MATLAB: Imfilter and filter2

filter2imfilter

Hi guys,

Are imfilter and fiter2 the same for two dimensional array?

I did a lot of experiment. It seems they are the same. But filter2 are much faster than imfilter

Thanks,

Zhong

Yes, they are the same in some instances:

    h = 1/100*ones(10,10);
    x = randn(20,20);
    y = filter2(h,x);
    y1 = imfilter(x,h);
    max(abs(y(:)-y1(:)))

but imfilter() gives more options to specify boundary conditions for example and whether to rotate the kernel or not -- 'corr' vs 'conv'

imresize(your_image,512/511)

Zhang, the difference is that there is a rotation of the kernel by 180 degrees (pi radians) between the two.

So for:

   h = [1     2     3
       4     5     6
       7     8     9];

and

   h1 = [9 8 7
           6 5 4
           3 2 1];
 x = randn(20,20);
 isequal(imfilter(x,h,'corr'),imfilter(x,h1,'conv'))

returns a 1.