This is called interlacing. This is the American standard known as NTSC which stands for the National Television Standards Committee. Persistence of vision Remember the Fourth of July. Someone is waving a sparkler so fast it looks like there is a circle of light instead of just a ball of fire. The sparkler was moving faster than your eyes could adjust so the circle seemed to be there.
TV uses the same principle.
The three color dots move so fast across and down the screen, striking the phosphor coating on the back of the screen and creating the illusion of a large pi cture. The video signal is encoded magnetically.