GMS matching strategy (video)

This sample demonstrates the GMS matching strategy.

Sources:

Options

opts = struct();
opts.nfeatures = 2500;
opts.fastThreshold = 20;
opts.drawSimple = true;
opts.withRotation = false;
opts.withScale = false;

% helper function
siz = @(img) [size(img,2), size(img,1)];

create feature detector and descriptor matcher objects

detector = cv.ORB('MaxFeatures',opts.nfeatures, 'FastThreshold',opts.fastThreshold);
matcher = cv.DescriptorMatcher('BruteForce-Hamming');

initialize camera

cap = createVideoCapture(0);
assert(cap.isOpened());
frame = cap.read();
assert(~isempty(frame));

prepare UI

hImg = imshow(cat(2,frame,frame));
title('Matches GMS')
hFig = ancestor(hImg, 'figure');
setappdata(hFig, 'flag',false);
hBtn = uicontrol('Parent',hFig, 'Style','pushbutton', ...
    'Position',[20 20 150 20], 'String','Set reference frame', ...
    'Callback',@(~,~) setappdata(hFig, 'flag',true));

Main loop

disp('Press button to reinitialize the reference image.')
disp('Close figure to quit.')
tsec = zeros(3,1);
[frameRef, kpRef, descRef] = deal([]);
while ishghandle(hFig)
    % read frame
    frame = cap.read();
    if isempty(frame), break; end

    % reference frame
    if isempty(frameRef)
        frameRef = frame;
        [kpRef, descRef] = detector.detectAndCompute(frameRef);
    end

    % detect keypoints and compute descriptors
    tic();
    [kp, desc] = detector.detectAndCompute(frame);
    tsec(1) = toc();

    % match descriptors
    tic();
    matchesAll = matcher.match(desc, descRef);
    tsec(2) = toc();

    % GMS matching
    tic();
    matchesGMS = cv.matchGMS(siz(frame), kp, siz(frameRef), kpRef, matchesAll, ...
        'WithRotation',opts.withRotation, 'WithScale',opts.withScale);
    tsec(3) = toc();

    % show GMS matches
    out = cv.drawMatches(frame, kp, frameRef, kpRef, matchesGMS, ...
        'NotDrawSinglePoints',opts.drawSimple);

    % display results
    str = {
        sprintf('ORB: %.2f ms', tsec(1)*1000)
        sprintf('Matching: %.2f ms', tsec(2)*1000)
        sprintf('GMS matching: %.2f ms', tsec(3)*1000)
    };
    for i=1:numel(str)
        out = cv.putText(out, str{i}, [20 20*i], 'FontScale',0.5, 'Color',[255 0 0]);
    end
    set(hImg, 'CData',out)
    drawnow

    % check if button was pressed
    flag = ishghandle(hFig) && getappdata(hFig, 'flag');
    if flag
        setappdata(hFig, 'flag',false);
        frameRef = [];  % reset reference frame for next iteration
    end
end
cap.release();

Press button to reinitialize the reference image.
Close figure to quit.