How to use graydiffweight() ?

To fuse an image i want to calculate weight for the image. when i use the following line in matlab i am getting error. My image size is c=576,r=1485 My question is: How to calculate weight of the image that will be range from (0-1)? c=67;r=159; w= graydiffweight(s1,c, r,'GrayDifferenceCutoff',25);