The eye can move from spot to spot to examine details, but in essence, the entire picture is seen at one time. Likewise, when watching a film, the eye sees moving images go by on the screen. The illusion of motion is created by projecting many pictures or frames of film each second. The eye perceives motion, even though the film is made up of thousands of individual still pictures. Video is different from film in that a complete frame of video is broken up into component parts when it is created.
In a tube camera, the electron beam transforms a light image into an electronic signal. Then, an electron beam within a CRT video receiver or monitor causes chemicals called phosphors to glow so they transform the electrical signal back into light.
The specifications for this process were standardized by the National Television System Committee, or NTSC, when the television system was originally conceived in the late 1930s. The NTSC standard was used in North America and parts of Asia and Latin America. As other countries developed their own television systems, other video standards were created. Eastern and Western Europe used a system called PAL (Phase Alternate Line). France and the countries of the former Soviet Union used a system known as SECAM (Séquential Colour Avec Mémoire, or Sequential Color with Memory). Most developed countries have switched to transmission of television using digital standards, making these analog formats obsolete. However, there are still places in the world where analog broadcasts remain.
NOTE: The United States switched to digital broadcasting in 2009, but the NTSC standard lives on in many consumer video products. Cable boxes, TV receivers, disk players and games often include an output simply labeled "video.