Abstract
We have developed an invisible code for smart phones that consists of high-frequency blocks and low frequency blocks. Finder patterns composed of high-frequency and low-frequency blocks are placed around the corners of the code to enable the code to be embedded in several places. Two key technologies were devised to implement this idea. One is high-frequency blocks composed of bright and dark elements in a checkerboard pattern. The other is a method of reading the code that employs edge detection to extract the code from a photograph of an image in which the code is embedded. To verify the effectiveness of our invisible code, we estimated the reading accuracy for code embedded in four common types of images. The results demonstrate 100% of accuracy could be achieved at distance of 100-150 mm.
