Computing watermark capacity in images according to their quad tree

Abstract

Determining the capacity of watermark for images is a complex task. This capacity may be influenced by many factors such as the content of image and also the strength of watermark. In some recent works the image content has been considered for calculation of watermark capacity. One such approach is to use the noise visibility function (NVF) introduced in (Voloshynovsky, et al., 1999). In this paper we introduced a new method for finding NVF according to the quad tree representation of image instead of using pixel neighborhood data. Our experimental results showed that the depth of a pixel in image quad tree represents much information about the pixel and its maximum allowable distortion compared to pixel neighborhood data as used by the existing NVF computing method. Our method for determining NVF, gave similar results for image capacity compared to the approach based on original NVF calculation as given in (F. Zhang and H. Zhang, June 2004)