FAX is basically a technique of reproducing a document electronically at a distant place. FAX machine is an example of digital communication system.
Uses of a fax machine:
(a) It sends all the data over the telephone lines. Even the images are converted into digitized form and then are sent over the telephone lines.
(b) It also does the task of receiving the digitized image information. Then it reconstructs the image by doing the decoding of the digitized image.
Some steps are followed to send the data through fax. These are:
1. Some sensors are used at the receiving ends to read the received paper.
2. Black and white spots are marked on the paper at the sending end. This is done to make the travelling of the data possible over telephone line.
3. A mechanism is used to understand this coming data in the form of black and white dots, and to reproduce the original document by reading these dots at the receiving end.
Today Group3 facsimile machines are the most popular machines used by the majority. Those machines which belong to these groups are capable of communicating with similar machines of Group 3.
Let’s now discuss about these machines. These machines have a resolution of 8 pixels per inch. These machines use two distinct vertical resolutions. These can transmit data at a rate of 14400 bits per second. Sometimes the noise present over the line decreases the data rate up to some extent. These machines use a photodiode sensing array so that the complete line of the page can be scanned at a time. It consists of 1728 sensors. Paper illumination is also done to provide the clear view of the paper to the sensor.
To control the no of bits of the transmission different types of compression types are used:
(a) Modified Read
(b) Modified Huffman
The scanned document travels over the telephone line in the form of bits. At the receiving end decoding, decompressing and reassembling of the document lines is done. In this way we get the original document.