類比電視
Analog television cameras scan an image as a series of horizontal lines that are stacked vertically to form a grid or "frame". The camera's progression through the frame is carefully controlled by electronic timers, known as time base generators, that produce smoothly increasing voltages. As the camera scans the image, the brightness of the location currently being scanned is also represented as a voltage. The series of varying voltages from the sensor forms an amplitude modulated (AM) signal that encodes the brightness variations along any given scan line. Additional voltage spikes are added to the signal to indicate when the line or frame ends.