smission is simplex; there is no equipment structure, are used to transmit the page layouts for remote printing confirmation of reception. prior to local distribution. With printing deadlines paramount, high Analogue transmission is used and may be by PSTN, speech band scanning rates and wideband networks encouraged facsimile devel- private circuit, high frequency (h.f.) or long wave radio. There are opment and manufacturing teams to keep pressing at the then known several higher speed proprietary standards for equipment on broad- limits. cast distribution networks. Received image may be taken into an In the years before 1980 (when the CCITT G3 Recommendations editorial workstation for cropping, manipulation and onward pro- were published) there were really only specialist applications for cessing before printing. facsimile. Apart from those mentioned there were uses by govern- Moves towards a digital standard for compressed images pro- ment, military, police, for telegrams, colour transmissions received gresses slowly, relying on the CCITT/ISO JPEG work. Interwork- as separations and as colour prints, cloud photograph receptions ing may be possible at the application layer, but there seems no from weather satellites, etc. Many of these applications had differ- agreement on the communication layers at present. ent standards and formats, as demanded by the application, and was Indications are that compression around 1 bit/picture element acceptable since interworking was not necessary. (8:1) could be achieved for monochrome images. 60/4 Facsimile transmission contact during facsimile operation, normally transmitting in the Table 60.1 Comparison of facsimile terminal types: Continuous grey scale response. 2Analogue in scanning direction towards the mobile terminal. These units were costly for direction. 3 Continuous but limited grey scale. 4Includes their mobile environment and suffered as a result of needing spe- various grey scale and compression options cialised radio equipment. With the use of the TACS cellular