In the TV receiver, there is a wonderful "painter"-the image agency. It uses an "electron gun" as a brush and a fluorescent screen as a drawing board, and all the strokes drawn are controlled by the developer's "photographer". When the received electric signal is large, the electron gun emits more "bullets"-electron rays, and the screen emits bright spots; On the contrary, it will show black spots. Although these bright and dark spots are discontinuous, the human eye has the characteristic of "visual persistence" (when observing an object for a long time, it is about 1/30 ~ 1/5 seconds in a short time after the eyes leave the object or move away from the eyes, and the average is about110 seconds. This slowly disappearing phenomenon is called "visual persistence"), so we look exactly like the real image. There are many adjustment knobs on the TV receiver, such as "volume knob", "brightness knob" and "black and white contrast knob", which can be adjusted as usual when watching radio and television.