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Interlaced signals are broken up into alternating fields. The upper and lower fields each shows half of the total video frame. Each field is shown for half of the time a frame is shown. So 1 frame of interlaced video has two different fields that display the upper and then lower fields. Progressive signals are full frame images, so when you see one frame of a progressive signal, it’s the entire image in a single frame.

The interlaced signal was invented by Leon Theremin, who also invented the musical instrument that shares his last name in the 1927. Interlaced was the only standard in town for television until 1993, then the FCC tested the first broadcast progressive system. Progressive monitors had been around for a few decades thanks to computer monitors before being adopted into the television world.

Here’s an animated graphic to assist in understanding how interlaced systems display images:

Here are some more resources for learning about interlaced vs progressive:

• The Big Picture – Interlaced vs. Progressive, Fields vs. Frames – http://www.animemusicvideos.org/guides/avtech/video2.htm
• Interlaced vs Progressive Signals – http://hubpages.com/hub/interlaced-vs-progressive
• Wikipedia: Interlace – http://en.wikipedia.org/wiki/Interlace