Invisible and Readable Checkerboard as Watermark With Temporally Brightness Modulation

Abstract

This aticle describes invisibility and readability in terms of the size of the basic unit of information that was attached to a displayed image by using our proposed method. The proposed method enables us to invisibly attach information to a displayed image on a flat panel display (FPD) and to extract the information from a captured video image of the displayed image. The information was attached to a single-color component of the displayed image by using temporal and spatial brightness modulation. The information was arranged within a given rectangular area of the displayed image as a black-and-white checkerboard pattern. The checkerboard pattern was used because it is a typical example of a t2-D pattern with a high density. The checkerboard pattern consists of squares having the same side length <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> . <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> was changed to examine the invisibility and readability in terms of the size of the basic unit of information. First, we assessed invisibility to the human eye of the information attached to the displayed image on the FPD. The experimental results showed that the degree of invisibility was 90% or over for all <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> when a frame rate for the displayed image was 60 fps. That is, the invisibility is independent of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> . We also examined readability of the attached information for a video camera. The experimental results showed a lower limit value of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> that satisfied the readability.