Invisibility

This chapter discusses the different strategies to ensure the invisibility of a message embedded in a color image. It focuses on the watermarking of color images that involves the framework of modern watermarking algorithms. A more detailed understanding of the processing of color by the human visual system would improve the invisibility of a mark. The chapter examines the different steps of a robust watermarking scenario for color images, as well as the algorithms used to adapt the index modulation Lattice method. Quaternions can be a tool to manipulate color, which explains the different works offering quaternion-based watermarking. The chapter discusses a psychovisual model that makes the choice of direction as adaptive as possible, that is, it shows how to determine the optimal direction vectors for any RGB color. It explores the modeling part and its application for color watermarking and uses a chromatic discrimination ellipsoid model based on the Naka-Rushton law of photoreceptor dynamics.