Glossary for Geospatial Science

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.