function[dpf,GW,err] = optconv(F,roi,G,sig,max) 

[row,col] = size(F);
[Mx,My] = meshgrid(1:col,1:row);
inds = find(roi);
G = G;

err(1) = norm( G(inds) - F(inds));

dpf = optflow(F,roi,G,sig)

GW = interp2(Mx,My,G,Mx-dpf(1),My-dpf(2), 'bilinear');

err(2) = norm( GW(inds) - F(inds) );
c = 1;
while ( c <= max ) 

  dpi = optflow(F,roi,GW,sig);
  dpf = dpf + dpi;
  GW = interp2(Mx,My,G,Mx-dpf(1), My-dpf(2), 'bilinear');  

  err(c+2) = norm( GW(inds) - F(inds) );
%  imagesc(roi.*(GW-F),[-2,2]);
%  con = input('iterate ...');
  c = c+1;
  if ( c == max / 2 ) 
    sig = sig * 0.5;
  end
end