Pagefax equipment

Weatherfax equipment

Photofax equipment

Facsimile types

Excluding the document facsimile equipment, all other types per­form specialist functions and are exclusively separate transmit and receive units, for transmission in one direction. Document facsimile types are almost exclusively transceivers.

Table 60.1 summarises the characteristics of the different types of facsimile equipment.

It is used for the transmission of full tone photographs of size normally less than A4. Often the received picture is printed on photographic paper. The important requirements are not image size but correct aspect ratio, which is preserved by using the same index of co-operation.

Some scanners are designed to transmit colour separations from 35mm colour negatives using sequential transmission. Photofax equipment may be used, one transmitter to one receiver for example for sending news photographs from field locations, or one transmit­ter broadcasting on a wirephoto distribution network to many re­ceivers. The transmission is simplex; there is no equipment confirmation of reception.

Analogue transmission is used and may be by PSTN, speech band private circuit, high frequency (h.f.) or long wave radio. There are several higher speed proprietary standards for equipment on broad­cast distribution networks. Received image may be taken into an editorial workstation for cropping, manipulation and onward pro­cessing before printing.

Moves towards a digital standard for compressed images pro­gresses slowly, relying on the CCITT/ISO JPEG work. Interwork­ing may be possible at the application layer, but there seems no agreement on the communication layers at present.

Indications are that compression around 1 bit/picture element (8:1) could be achieved for monochrome images.

These equipments are usually operated on private circuits or radio networks, on a simplex broadcast basis. The analogue transmission involved limits transmission speed and this method of operation is being superseded by point to multipoint computer data transfer. Providing the raw data to the local processor allows action replays of changing conditions, which are not easily appreciated from the printed meteorological charts. The existing network base continues in operation supplementing the data network.

In this area there are no standards, the equipment being tailored to suit individual newspaper requirements. Compression and trans­mission characteristics, reproduction ratio, and image processing are all selected to suit production requirements in the remote print­ing of the full newspaper pages.

The savings in transportation costs and time, by using this equip­ment, funds sophisticated high speed transmission developments, including the transmission of colour separation with sequential receptions on the same receive mechanism.

Дата добавления: 2015-03-31