You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: dftregistration.m
    path of file: ./repos/ciatah/_external_programs/_file_exchange/efficient_subpixel_registration
    
    the code of the file until where you have to start completion: 

function [output Greg] = dftregistration(buf1ft,buf2ft,usfac)
% function [output Greg] = dftregistration(buf1ft,buf2ft,usfac);
% Efficient subpixel image registration by crosscorrelation. This code
% gives the same precision as the FFT upsampled cross correlation in a
% small fraction of the computation time and with reduced memory 
% requirements. It obtains an initial estimate of the crosscorrelation peak
% by an FFT and then refines the shi
    
function out=dftups(in,nor,noc,usfac,roff,coff)
% function out=dftups(in,nor,noc,usfac,roff,coff);
% Upsampled DFT by matrix multiplies, can compute an upsampled DFT in just
% a small region.
% usfac         Upsampling factor (default usfac = 1)
% [nor,noc]     Number of pixels in the output upsampled DFT, in
%               units of upsampled pixels (default = size(in))
% roff, coff    Row and column offsets, allow to shift the output array to
%               a region of interest on the DFT (default = 0)
% Recieves DC in upper left corner, image center must be in (1,1) 
% Manuel Guizar - Dec 13, 2007
% Modified from dftus, by J.R. Fienup 7/31/06

% This code is intend