High-speed thermal printing and document feed technique for facsimile using MMR coding scheme over telephone network

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Modified MR (MMR) coding is the coding method for G4 facsimile. It has a better compression performance than the MR (modified read) code, which is a coding scheme for G3 facsimile. Consequently, the facsimile using the MMR code is expected to realize a high-speed transmission. In the facsimile using MMR code, a high-speed printing is also required to achieve such a highspeed transmission. From such a viewpoint this paper discusses the high-speed thermal printing, suited to the facsimile over the telephone network using the MMR code. A high-speed transmission by the black ratio control is considered, where the printing speed is varied according to the number of black pixels in the line. Detailed parameters are presented for the black ratio control which can realize almost the same printing speed as the transmission speed. Next, as the means toward a practical system, a high-speed document feed technique is considered, together with its realization, where the document feed is performed smoothly following the change of the printing speed. It is shown by computer simulation that the loss of the printing time due to this mechanism is at most 10 percent for the usual document. Finally, to reduce the number of feed stops in a page, a high-speed document feed is proposed where the maximum feed speed is limited according to the number of buffered coded bits. It is verified by computer simulation that a high-speed and smooth document feed can be realized without a stop for the usual document.