transformimage.m

介绍了傅立叶变换的基本原理

function [r,g,b] = transformImage(A,Ar,Ac,Nrho,Ntheta,Method,Center,Shape) 
> Inputs: A the input image 
> Nrho the desired number of rows of transformed image 
> Ntheta the desired number of columns of transformed image 
> Method interpolation method (nearest,bilinear,bicubic) 
> Center origin of input image 
> Shape output size (full,valid) 
> Class storage class of A 

global rho; 

theta = linspace(0,2*pi,Ntheta+1); theta(end) = []; 

switch Shape 
case 'full' 
corners = [1 1;Ar 1;Ar Ac;1 Ac]; 
d = max(sqrt(sum((repmat(Center(:)',4,1)-corners).^2,2))); 
case 'valid' 
d = min([Ac-Center(1) Center(1)-1 Ar-Center(2) Center(2)-1]); 
end 
minScale = 1; 
rho = logspace(log10(minScale),log10(d),Nrho)'; > default 'base 10' logspace - play with d to change the scale of the log axis 

> convert polar coordinates to cartesian coordinates and center 
xx = rho*cos(theta) + Center(1); 
yy = rho*sin(theta) + Center(2); 

if nargout==3 
if strcmp(Method,'nearest'), > Nearest neighbor interpolation 
r=interp2(A(:,:,1),xx,yy,'nearest'); 
g=interp2(A(:,:,2),xx,yy,'nearest'); 
b=interp2(A(:,:,3),xx,yy,'nearest'); 
elseif strcmp(Method,'bilinear'), > Linear interpolation 
r=interp2(A(:,:,1),xx,yy,'linear'); 
g=interp2(A(:,:,2),xx,yy,'linear'); 
b=interp2(A(:,:,3),xx,yy,'linear'); 
elseif strcmp(Method,'bicubic'), > Cubic interpolation 
r=interp2(A(:,:,1),xx,yy,'cubic'); 
g=interp2(A(:,:,2),xx,yy,'cubic'); 
b=interp2(A(:,:,3),xx,yy,'cubic'); 
else 
error(['Unknown interpolation method: ',method]); 
end 
> any pixels outside , pad with black 
mask= (xx>Ac) | (xx<1) | (yy>Ar) | (yy<1); 
r(mask)=NaN; 
g(mask)=NaN; 
b(mask)=NaN; 
else 
if strcmp(Method,'nearest'), > Nearest neighbor interpolation 
r=interp2(A,xx,yy,'nearest'); 
elseif strcmp(Method,'bilinear'), > Linear interpolation 
r=interp2(A,xx,yy,'linear'); 
elseif strcmp(Method,'bicubic'), > Cubic interpolation 
r=interp2(A,xx,yy,'cubic'); 
else 
error(['Unknown interpolation method: ',method]); 
end 
> any pixels outside warp, pad with black 
mask= (xx>Ac) | (xx<1) | (yy>Ar) | (yy<1); 
r(mask)=NaN; 
end