Why is this mistake?

Hi everyone, i'm working on visiontracekingfaceKLT. I'm tryng to run this code:

faceDetector = vision.CascadeObjectDetector();

videoFileReader = vision.VideoFileReader('tilted_face.avi');

videoFrame = step(videoFileReader); bbox = step(faceDetector, videoFrame);

x = bbox(1); y = bbox(2); w = bbox(3); h = bbox(4); bboxPolygon = [x, y, x+w, y, x+w, y+h, x, y+h];

shapeInserter = vision.ShapeInserter('Shape', 'Polygons', 'BorderColor','Custom',... 'CustomBorderColor',[255 255 0]); videoFrame = step(shapeInserter, videoFrame, bboxPolygon); figure; imshow(videoFrame); title('Detected face');

points = double(points); points(:, 1) = points(:, 1) + double(bbox(1)); points(:, 2) = points(:, 2) + double(bbox(2));

markerInserter = vision.MarkerInserter('Shape', 'Plus', ... 'BorderColor', 'White'); videoFrame = step(markerInserter, videoFrame, points); figure, imshow(videoFrame), title('Detected features');

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

initialize(pointTracker, double(points), rgb2gray(videoFrame));

videoInfo = info(videoFileReader); videoPlayer = vision.VideoPlayer('Position',... [100 100 videoInfo.VideoSize(1:2)+30]);

geometricTransformEstimator = vision.GeometricTransformEstimator(... 'PixelDistanceThreshold', 4, 'Transform', 'Nonreflective similarity');

oldPoints = double(points);

while ~isDone(videoFileReader)

    videoFrame = step(videoFileReader);

    [points, isFound] = step(pointTracker, rgb2gray(videoFrame));
    visiblePoints = points(isFound, :);
    oldInliers = oldPoints(isFound, :);

    if ~isempty(visiblePoints)
        [xform, geometricInlierIdx] = step(geometricTransformEstimator, ...
            double(oldInliers), double(visiblePoints));

        visiblePoints = visiblePoints(geometricInlierIdx, :);
        oldInliers = oldInliers(geometricInlierIdx, :);

        boxPoints = [reshape(bboxPolygon, 2, 4)', ones(4, 1)];
        boxPoints = boxPoints * xform;
        bboxPolygon = reshape(boxPoints', 1, numel(boxPoints));

        videoFrame = step(shapeInserter, videoFrame, bboxPolygon);

        videoFrame = step(markerInserter, videoFrame, visiblePoints);

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

    step(videoPlayer, videoFrame);
end

release(videoFileReader); release(videoPlayer); release(geometricTransformEstimator); release(pointTracker); close all

But it doesn't run, it appears: Attempted to access bbox(1); index out of bounds because numel(bbox)=0.

Error in visionfacetrackingKLT (line 9) x = bbox(1); y = bbox(2); w = bbox(3); h = bbox(4);

So if someone can help me to repair this mistake please do it. I will appreciate that a lot.

[Jan]

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Answer 1

[dpb]

aceDetector = vision.CascadeObjectDetector();
videoFileReader = vision.VideoFileReader('tilted_face.avi');
videoFrame = step(videoFileReader); 
bbox = step(faceDetector, videoFrame);
x = bbox(1); 
y = bbox(2);
w = bbox(3); 
h = bbox(4);
...

Attempted to access bbox(1); index out of bounds because numel(bbox)=0.
Error in visionfacetrackingKLT (line 9) x = bbox(1); y = bbox(2); w = bbox(3); h = bbox(4);

Well, there's no indication of what step is supposed to be but it ends up returning [] for bbox

Hence, since there are no elements in the array, referencing any is an error.

Your mission, should you choose to accept it, is to determine why that is so...or at least provide enough relevant information that someone here can have a clue, perhaps.

Answer 2

[Dima Lisin]

It looks like the face detector is not finding any faces in the first frame. You need to account for that in your code. Check bbox is empty, and if so, go to the next frame.