Novel techniques are described for hand-printed numeral recognition and generation of various-sized high-quality graphic characters, which permit efficient communications between facsimile terminals and computer centers. To achieve extremely precise numeral recognition despite the poor characteristics of the images obtained by facsimile terminals, a supplementary preprocessing method and a similar-shaped-character distribution method have been developed. Using these procedures, about 80% of the characters which cannot be recognized by the basic recognition procedure are rendered recognizable. Transmission bit errors affect encoded facsimile signals of an entry sheet in the form of recognition degradation or failure of row detection mark length. The occurrence probability of these kinds of errors is estimated, and it is shown from the degree of recognition degradation that the impact is negligibly small from the standpoint of practical use. A novel smoothing method for code-to-pattern conversion has also been developed to improve the picture quality of graphic character patterns.>

An interframe coding system is described which is capable of transmitting both 4-MHz videotelephone signals and NTSC color TV signals at an average rate of 6.312 Mbits/s. The coding system takes as much advantage as possible of in-frame correlation, in addition to interframe correlation, by coding pel-to-pel difference of interframe difference (combinational difference). Variable-length word coding is effectively used to reduce the number of bits to be transmitted. In order to prevent buffer overflow, luminance and spatial resolutions are controlled. To control luminance resolution, interframe difference is multiplied by a coefficient\alpha \leq 1, so that value approaches zero when violent motion causes the buffer to fill. Though multiplication with small α results in temporal resolution reduction in moving areas, quality degradation is not too marked. Spatial resolution control is achieved by using subsample and subline coding modes.

As a powerful tool for economizing on the digital transmission of videotelephone signals, interframe coding techniques have drawn increasing attention, and various interframe coding schemes have been proposed recently. However, many problems remain to be studied in establishing technical feasibility for these techniques and schemes. This concise paper reports on field trial in which a 1.544-Mbits/s digital transmission of videotelephone signals was conducted over Nippon Telegraph and Telephone Public Corporation's (NTT's) PCM100M digital repeatered line between Tokyo and Yokohama, Japan. The experimental interframe codec is based on the well-understood conditional picture element replenishment algorithm. The object of the field trial was to demonstrate, not the validity of the algorithm itself, but the technical feasibility of the interframe coding system as an entity. Experimental results are satisfactory enough to assure us of the system's practicality in the near future.