index exceeds matrix dimension

Hi i tried this code but it says that index exceeds matrix dimensoin

fgx=fg(:,1);% Foreground or object pixels
fgy=fg(:,2);

for i = 1:size(fgx,1)
    obj_pixels(i)=im(fgx(i),fgy(i));% Extract values of foreground pixels
end

sizes:

size(fgx)=10941x1
size(fgy)=10941x1
size(fgx,1)=10941
i=129

i don't know why i is stoped only on 129

thanks in advance

[Adam]

Without being able to run the code I suspect that the index that is exceeding the matrix dimension is not 'i' as an index to fgx or fgy, but the result of fgx(i) or fgy(i) exceeds the dimensions of 'im' when you try to index into it using these.

What is the size of 'im' and what are the values of fgx(129) and fgy(129)?