Illuminance-robust semipermanent 2D porous code

摘要

A semipermanent two-dimensional (2D) porous code has been developed that can be embedded in concrete with ultrasmall holes and read with smartphones. The code is made by high-frequency cells “1” composed of five shadows created by ultrasmall holes and low-frequency cells “0” without shadows. We can instantly embed the code in cement using a 3D-printed stamp with five needles in each high-frequency cell. To read the code, first, the code is processed as follows: conversion to grayscale, detection of edges with a differential filter, binarization, morphological dilation and erosion, and smoothing of brightness. Then, since the conventional 2D code is obtained, it is just decoded using the conventional 2D code reader. When the code is used as a QR code whose module size is 21×21 cells, the stamp for embedding the code, whose dimensions are 126 mm×126 mm, has needles formed with quadrangular pyramids that are 5 mm in height and their bases are 2 mm in side length. In an experiment using the stamp, we succeeded in reading the code under the illuminance of 10-6,500 lux and verified that our code is robust to illumination changes.