measerr() function keeps returning an error for which ever type of image i pass to it

measerr() function keep complaining of data type whenever i pass an image to it, what type of image does it accept exaclty??.. any help rendered will be greatly appreciated!!..Thanks

[Gaffar kasumu]

i noticed the problem is not the function, its because the function is not installed on my matlab installation at all. How do i install this function?