facing error in isa()

i am writing this gabor filter code and when i run it than an error comes which is as follow....

% gabor main interface
clc
img = imread('\C:\Users\Asad\Documents\MATLAB\CE.bmp');
I=rgb2gray(img);
info(I)
[G,gabout] = gaborfilter1(I,.9,10,16,pi/3);

% gaborfilter1.m

function [G,gabout] = gaborfilter(I,Sx,Sy,f,theta);
if isa(I,'double')~=1

Error:--
??? Input argument "I" is undefined.

Error in ==> gaborfilter at 5
if isa(I,'double')~=1

I = double(I);
end

Answer 1

[Walter Roberson]

This seems odd, unless you tried to run gaborfilter by itself instead of running the "gabor main interface" file.