motiur's profile - activity

I am trying to recode feature matching and homography using mexopencv .Mexopencv ports OpenCV vision toolbox into Matlab .

My code in Matlab using OpenCV toolbox:

function hello
    disp('Feature matching demo. Press any key when done.');

    % Set up camera
    camera = cv.VideoCapture;
    pause(3); % Necessary in some environment. 

    % Set up display window
    window = figure('KeyPressFcn',@(obj,evt)setappdata(obj,'flag',true));
    setappdata(window,'flag',false);

    object = imread('D:/match.jpg');

    %Conversion from color to gray
    object = cv.cvtColor(object,'RGB2GRAY');

    %Declaring detector and extractor
    detector = cv.FeatureDetector('SURF');
    extractor = cv.DescriptorExtractor('SURF');

    %Calculating object keypoints
    objKeypoints = detector.detect(object);

    %Calculating object descriptors
    objDescriptors = extractor.compute(object,objKeypoints);

    % Start main loop
    while true
        % Grab and preprocess an image
        im = camera.read;
        %im = cv.resize(im,1);
        scene = cv.cvtColor(im,'RGB2GRAY');

        sceneKeypoints = detector.detect(scene);

        if length(sceneKeypoints) < 2 
            continue
        end;

        sceneDescriptors = extractor.compute(scene,sceneKeypoints);

        matcher = cv.DescriptorMatcher('BruteForce');
        matches = matcher.match(objDescriptors,sceneDescriptors);

        objDescriptRow = size(objDescriptors,2);
        dist_arr = zeros(1,objDescriptRow);

        for i=1:objDescriptRow
            dist_arr(i) = matches(i).distance;
        end;

        min_dist = min(dist_arr);

        N = 10000;    
        good_matches = repmat(struct('distance',0,'imgIdx',0,'queryIdx',0,'trainIdx',0), N, 1 );

        goodmatchesSize = 0;

        for i=1:objDescriptRow
            if matches(i).distance < 3 * min_dist
                good_matches(i).distance = matches(i).distance;
                good_matches(i).imgIdx = matches(i).imgIdx;
                good_matches(i).queryIdx = matches(i).queryIdx;
                good_matches(i).trainIdx = matches(i).trainIdx;
                goodmatchesSize = goodmatchesSize +1;
            end
        end

        im_matches = cv.drawMatches(object, objKeypoints, scene, sceneKeypoints,good_matches);

        objPoints = [];
        scnPoints = [];

        for i=1:goodmatchesSize

            qryIdx = good_matches(i).queryIdx;
            trnIdx = good_matches(i).trainIdx;
            if qryIdx == 0 
                continue 
            end;
            if trnIdx == 0
                continue
            end;

            first_point = objKeypoints(qryIdx).pt;
            second_point = sceneKeypoints(trnIdx).pt;

            objPoints(i,:)= (first_point);

            scnPoints(i,:) = (second_point);

        end

        H = cv.findHomography(objPoints,scnPoints);

        objectCorners = [];
        sceneCorners = zeros(4,2);

        for i=1:4
            for j=1:2
                sceneCorners(i,j) = 0;
            end;
        end;

        objectCorners(1,1) = 0;
        objectCorners(1,2) = 0;

        objectCorners(2,1) = size(object,2);
        objectCorners(2,2) = 0;

        objectCorners(3,1) = size(object,2);
        objectCorners(3,2) = size(object,1);

        objectCorners(4,1) = 0;
        objectCorners(4,2) = size(object,1);

        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

        sceneCorners= cv.perspectiveTransform(objectCorners,H);//This is where the problem occurs

       %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

        imshow(im_matches);
        % Terminate if any user input
        flag = getappdata(window,'flag');
        if isempty(flag)||flag, break; end
        pause(0.000000001);
    end

% Close

    close(window);

end

The error:

Error using cv.perspectiveTransform
Unexpected Standard exception from MEX file.
What()
is:C:\slave\builds\WinInstallerMegaPack\src\opencv\modules\core\src\matmul.cpp:1926:
error: (-215) scn + 1 == m.cols && (depth == CV_32F || depth == CV_64F)

..

Error in hello (line 148)
     cv.perspectiveTransform(objectCorners,H);

Now , I have came across this which replicates my error . The problem faced in this post is similar to mine , and I fixed the issue regarding setting of object coordinates . How did I did that?. I have a working code which takes in live feed from webcam and matches images by checking out for homography in pure OpenCV ie without Matlab platform involved. The problem starts from checking out the perspectiveTranform(objCorners, H). Now , there is some ... (more)