I am trying to track face in a video using KLT in Matlab R2014b but I don't know how to remove this error "Expected ROI to be an array with number of elements equal to 4". Can any one help?

clc;

clear all;

faceDetector = vision.CascadeObjectDetector();

videoFileReader = vision.VideoFileReader('labedit.mp4');

videoFrame = step(videoFileReader);

bbox = step(faceDetector, videoFrame);

videoFrame = insertShape(videoFrame, 'Rectangle', bbox);

figure; imshow(videoFrame); title('Detected face');

bboxPoints = bbox2points(bbox(1, :)); disp(bboxPoints(1,1));

points = detectMinEigenFeatures(rgb2gray(videoFrame), 'ROI', bbox);

figure, imshow(videoFrame), hold on, title('Detected features'); plot(points);

pointTracker = vision.PointTracker('MaxBidirectionalError', 2);

points = points.Location; initialize(pointTracker, points, videoFrame);

videoPlayer = vision.VideoPlayer('Position',... [100 100 [size(videoFrame, 2), size(videoFrame, 1)]+30]);

oldPoints = points;

while ~isDone(videoFileReader)

    videoFrame = step(videoFileReader);

    [points, isFound] = step(pointTracker, videoFrame);
    visiblePoints = points(isFound, :);
    oldInliers = oldPoints(isFound, :);

    if size(visiblePoints, 1) >= 2 % need at least 2 points

        [xform, oldInliers, visiblePoints] = estimateGeometricTransform(...
            oldInliers, visiblePoints, 'similarity', 'MaxDistance', 4);

        bboxPoints = transformPointsForward(xform, bboxPoints);

        bboxPolygon = reshape(bboxPoints', 1, []);
        videoFrame = insertShape(videoFrame, 'Polygon', bboxPolygon, ...
            'LineWidth', 2);

        videoFrame = insertMarker(videoFrame, visiblePoints, '+', ...
            'Color', 'white');

        oldPoints = visiblePoints;
        setPoints(pointTracker, oldPoints);
    end

    step(videoPlayer, videoFrame);
end

% Clean up

release(videoFileReader);

release(videoPlayer);

release(pointTracker);

[Adil Mukhtar]

I got this error when this line executes points = detectMinEigenFeatures(rgb2gray(videoFrame), 'ROI', bbox);

Answer 1

[Dima Lisin]

Hi Adil,

It looks like the face detector did not detect anything. You have to check whether bbox is empty.

[Jean-Sébastien Herbaux]

Hello, I have the same error, but : for a video with only one face, it's working well and on the other case, with a multi-face video, the console is answering the following error

Error using detectMinEigenFeatures (line 58)
Expected ROI to be an array with number of elements equal to 4.

Error in face_tracking (line 17)
points = detectMinEigenFeatures(rgb2gray(videoFrame), 'ROI', bbox);

Any help ?

[Muhammad Irfan]

Any positive response from anyone Jean-Sébastien Herbaux? I have faced same error

[RENFIX]

You must resize image or video input and then run again