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: vl_imwbackward.m
    path of file: ./repos/panorama/lib/vlfeat-0.9.20/toolbox/imop
    
    the code of the file until where you have to start completion: function [wI,wIx,wIy] = vl_imwbackward(varargin)
% VL_IMWBACKWARD  Image backward warping
%   J = VL_IMWBACKW
    
function
%   INTERP2(), but it is significantly faster.
%
%   See also: IMWFORWARD(), INTERP2(), VL_HELP().

% Copyright (C) 2007-12 Andrea Vedaldi and Brian Fulkerson.
% All rights reserved.
%
% This file is part of the VLFeat library and is made available under
% the terms of the BSD license (see the COPYING file).

if nargin < 5
  I = varargin{1} ;
  [M,N,K] = size(I) ;
  xr = 1:N ;
  yr = 1:M ;
  varargin = { varargin{2:end