1. A method comprising: partitioning an image into a first plurality of image segments, of which a first image segment includes a first plurality of image pixels; partitioning the image into a second plurality of image segments, of which a second image segment includes a second plurality of image pixels; estimating a grey value for an image pixel of the first and second plurality of image segments; estimating mean and standard deviations of the grey value of the image pixel; and assigning a first grey membership parameter to the image pixel having the standard deviation below the pre-determined threshold and assigning a second grey membership parameter to the image pixel having the standard deviation above the pre-determined threshold.