Adaptive predictive coding for newspaper facsimile

An adaptive predictive coding method, which efficiently encodes newspaper pages with printed text and screened photographs is presented. This coding technique utilizes two kinds of predictors with different reference picture elements (pels). One is applied to printed text and the other is applied to screened photographs. The Dth previous pel and its neighboring pels age adopted as the reference pels for the photograph predictor, where distance D coincides with the screen period. Comparing the adaptive predictive coding with a typical document facsimile coding, the data compression ratio is improved by about two times for a screened photograph (compression ratio is 5 ∼ 6) and is almost the same or slightly higher for printed text. Computer simulation shows that if a 500-kbits buffer memory is employed, it is possible to transmit most pages, including an extreme case of a 100 percent photograph page, with a 4500-rev/min scanner at a transmission bit rate of 128 kbit/s. For average pages the revolution speed can be raised to 6000 rev/min. Page transmission time of about 5 min in analog facsimile through a 48-kHz band can be reduced to 1.8 min by adopting the digital transmission with a 128-kbit/s data modem and the adaptive predictive coding technique, when the facsimile revolution speed is set at 6000 rev/min.