How does the fax machine transmit information?

The emitted light and the condenser lens converge into a light spot, and then irradiate the image attached to the transmission drum. The drum moves horizontally and rotates relative to the light spot. In this way, the light spot scans the image line by line and decomposes the image into many pixels with the same size as the light spot. Each pixel has different shades of black and white, so it reflects light with different brightness after being irradiated by a light spot. With the change of light and shadow, the light beam is received by the objective lens and then irradiated to the photoelectric converter, which is converted into a photovoltaic cell.

Then these signals are modulated and amplified and sent to various wired and wireless communication circuits for uploading and outputting. This problem is not difficult to understand. We just need to understand its principle. The fax machine decomposes the manuscript into many tiny units in a specified order through an optical scanning system, which are actually called pixels. Then, the brightness information of these tiny units is converted into electrical signals by photoelectric converters in turn, which are amplified, encoded or modulated and then sent to the channel.

After amplifying, decoding or demodulating the received signal, the receiver copies the original copy in the form of recording at the same scanning speed and order as the transmitter. Moreover, fax machine is a kind of communication equipment that uses scanning and photoelectric conversion technology to convert static images such as documents, charts and photos into electrical signals, and then transmits them to the receiving end for copying in the form of records.

Usually, fax is the most convenient way to send the signature and seal of the other party in real time, or print the document confirming the certificate and then send it back. In addition, many fax machines are integrated with printers, so as long as you set up automatic reception when the other party forges something, you don't have to send a signal to receive something as before, and print it directly, so many people find it very convenient, and there is no backward information transmission mode mentioned in the original post.

The question of how the fax machine transmits information is explained here today.