1. A method for estimating an average background value and an average foreground value of an image data formed by a plurality of pixels, the method comprising: selecting a first plurality of pixels forming a first calculation window from the plurality of pixels; determining at least first, second and third statistical moments for the first plurality of pixels; and determining at least one of average background value and average foreground value using the at least first, second and third statistical moments determined for the first plurality of pixels.