[纲要]交叉25码(itf)编码方法

[纲要]交叉25码(itf)编码方法 INTERLEAVED 2 OF 5 SYMBOLOGY (ITF) INTERLEAVED 2 OF 5 BACKGROUND INFORMATION Interleaved 2 of 5 is a higher-density numeric symbology based upon the Standard 2 of 5 symbology. It is used primarily in the distribution and warehouse industry. Interleaved 2 of 5 encodes any even number of numeric characters in the widths (either narrow or wide) of the bars and spaces of the barcode. Unlike Standard 2 of 5, which only encodes information in the width of the bars, Interleaved 2 of 5 encodes data in the width of both the bars and spaces. This allows Interleaved 2 of 5 to achieve a somewhat higher density. The symbology is called "interleaved" because the first numeric data is encoded in the first 5 bars while the second numeric data is encoded in the first 5 spaces that separate the first 5 bars. Thus the first 5 bars and spaces actually encode two characters. This is also why the barcode can only encode an even number of data elements. A typical Interleaved 2 of 5 barcode is: Note that the above barcode is physically smaller than its equivalent representation using Standard 2 of 5. NOTE: Interleaved 2 of 5 is essentially identical to Standard 2 of 5 except for the fact that Interleaved 2 of 5 encodes information in both the bars and spaces while Standard 2 of 5 only encodes information in the bars. However, the encoding scheme is the same for both in terms of their use of wide and narrow elements for each element. COMPUTING THE CHECKSUM DIGIT Interleaved 2 of 5 is similar to Standard 2 of 5 in the sense that it may include an optional modulo 10 check digit. Please see the section concerning Computing the Checksum digit in the Standard 2 of 5 page. The process for calculating the check digit is the same in Interleaved 2 of 5 as it is in Standard 2 of 5. And, like Standard 2 of 5, the checksum digit is optional. NOTE: In the case of Interleaved 2 of 5, the total length of the value to be encoded must be even. If you are going to compute and append a checksum value, the actual data itself must be odd in length such that when the additional checksum value is appended, the total length will be even. ENCODING THE SYMBOL In the following text, we will discuss the encoding of the barcode by considering that the number "1" represents a "dark" or "bar" section of the barcode whereas a "0" represents a "light" or "space" section of the barcode. Thus the numbers 1101 represents a double-wide bar (11), followed by a single-wide space (0), followed by a single-wide bar (1). This would be printed in the barcode as: STRUCTURE OF AN INTERLEAVED 2 OF 5 BARCODE An Interleaved 2 of 5 barcode has the following physical structure: 1. Start character, encoded as 1010. 2. Each pair of data characters is encoded (see encoding table below). 3. Stop character, encoded as 1101. INTERLEAVED 2 OF 5 ENCODING TABLE This table indicates how to encode each digit of an Interleaved 2 of 5 barcode. Note that the encoding is expressed as "N" (narrow bar or space) or "W" (wide bar or space). 0 NNWWN 1 WNNNW 2 NWNNW 3 WWNNN 4 NNWNW 5 WNWNN 6 NWWNN 7 NNNWW 8 WNNWN 9 NWNWN NOTE: The above encoding table is identical to that used with Standard 2 of 5. The only difference is that Interleaved 2 of 5 interleaves the encodings in the bars and spaces whereas Standard 2 of 5 only encodes data in the bar widths. ENCODING EXAMPLE We will now code the above example in Interleaved 2 of 5: "12345670". By this point we would already have calculated the checksum digit as "0" (the last digit of the barcode value) as illustrated in the checksum calculation section illustrated above. Now we need to encode each digit using the encoding table above: 1. The digit "1" encoded in bars: WNNNW 2. The digit "2" encoded in spaces: NWNNW 3. The digit "3" encoded in bars: WWNNN 4. The digit "4" encoded in spaces: NNWNW 5. The digit "5" encoded in bars: WNWNN 6. The digit "6" encoded in spaces: NWWNN 7. The digit "7" encoded in bars: NNNWW 8. The digit "0" encoded in spaces: NNWWN That is to say the digits 1 and 2 are encoded together, 3 and 4 are encoded together, 5 and 6 are encoded together, and 7 and 0 are encoded together. The first digit of each pair is encoded in the width of the bars and the second digit of each pair is encoded in the width of the spaces. For example, in the case of the first two digits "12", we encode the "1" in the bars using the sequence WNNNW (Wide bar, narrow bar, narrow bar, narrow bar, wide bar). We encode the "2" in the spaces that separate the bars of the first digit. The digit "2" is encoded in spaces with the sequence NWNNW (narrow space, wide space, narrow space, narrow space, wide space). Assuming "1" is a narrow bar, "11" is a wide bar, "0" is a narrow space, and "00" is a wide space, the above would be encoded as follows: BAR SPACE BAR SPACE BAR SPACE BAR SPACE BAR SPACE W N N W N N N N W W 11 0 1 00 1 0 1 0 11 00 Thus encoding the first two data digits results in the sequence 11010010101100. In other words, a wide bar, a narrow space, a narrow bar, a wide space, a narrow bar, a narrow space, a narrow bar, a narrow space, a wide bar, a wide space. The process for the rest of the pairs of characters is the same. It results in the following: 1. START CODE (always the same): 1010. 2. 1st and 2nd Digits: 11010010101100. 3. 3rd and 4th Digits: 11011010010100. 4. 5th and 6th Digits: 11010011001010. 5. 7th and 8th Digits: 10101001100110. 6. STOP CODE (always the same): 1101. This is shown in the following graphical representation where the barcode has been sectioned-off into areas that reflect each of the 6 components just mentioned.