8 Adjusted-Purpose Watermarking
Frank Y. Shih · 2017
This chapter focuses on high-capacity watermarking techniques, including robust watermarking and high-capacity, multiple-regions-of-interest watermarking for medical images. It explores multiple region of noninterest (RONI) medical image watermarking and proposes a novel scheme to achieve high data capacity and high image quality in the frequency domain. The chapter adopts an encryption method by taking a logarithm of ASCII codes for the purpose of robustness. Zhao presented a robust wavelet domain watermarking algorithm based on chaotic maps. Frequency domain watermarking is robust because the embedded messages are spread all over the spatial extent of the image. During spatial frequency transformation, the low frequencies in the transformed domain reflect the smooth areas of an image, and the high frequencies reflect areas with high intensity changes, such as edges and noise. In order to enlarge the watermark capacity, the chapter adopts a chaotic map to break the local spatial similarity of an image so it can generate more significant coefficients in the transformed domain.