Abstract
We have previously proposed the artificial fiber (AF) patterns in order to be able to hide information in printed documents. AF pattern uses the features of the medium (e.g., paper). It has some special characteristics of low visibility of the hidden information, print-scan robustness, device independent property and geometrical/rotational invariance. On the other hand it also has a weakness regarding foreground robustness and extraction threshold instability when using a camera as an input device. In the past several challenges we have proved foreground robustness only in case of adding AF pattern on foreground objects. It has been difficult to extract information in case of adding a foreground object on AF pattern by a distortion of its low frequency part. Also we found extraction threshold instability was caused by an uneven illuminance when using a camera. In this paper we proposed using the calculated intensity ratio of adjacent AF patterns for improving an uneven illuminance at camera usage then covering foreground objects with the AF pattern by detecting a contour of foreground objects for improving foreground robustness. We proved these proposals are very effective for improving weaknesses of the AF pattern by several experiments.
