8. The method of claim 1 , wherein the plurality of focus classification features comprises at least one focus classification feature that is insensitive to the spatial distribution of the pixel intensity variations in the image.
8. The method of claim 1 , wherein the plurality of focus classification features comprises at least one focus classification feature that is insensitive to the spatial distribution of the pixel intensity variations in the image. 9. The method of claim 8 , wherein the focus classification feature that is insensitive to the spatial distribution associated with the pixel intensity variations in the image is selected from a group of focus classification features that are image pixel intensity statistical distribution parameters.