Teletext is an analog TV system, the TV screen displays 25 frames of TV signals per second, each frame is 625 lines, each line is swept from the left to the right of the screen, and each frame is swept from the top to the bottom of the screen in two fields. Of the 625 lines per frame, only 575 lines are actually displayed on the screen, and the remaining 50 lines are backwards and cannot be seen. The reverse process is usually used to transmit additional data information, including graphics and text, in addition to transmitting test signals. At the receiving end, viewers can watch the transmitted information on the screen using a dedicated teletext decoder.
As a non-delivery newspaper, teletext has the reputation of "electronic newspaper". Teletext is easy to use, low in cost and easy to popularize, and all countries in the world are developing. Our country has already broadcast it in the program of CCTV, and some local TV stations have also broadcasted it one after another.
When watching TV programs at ordinary times, some words that appear on the TV screen are completely different from teletext broadcasts. These words are superimposed on the image signal by superimposing the characters described above and their similar devices on the image signal, and the transmission rate is very low; In text and television, characters and patterns are coded into digital signals, and certain lines during the TV blanking period are used to transmit this coded signal, and the transmission rate is much higher.
As a non-delivery newspaper, teletext has the reputation of "electronic newspaper". Teletext is easy to use, low in cost and easy to popularize, and all countries in the world are developing. Our country has already broadcast it in the program of CCTV, and some local TV stations have also broadcasted it one after another.
When watching TV programs at ordinary times, some words that appear on the TV screen are completely different from teletext broadcasts. These words are superimposed on the image signal by superimposing the characters described above and their similar devices on the image signal, and the transmission rate is very low; In text and television, characters and patterns are coded into digital signals, and certain lines during the TV blanking period are used to transmit this coded signal, and the transmission rate is much higher.
