The NTSC Signal: The Good, The Bad, The Ugly

In 1953, the National Television Systems Committee (NTSC) devised an American standard for the video signal that's still used today. Understanding this standard offers insight as to how your camcorder records and delivers a video signal. The NTSC standard has served us rather well during a century filled with the most rapid technological changes in human history, but with the arrival of HDTV, is it in its last days?

Look at that Screen
If you look closely at your television picture, you'll see that it's not a continuous image but rather a series of horizontal lines. Phosphors--compounds that emit light when they are hit with an electron beam--coat the face of your picture tube. An electron beam traces lines across the picture tube (525 of them every 30th of a second), lighting up the phosphors and generating a picture. The moving pictures that you record with your camcorder are actually a series of still images. When these stills run at a fast enough speed, your eye perceives them as one continuous moving image. But even 30 frames per second is not fast enough. The resulting picture still appears to have a little flicker.

Engineers solved this problem by dividing each frame into two fields--one containing the odd number of lines and the other containing the even number of lines. The electron beam traces out the odd numbered lines, then goes back to the top and puts the even lines in between. This process is called interlaced scanning. Now the system displays 60 fields per second, and the viewer can no longer see the…