fftn code fails

[Terry Duell]

Hello All,
I am investigating some code which is said to run in Matlab, but throws an  
error in Octave 3.6.4 (Fedora 19 x86_64).

we have an image, "g", [254,254,3], and an array, "H", [9,9], as follows;

[row col frame] = size(g)
row =  254
cols =  254
frames =  3

size(H)
ans =

   9   9

When I call fftn, as per the Matlab code, I get an error, thus;

fftn(H, [row col frame])
error: fftn: SIZE must be a vector of length dim

Is our fftn incompatible with the Matlab fftn?
If one can't use fftn in the manner shown above, how does one handle  
arrays such as the image in this example?
Do we have to process each 2D layer (ie [254,254]) separately with fft2  
and then combine later into a  [254,254,3] result?

Cheers,
--
Regards,
Terry Duell