www.pudn.com > MatlabSIFTcode_1.rar > affine.m

function img2 = affine(img, r, sx, sy, a, b, xo, yo) 
 
R = [cos(r) -sin(r) 0;  
     sin(r) cos(r)  0;  
     0      0       1]; 
  
S = [sx  a   0; 
     b  sy   0; 
     0   0   1]; 
  
T2 = [1  0  -xo; 
      0  1  -yo; 
      0  0   1]; 
   
T1 = [1  0  xo; 
      0  1  yo; 
      0  0  1]; 
 
A = T1*R*S*T2; 
 
[h,w]=size(img); 
 
[x,y] = meshgrid(1:h,1:w); 
x=x(:); 
y=y(:); 
 
XP = [x';y';ones(1,length(x))]; 
 
X = A*XP; 
 
z = find(X(1,:)>w-1); 
X(1,z) = w-1; 
 
z = find(X(1,:)<=1); 
X(1,z) = 1.5; 
 
z= find(X(2,:)>h-1); 
X(2,z) = h-1; 
 
z= find(X(2,:)<1.5); 
X(2,z) = 1.5; 
 
x = X(1,:); 
y = X(2,:); 
 
alpha = x - floor(x);   %calculate alphas and betas for each point 
beta = y - floor(y); 
 
fx = floor(x);   fy = floor(y); 
 
inw = fy + (fx-1)*h;    %create index for neighboring pixels 
ine = fy + fx*h; 
isw = fy+1 + (fx-1)*h; 
ise = fy+1 + fx*h; 
 
img2 = (1-alpha).*(1-beta).*img(inw) + ...  %interpolate 
       (1-alpha).*beta.*img(isw) + ... 
       alpha.*(1-beta).*img(ine) + ... 
       alpha.*beta.*img(ise); 
 
img2 = reshape(img2,h,w); 
 
imagesc(img2);