www.pudn.com > wenlituxiangjiansuo.rar > coldfilt.m

function Y = coldfilt(X, ha, hb) 
 
% function Y = coldfilt(X, ha, hb) 
% Filter the columns of image X using the two filters ha and hb = reverse(ha). 
% ha operates on the odd samples of X and hb on the even samples. 
% Both filters should be even length, and h should be approx linear phase with 
% a quarter sample advance from its mid pt (ie |h(m/2)| > |h(m/2 + 1)|). 
% 
%                   ext        top edge                     bottom edge       ext 
% Level 1:        !               |               !               |               ! 
% odd filt on .    b   b   b   b   a   a   a   a   a   a   a   a   b   b   b   b    
% odd filt on .      a   a   a   a   b   b   b   b   b   b   b   b   a   a   a   a 
% Level 2:        !               |               !               |               ! 
% +q filt on x      b       b       a       a       a       a       b       b        
% -q filt on o          a       a       b       b       b       b       a       a 
% 
% The output is decimated by two from the input sample rate and the results 
% from the two filters, Ya and Yb, are interleaved to give Y. 
% Symmetric extension with repeated end samples is used on the composite X 
% columns before each filter is applied. 
% 
% Cian Shaffrey, Nick Kingsbury 
% Cambridge University, August 2000 
 
[r,c] = size(X); 
if rem(r,4) > 0, error('No. of rows in X must be a multiple of 4!'); end 
m = length(ha); 
if m ~= length(hb), error('Lengths of ha and hb must be the same!'); end 
if rem(m,2) > 0, error('Lengths of ha and hb must be even!'); end 
m2 = fix(m/2); 
 
% Set up vector for symmetric extension of X with repeated end samples. 
xe = reflect([(1-m):(r+m)], 0.5, r+0.5); % Use 'reflect' so d < m works OK. 
 
% Select odd and even samples from ha and hb. 
hao = ha(1:2:m); 
hae = ha(2:2:m); 
hbo = hb(1:2:m); 
hbe = hb(2:2:m); 
t = [6:4:(r+2*m-2)]; 
 
r2 = r/2; 
Y = zeros(r2,c); 
if sum(ha.*hb) > 0, 
   s1 = 1:2:r2;  
   s2 = s1 + 1; 
else 
   s2 = 1:2:r2;  
   s1 = s2 + 1; 
end 
 
% Perform filtering on columns of extended matrix X(xe,:) in 4 ways.  
Y(s1,:) = conv2(X(xe(t-1),:),hao(:),'valid') + conv2(X(xe(t-3),:),hae(:),'valid'); 
Y(s2,:) = conv2(X(xe(t),:),hbo(:),'valid') + conv2(X(xe(t-2),:),hbe(:),'valid'); 
 
return