Source code for vl_demo_sift_basic.m

This file is located in the toolbox/demo folder in VLFeat package.

% VL_DEMO_SIFT_BASIC  Demo: SIFT: basic functionality

pfx = fullfile(vl_root,'figures','demo') ;
randn('state',0) ;
rand('state',0) ;
figure(1) ; clf ;

% --------------------------------------------------------------------
%                                                        Load a figure
% --------------------------------------------------------------------
I = imread(fullfile(vl_root,'data','roofs1.jpg')) ;

image(I) ; colormap gray ;
axis equal ; axis off ; axis tight ;
vl_demo_print('sift_basic_0') ;

% --------------------------------------------------------------------
%                                       Convert the to required format
% --------------------------------------------------------------------
I = single(rgb2gray(I)) ;

clf ; imagesc(I)
axis equal ; axis off ; axis tight ;
vl_demo_print('sift_basic_1') ;

% --------------------------------------------------------------------
%                                                             Run SIFT
% --------------------------------------------------------------------
[f,d] = vl_sift(I) ;

hold on ;
perm = randperm(size(f,2)) ;
sel  = perm(1:50) ;
h1   = vl_plotframe(f(:,sel)) ; set(h1,'color','k','linewidth',3) ;
h2   = vl_plotframe(f(:,sel)) ; set(h2,'color','y','linewidth',2) ;

vl_demo_print('sift_basic_2') ;

delete([h1 h2]);

h3 = vl_plotsiftdescriptor(d(:,sel),f(:,sel)) ;
set(h3,'color','k','linewidth',2) ;
h4 = vl_plotsiftdescriptor(d(:,sel),f(:,sel)) ;
set(h4,'color','g','linewidth',1) ;
h1   = vl_plotframe(f(:,sel)) ; set(h1,'color','k','linewidth',3) ;
h2   = vl_plotframe(f(:,sel)) ; set(h2,'color','y','linewidth',2) ;

vl_demo_print('sift_basic_3') ;

% --------------------------------------------------------------------
%                                                      Custom keypoint
% --------------------------------------------------------------------
clf ; imagesc(I(1:200,1:200,:))
axis equal ; axis off ; axis tight ;
hold on;

fc = [100;100;10;-pi/8] ;
[f,d] = vl_sift(I,'frames',fc) ;

h3   = vl_plotsiftdescriptor(d,f) ;  set(h3,'color','k','linewidth',3) ;
h4   = vl_plotsiftdescriptor(d,f) ;  set(h4,'color','g','linewidth',2) ;
h1   = vl_plotframe(f) ; set(h1,'color','k','linewidth',4) ;
h2   = vl_plotframe(f) ; set(h2,'color','y','linewidth',2) ;

vl_demo_print('sift_basic_4') ;

% --------------------------------------------------------------------
%                                   Custom keypoints with orientations
% --------------------------------------------------------------------

fc = [100;100;10;0] ;
[f,d] = vl_sift(I,'frames',fc,'orientations') ;

delete([h1 h2 h3 h4]) ;

h3   = vl_plotsiftdescriptor(d,f) ;  set(h3,'color','k', 'linewidth',3) ;
h4   = vl_plotsiftdescriptor(d,f) ;  set(h4,'color','g', 'linewidth',2) ;
h1   = vl_plotframe(f) ; set(h1,'color','k','linewidth',4) ;
h2   = vl_plotframe(f) ; set(h2,'color','y','linewidth',2) ;

vl_demo_print('sift_basic_5') ;