Embedding overlay information in images on four color displays

Abstract

A method to embed overlay information such as captions and annotations in images is proposed. The overlay information is mixed and hidden in one of the color components on a display having redundant color representation capabilities. Normal viewers do not see the hidden information since other color components are adjusted such that a resulting image has the same combination of primary colors as the original one. The hidden information could be extracted by simple filtering and would be overlaid in images on proprietary viewer screens. In this paper we assume that the display has yellow pixels in addition to the normal RGB colors which we exclusively use to transmit the overlay information. We derive a formula for the color components to keep the overlay image invisible taking into account the nonlinearity of the display characteristics. The dynamic range of the overlay channel is limited by the image contents. We compute the channel capacity for some test images. We have conducted fundamental experiments where the monitor has been emulated by a normal three color display and have verified that the hidden information can be made almost invisible if nonlinearity of the display is properly compensated.