how ntsc video works

The NTSC system specifies 525 individual horizontal scan lines for each image. Here's how it works:

1. The scanning beam scanning every other horizontal line, from the top of the image to the bottom, which equals one field.

2. The beam completes one line at 15,734.27 Hz. That's 15,734.27 cycles per second! This is the horizontal scan rate.

3. The beam shuts off at the end of the first field.

4. Back at the top, the beam fills in the other half of the lines- the even numbered lines.

5. Two fields are scanned for every frame.

6. The two fields are displayed in immediate succession, creating the appearance of a single 525-line frame.

7. The beam scans all the lines in a frame at 59.94 Hz. This is a vertical scan rate of almost 60 cycles per second. This rate was chosen because it is compatible with the alternating current (AC) electricity supply of 60 cycles per second found in those regions where NTSC is used.

8. Color, for NTSC video, is carried at 3.58 MHz.

9. Sound, for NTSC video, is carried at 4.5 MHz.