www.pudn.com > MatlabSIFT.zip > build_pyramid.m

%///////////////////////////////////////////////////////////////////////////////////////////// 
% 
% build_pyramid - build scaled image pyramid and difference of gaussians pyramid 
% 
% Usage:  [pyr,imp] = build_pyramid(img,levels,scl); 
% 
% Parameters:   
%             
%            img :      original image 
%            levels :   number of levels in pyramid 
%            scl :      scaling factor between pyramid levels 
% 
% Returns: 
% 
%            pyr :      difference of gaussians filtered image pyramid 
%            imp :      image pyramid cell array 
% 
% Author:  
% Scott Ettinger 
% scott.m.ettinger@intel.com 
% 
% May 2002 
%///////////////////////////////////////////////////////////////////////////////////////////// 
 
function [pyr,imp] = build_pyramid(img,levels,scl) 
 
img2 = img; 
img2 = resample_bilinear(img2,1/2);         %expand to retain spatial frequencies 
 
%img2 = imresize(img2,2,'bilinear');         %expand to retain spatial frequencies 
 
sigma=1.5;    %variance for laplacian filter 
sigma2=1.5;   %variance for downsampling 
 
sig_delta = (1.6-.6)/levels; 
 
 
for i=1:levels 
         
     if i==1 
         img3 = img2; 
         img2 = filter_gaussian(img2,7,.5); %slightly filter bottom level 
     end 
         
     imp{i}=img2; 
     A = filter_gaussian(img2,7,sigma);    %calculate difference of gaussians 
     B = filter_gaussian(A,7,sigma); 
     pyr{i} = A-B;                         %store result in cell array 
      
     if i==1 
         img2 = img3; 
     else 
         B = filter_gaussian(img2,7,sigma2);    %anti-alias for downsampling 
         B = filter_gaussian(B,7,sigma2); 
     end 
      
     img2 = resample_bilinear(B,scl);       %downsample for next level 
      
end 
 
%show_pyramid(pyr)  %show pyramid if desired 
 
%/////////////////////////////////////////////////////////////////////////////// 
function show_pyramid(pyr) 
 
    close all 
 
    [h,w] = size(pyr); 
    for i=1:w 
     
        figure 
        imagesc(pyr{i}); 
        colormap gray; 
    end