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doc/js_tutorials/js_video/js_meanshift/js_meanshift.markdown

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+Meanshift and Camshift {#tutorial_js_meanshift}
+======================
+
+Goal
+----
+
+-   We will learn about Meanshift and Camshift algorithms to find and track objects in videos.
+
+Meanshift
+---------
+
+The intuition behind the meanshift is simple. Consider you have a set of points. (It can be a pixel
+distribution like histogram backprojection). You are given a small window ( may be a circle) and you
+have to move that window to the area of maximum pixel density (or maximum number of points). It is
+illustrated in the simple image given below:
+
+![image](images/meanshift_basics.jpg)
+
+The initial window is shown in blue circle with the name "C1". Its original center is marked in blue
+rectangle, named "C1_o". But if you find the centroid of the points inside that window, you will
+get the point "C1_r" (marked in small blue circle) which is the real centroid of window. Surely
+they don't match. So move your window such that circle of the new window matches with previous
+centroid. Again find the new centroid. Most probably, it won't match. So move it again, and continue
+the iterations such that center of window and its centroid falls on the same location (or with a
+small desired error). So finally what you obtain is a window with maximum pixel distribution. It is
+marked with green circle, named "C2". As you can see in image, it has maximum number of points. The
+whole process is demonstrated on a static image below:
+
+![image](images/meanshift_face.gif)
+
+So we normally pass the histogram backprojected image and initial target location. When the object
+moves, obviously the movement is reflected in histogram backprojected image. As a result, meanshift
+algorithm moves our window to the new location with maximum density.
+
+### Meanshift in OpenCV.js
+
+To use meanshift in OpenCV.js, first we need to setup the target, find its histogram so that we can
+backproject the target on each frame for calculation of meanshift. We also need to provide initial
+location of window. For histogram, only Hue is considered here. Also, to avoid false values due to
+low light, low light values are discarded using **cv.inRange()** function.
+
+We use the function: **cv.meanShift (probImage, window, criteria)**
+@param probImage     Back projection of the object histogram. See cv.calcBackProject for details.
+@param window        Initial search window.
+@param criteria      Stop criteria for the iterative search algorithm.
+@return              number of iterations meanShift took to converge and the new location
+
+### Try it
+
+\htmlonly
+<iframe src="../../js_meanshift.html" width="100%"
+        onload="this.style.height=this.contentDocument.body.scrollHeight +'px';">
+</iframe>
+\endhtmlonly
+
+Camshift
+--------
+
+Did you closely watch the last result? There is a problem. Our window always has the same size when
+the object is farther away and it is very close to camera. That is not good. We need to adapt the window
+size with size and rotation of the target. Once again, the solution came from "OpenCV Labs" and it
+is called CAMshift (Continuously Adaptive Meanshift) published by Gary Bradsky in his paper
+"Computer Vision Face Tracking for Use in a Perceptual User Interface" in 1988.
+
+It applies meanshift first. Once meanshift converges, it updates the size of the window as,
+\f$s = 2 \times \sqrt{\frac{M_{00}}{256}}\f$. It also calculates the orientation of best fitting ellipse
+to it. Again it applies the meanshift with new scaled search window and previous window location.
+The process is continued until required accuracy is met.
+
+![image](images/camshift_face.gif)
+
+### Camshift in OpenCV.js
+
+It is almost same as meanshift, but it returns a rotated rectangle (that is our result) and box
+parameters (used to be passed as search window in next iteration).
+
+We use the function: **cv.CamShift (probImage, window, criteria)**
+@param probImage     Back projection of the object histogram. See cv.calcBackProject for details.
+@param window        Initial search window.
+@param criteria      Stop criteria for the iterative search algorithm.
+@return              Rotated rectangle and the new search window
+
+### Try it
+
+\htmlonly
+<iframe src="../../js_camshift.html" width="100%"
+        onload="this.style.height=this.contentDocument.body.scrollHeight +'px';">
+</iframe>
+\endhtmlonly
+
+Additional Resources
+--------------------
+
+-#  French Wikipedia page on [Camshift](http://fr.wikipedia.org/wiki/Camshift). (The two animations
+    are taken from here)
+2.  Bradski, G.R., "Real time face and object tracking as a component of a perceptual user
+    interface," Applications of Computer Vision, 1998. WACV '98. Proceedings., Fourth IEEE Workshop
+    on , vol., no., pp.214,219, 19-21 Oct 1998