The guy who invented the TV about 80 years ago scanned the light on a frame with a light capturing tube, and displayed what he captured on a picture tube. That was the first TV. the Image quality was horrible, but it was a wonder at that time.
This slowly evolved from monochrome to multi color TV sets, then the size of the picture tube expanded, and when the quality or the resolution went low, the screens became LCD, Plasma and recently LED.
These new breed of TVs have computers inside them that increases the low resolution images that they receive to fit the huge screen.
A newer breed of TVs, which are called HDTV have come around that are fit for playing Blu Ray discs that give you the absolute picture quality to feast your eyes. If your great grandfather who was proud of the TV that he bought 70 years ago, he would get a heart attack.