====== qrcode ======
  * 二维码
  * [[http://www.iso.org/iso/home/store/catalogue_ics/catalogue_detail_ics.htm?csnumber=62021|ISO/IEC 18004:2015]]
  * [[https://github.com/zxing/zxing|zxing: java implementation ]]
  * [[https://github.com/fukuchi/libqrencode|libqrencode: a C library for encoding data in a QR Code symbol]]
  * [[https://www.nayuki.io/page/creating-a-qr-code-step-by-step|二维码生成详解，每一步都有示意图]]

===== 冗余纠错 =====
  * [[wp> Reed–Solomon_error_correction]]