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주제: QR code specification

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  • QR code (Quick Response Code) - trademark for a type of matrix barcode (or two-dimensional barcode) first designed for the automotive industry in Japan.

  • A QR code uses four standardized encoding modes (numeric, alphanumeric, byte / binary, and kanji) to efficiently store data; extensions may also be used.

  • The QR Code system has become popular ue to its fast readability and greater storage capacity compared to standard UPC barcodes.

  • A QR code is processed using Reed–Solomon error correction until the image can be appropriately interpreted. The required data is then extracted from patterns present in both horizontal and vertical components of the image.

History                                                                    

The QR code system was invented in 1994 by Denso Wave. Its purpose was to track vehicles during manufacture; it was designed to allow high-speed component scanning. Although initially used for tracking parts in vehicle manufacturing, QR codes now are used in a much broader context, including both commercial tracking applications and convenience-oriented applications aimed at mobile-phone users (termed mobile tagging). QR codes may be used to display text to the user, to add a vCard contact to the user's device, to open a Uniform Resource Identifier (URI), or to compose an e-mail or text message. Users can generate and print their own QR codes for others to scan and use by visiting one of several paid and free QR code generating sites or apps. The technology has since become one of the most-used types of two-dimensional barcode

Error correction                                                                    
Codewords are 8 bits long and use the Reed–Solomon error correction algorithm with four error correction levels. The higher the error correction level, the less storage capacity. The following table lists the approximate error correction capability at each of the four levels:

Level L (Low) 7% of codewords can be restored.
Level M (Medium) 15% of codewords can be restored.
Level Q (Quartile) 25% of codewords can be restored.
Level H (High) 30% of codewords can be restored.

In larger QR symbols, the message is broken up into several Reed–Solomon code blocks. The block size is chosen so that at most 15 errors can be corrected in each block; this limits the complexity of the decoding algorithm. The code blocks are then interleaved together, making it less likely that localized damage to a QR symbol will overwhelm the capacity of any single block.

Thanks to error correction, it is possible to create artistic QR codes that still scan correctly, but contain intentional errors to make them more readable or attractive to the human eye, as well as to incorporate colors, logos, and other features into the QR code block

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