 of a second duration consists of two interlaced fields of the source video signal.  Displaying a single frame of interlaced video causes vertical jitter.  This jitter is especially pronounced when an image contains horizontal lines.  This is called umpire shirt jitter on conventional broadcast TV and can be seen along the black and white edges of an umpire’s shirt or along the sharp horizontal edges of large letters.  This effect can cause eye strain.  Interlace jitter is best overcome by using a monitor with long-persistence phosphor.  This phosphor holds each line longer until it can be refreshed by the next scan.