Implementations of HVS Models in Digital Image Watermarking
P. Foris, Dušan Levický · Brno University of Technology Digital Library (Brno University of Technology) · 2007
Abstract. In the paper two possible implementations of Human Visual System (HVS) models in digital watermark-ing of still images are presented. The first method performs watermark embedding in transform domain of Discrete Cosine Transform (DCT) and the second method is based on Discrete Wavelet Transform (DWT). Both methods use HVS models to select perceptually significant transform coefficients and at the same time to determine the bounds of modification of selected coefficients in watermark em-bedding process. The HVS models in DCT and DWT do-mains consist of three parts which exploit various proper-ties of human eye. The first part is the HVS model in DCT (DWT) domain based on three basic properties of human vision: frequency sensitivity, luminance sensitivity and masking effects. The second part is the HVS model based on Region of Interest (ROI). It is composed of contrast thresholds as a function of spatial frequency and eye’s eccentricity. The third part is the HVS model based on noise visibility in an image and is described by so called Noise Visibility Function (NVF). Watermark detection is performed without use of original image and watermarks have a form of real number sequences with normal distri-bution zero mean and unit variance. The robustness of presented perceptual watermarking methods against vari-ous types of attacks is also briefly discussed. Keywords Digital image watermarking, human visual system models, discrete cosine transform, discrete wavelet transform, noise visibility function, watermark em-bedding, watermark detection. 1.