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A special end pattern that has bars on both ends is required to end the code. Two-width vs. many-width. A two-width, also called a binary bar code, contains bars and spaces of two widths, "wide" and "narrow". The precise width of the wide bars and spaces is not critical; typically, it is permitted to be anywhere between 2 and 3 times the width ...
A Data Matrix on a Mini PCI card, encoding the serial number 15C06E115AZC72983004. The most popular application for Data Matrix is marking small items, due to the code's ability to encode fifty characters in a symbol that is readable at 2 or 3 mm 2 (0.003 or 0.005 sq in) and the fact that the code can be read with only a 20% contrast ratio. [1]
The codewords are represented by patterns of dark (bar) and light (space) regions. Each of these patterns contains four bars and four spaces (where the 4 in the name comes from). The total width is 17 times the width of the narrowest allowed vertical bar (the X dimension); this is where the 17 in the name comes from.
Rendition of SD ECR-1-1978 color bars Colors are only approximate due to different transfers and color spaces used on web pages and video (BT.601 or BT.709). SMPTE color bars are a television test pattern used where the NTSC video standard is utilized, including countries in North America.
All widths are multiples of a basic "module". Each bar and space is 1 to 4 modules wide, and the symbols are fixed width: the sum of the widths of the three black bars and three white bars is 11 modules. The stop pattern is composed of two overlapped symbols and has four bars. The stop pattern permits bidirectional scanning.
On the other hand, if a too small dot of light is used, then it can misinterpret any spot on the bar code making the final output wrong. The most commonly used dimension is 13 mil (0.013 in or 0.33 mm), although some scanners can read codes with dimensions as small as 3 mil (0.003 in or 0.075 mm). Smaller bar codes must be printed at high ...
The symbol is built on a square grid with a bull's-eye pattern at its centre for locating the code. Data is encoded in concentric square rings around the bull's-eye pattern. The central bull's-eye is 9×9 or 13×13 pixels , and one row of pixels around that encodes basic coding parameters, producing a "core" of 11×11 or 15×15 squares.
Code 39 was developed by Dr. David Allais and Ray Stevens of Intermec in 1974. Their original design included two wide bars and one wide space in each character, resulting in 40 possible characters. Setting aside one of these characters as a start and stop pattern left 39 characters, which was the origin of the name Code 39. [2]