Modem-HOWTO: Appendix G: Fax pixels (dots)

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## 27. Appendix G: Fax pixels (dots)

Here's some info on the bloated bandwidth required for standard fax including the dot density. You can of course send a fax via your modem if you dial the real telephone number of the recipient.

> `

>     A4 paper:    216mm (horizontal) * 297mm (vertical)
>     normal mode       8dots/mm      * 3.85dots/mm
>     fine   mode                     * 7.7dots/mm
>     extra fine mode                 *15.4dots/mm

> `

Each dot is either white or black and thus 1 bit. One sheet of A4 paper using fine mode is (216*8) * (297*7.7) = about 4 million dots. With a compression ratio of 8:1 it takes about 50 seconds at 9600bps for transmission.

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