add function

matlab/tfgm/scripts/get_mask_area.m

+function [mask_area, varargout] = get_mask_area(mask)
+%compute mask area
+
+mask_area = sum(mask(:));
+mask_area_ratio = mask_area/ (size(mask,1)*size(mask,2));
+ varargout{1} = mask_area_ratio;
+       
+end
+
+