function y = daubech4( x )
% DAUBECH4 4 tap Daubechies wavelet kernel

c0 = 0.4829629;
c1 = 0.8365163;
c2 = 0.2241439;
c3 = -0.1294095;

d_kernel_l = [ c0 c1 c2 c3 ];
d_kernel_h = [ c3 -c2 c1 -c0 ];

[ size_v, size_h ] = size( x );
boundary = size_h - 3;
half = size_h / 2;

%  Convolve with the filter kernels
z = [ 1:size_h ];
for start = 1:2:size_h
	if( start <= boundary )
		a = x( start:start+3 );
	else
		residual = (size_h - start) + 1;
		a( 1:residual ) = x( start:size_h );
		a( residual+1:4 ) = x( 1:4-residual );
	end
	z( start ) = a * d_kernel_l';
	z( start + 1 ) = a * d_kernel_h';
end

%  Shuffle the data into a temporary vector
y = [ 1:size_h ];
y( 1:1:half ) = z( 1:2:size_h );
y( half+1:1:size_h ) = z( 2:2:size_h );