If i change the image except rice.png it shows me the filter 2 error?

str ='Hello'
A = double(str)
I1=mat2gray(A)

J=filter2(fspecial('sobel'),I1);
min_matrix=min(J(:))
max_matrix = max(J(:))

K = mat2gray(J);
min_image = min(K(:))
max_image = max(K(:))
figure
imshow(K)

Am getting an below error and the image pears.png is also not changed into gray scale image.. Please help

[Jan]

Please post error messages as text, not as screenshot. Thanks.

[Guillaume]

I've formatted your post for you but please use the {}Code button to do this yourself in the future.

What has 'rice.png' or 'pears.png' got to do with any of the code you've posted?

Your code works without error for me (It also doesn't do anything useful but that's another matter entirely). I would suspect that you have some path issues, although I don't understand how matlab could find the fspecial function but not the conv2 function. Which version of matlab are you using?