SIFT.m

clc;
% Extract SIFT Features

%% Select Scene image
[scene_name, file_path] = uigetfile('*.*', 'Select the scene image');
scene_img_path = sprintf("%s%s", file_path, scene_name);
if scene_name
    scene_img = imread(scene_img_path);
    scene_img_gray = single(im2gray(scene_img));
else
    disp('No scene image selected!');
    return
end

%% Single image SIFT feature extraction
figure('Name', 'SIFT frames & descriptors', 'NumberTitle', 'off');
imshow(scene_img); % Display image

% Compute the SIFT frames (keypoints) and descriptors
[f,d] = vl_sift(scene_img_gray);
perm = randperm(size(f, 2));
sel = perm(1:50);
h1 = vl_plotframe(f(:, sel));
h2 = vl_plotframe(f(:, sel));
set(h1, 'color', 'k', 'linewidth', 3);
set(h2, 'color', 'y', 'linewidth', 2);
h3 = vl_plotsiftdescriptor(d(:,sel), f(:,sel));
set(h3,'color','g');

%% Select Target image
% Either pick a new image or rotate the scene image
% For rotating the scene image, uncomment the line below
% target_img = imresize(imrotate(scene_img, -20), 1.2);
% For picking the a new target image
[target_name, file_path] = uigetfile('*.*', 'Select the target image');
target_path = sprintf("%s%s", file_path, target_name);
if target_name
    target_img = imread(target_path);
else
    disp('No target image selected!');
    return
end

figure('Name', 'Selected Images', 'NumberTitle', 'off');
subplot(1,2,1); imshow(scene_img);  % Display scene image
title(sprintf('Scene image\n%s', scene_name));


%% Image Matching

% --- Resize target image ---
% scene_img_size = size(scene_img);
% target_img_size = scene_img_size(1:2);    % => size(scene_img_gray)
target_img = imresize(target_img, size(scene_img_gray));
subplot(1,2,2); imshow(target_img); % Display target image
title(sprintf('Target image\n%s', target_name));
target_img_gray = single(im2gray(target_img));

% --- NOTE: Images have to be the same size ---
[fs, ds] = vl_sift(scene_img_gray);
[ft, dt] = vl_sift(target_img_gray);
[matches, scores] = vl_ubcmatch(ds, dt);

%% Visualization
figure('Name', 'Image Matching Visulization', 'NumberTitle', 'off');
ax = axes;
m1 = fs(1:2,matches(1,:));
m2 = ft(1:2,matches(2,:));
m2(1,:) = m2(1,:) + size(scene_img_gray,2) * ones(1,size(m2,2));
X = [m1(1,:);m2(1,:)];
Y = [m1(2,:);m2(2,:)];
c = [scene_img target_img];
imshow(c,[]); 
hold on;

% Determine number of lines depending on dimensions of X and Y
line(ax, X, Y);