Expand Variance Mean sorting for Reversible Watermarking

Prediction Error Expansion is one of Reversible Watermarking (RW) techniques that gives effective results and has been continuously developed over the years. Among those techniques, Sorting Absolute Prediction Error (APE) is an important step used to reduce image distortion; so in this research we focus on developing the technique of sorting APE in ascending order more accurately. We can use local variance values in predicting APE and these values are calculated from means so they are suitable for predicting which areas contains high or low APE values. Consequently, we have improved this parameter by using Expand Variance Mean which can increase efficiency of sorting process and raise PSNR values.