initialize

Initialize video frame and points to track

Syntax

initialize(pointTracker,points,I)

Description

initialize(pointTracker,points,I) initializes points to track and sets the initial video frame. The function sets the M-by-2 points array of [x y] coordinates with the points to track, and sets the initial video frame, I.

If you want to use the point tracker as a persistent variable, you must call initialize only during creation. If you call initialize in a loop, the previous state is lost and therefore, the tracker cannot maintain tracking.

Examples

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Track a Face in Scene

Open Script

Create System objects for reading and displaying video and for drawing a bounding box of the object.

videoReader = VideoReader('visionface.avi');
videoPlayer = vision.VideoPlayer('Position',[100,100,680,520]);

Read the first video frame, which contains the object, define the region.

objectFrame = readFrame(videoReader);
objectRegion = [264,122,93,93];

As an alternative, you can use the following commands to select the object region using a mouse. The object must occupy the majority of the region:

figure; imshow(objectFrame);

objectRegion=round(getPosition(imrect))

Show initial frame with a red bounding box.

objectImage = insertShape(objectFrame,'rectangle',objectRegion,'ShapeColor','red');
figure;
imshow(objectImage);
title('Red box shows object region');

Detect interest points in the object region.

points = detectMinEigenFeatures(im2gray(objectFrame),'ROI',objectRegion);

Display the detected points.

pointImage = insertMarker(objectFrame,points.Location,'+','MarkerColor','white');
figure;
imshow(pointImage);
title('Detected interest points');

Create a tracker object.

tracker = vision.PointTracker('MaxBidirectionalError',1);

Initialize the tracker.

initialize(tracker,points.Location,objectFrame);

Read, track, display points, and results in each video frame.

while hasFrame(videoReader)
      frame = readFrame(videoReader);
      [points,validity] = tracker(frame);
      out = insertMarker(frame,points(validity, :),'+');
      videoPlayer(out);
end