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Symbols >15 9 >15 >15 >15 9 >15 >15 4 >15 Encoded stream 0 11001 0 0 0 11001 0 0 10100 11111 26 bits

Decoded stream 16w 9wb 16w 16w 16w 9wb 16w 16w 4wb 15w

FIGURE 12.8 Variable-to-variable run-length coding using Huffman coding assume a scanning resolution of 200 dots/inch in the horizontal direction and 100 dots/inch in the vertical direction. For an 8.5-x-11-inch standard North American document, the scanning process will produce 8.5 x 200 x 11 x 100 = 1,870,000 pixels. Because each pixel is represented by one bit, each page corresponds to 235 kilobytes where a byte consists of eight bits. Using a modem that transmits at a speed of 10,000 bits per second, we see that the transmission of each page will require about 3 minutes. Clearly lossless data compression is desirable in this application.

The ITU considered a set of eight documents, listed in Figure 12.9, in defining the facsimile coding standards. These documents are a business letter, a

Documents scanned at 200 x 100 pixels/square inch

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