Invisibility and Readability of Temporally and Spatially Intensity-Modulated Metaimage for Information Hiding on Digital Signage Display System

This paper describes a display technique that enables us to invisibly embed a metaimage into a color component of a displayed cover image by using a temporally, spatially, color-intensity-modulated metaimage and to extract it. We first examined invisibility in terms of color components for a temporally and spatially intensity-modulated metaimage in a displayed cover image. The results obtained from these experiments revealed that the invisibility with which the metaimage was embedded in the blue color component was much higher than that of the red and green components. Our experiments also revealed that the red and green components could not be used for a color component in which the metaimage was embedded. We also proposed and evaluated a new technique of improving the readability of an invisibly embedded metaimage in a displayed cover image captured with a video camera. The proposed technique uses two methods. A proposed method of calculating an estimated grayscale metaimage enabled us to obtain a value for the binarizing threshold from its histogram by using the correlation between color components in which the metaimage was either embedded or not embedded. A proposed method of calculating an estimated binary metaimage could drastically reduce noise caused by the cover image by using the obtained value of the binary threshold and size feature parameters of the embedded metaimage. The readability of the metaimage was drastically improved by using these methods.