window2d.m

介绍了傅立叶变换的基本原理

function w=window2d(p,q,wtype,param) 
> USAGE: w=window2d(p,q,wtype,param) 
> return 2-dimensional hamming window 
> 
> centred on (p/2,q/2) 
> (p,q) = dimensions of window 
> 
> (height,width) = dimensions of image to be applied to... 
> 
> TYPES are BARTLETT, BLACKMAN, BOXCAR, CHEBWIN, HAMMING, HANN and KAISER 
> 
> Adam Wilmer, October 2002 

> disp('HAMMING2 : check that this is actually a proper 2-dimensional Hamming window...') 

w = zeros(p,q); 

switch lower(wtype) 
case 'none' 
w = ones(p,q); 
case 'bartlett' 
wlp = bartlett(p); 
wlq = bartlett(q); 
w = wlp(:) * wlq(:).'; > Outer product 

case 'blackman' 
wlp = blackman(p); 
wlq = blackman(q); 
w = wlp(:) * wlq(:).'; > Outer product 

case 'boxcar' 
wlp = boxcar(p); 
wlq = boxcar(q); 
w = wlp(:) * wlq(:).'; > Outer product 

case 'chebwin' 
if (nargin==4) 
r = param; > this is the desired sidelobe attenuation in dB 
else 
r=100; 
end 
w1p = chebwin(p,r); > Some 1D window 
w1q = chebwin(q,r); 
w = w1p(:) * w1q(:).'; > Outer product 

case 'hamming' 
w1p = hamming(p); > Some 1D window 
w1q = hamming(q); 
w = w1p(:) * w1q(:).'; > Outer product 

case 'hann' 
w1p = hann(p); > Some 1D window 
w1q = hann(q); 
w = w1p(:) * w1q(:).'; > Outer product 

case 'kaiser' 
if (nargin==4) 
beta = param; > this is the desired sidelobe attenuation in dB 
else 
beta=10; 
end 
w1p = kaiser(p,beta); > Some 1D window 
w1q = kaiser(q,beta); 
w = w1p(:) * w1q(:).'; > Outer product 

case 'triang' 
w1p = triang(p); > Some 1D window 
w1q = triang(q); 
w = w1p(:) * w1q(:).'; > Outer product 

case('hann_rotational') > use a rotationally symmetric type window 
if (p~=q) 
disp('cannot use rotational-type window for non-square images at present...') 
end 
p 
N = p; 
w=hann(N); 
M = (N-1) / 2; 
n = 2 / M * (-M:M); 
[x,y] = meshgrid(n); 
r = sqrt( x.^2 + y.^2 ); 
w_2D = zeros(N); 
size(n) 
size(w) 
size(r) 

w_2D(:) = interp1(n, w, r(:)); 
w_2D(isnan(w_2D)) = 0; 
w = w_2D; 

otherwise 
disp('Window choice (',wtype,')is not recognised -- choose another...') 
help window2d; 
return; 
end 

>figure,mesh(w),title(['The ',wtype,' window function.'])