A subjective image quality metric for bit-inversion-based watermarking

An image watermarking scheme using the previously proposed bit embedding method is developed. To achieve a desired subjective visual quality in the watermarked image, the embedding parameter that is related to both the image quality and the embedding capacity is determined by using a perceptual model. First, based on the properties of the bit embedding method, the perceptual model of two kinds of objective quality measures is assumed. Then, the measurements of human subjective image quality are analyzed from the viewpoint of the correlation with these two measures. Thereby, the estimating function that can yield an estimate of the subjective quality from two objective measurements is determined. According to the estimating function, the bit embedding method performs in each image region so as to achieve a desired subjective image quality while increasing the capacity of embedding watermark bits. The simulation results demonstrate that the estimating function values have a linear correlation with human subjective evaluations, and the embedding parameters can be adaptively changed in every image region by using the function.