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POOpenCV 2.4.2 calcOpticalFlowPyrLK doesn't find any points
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  1. POOpenCV 2.4.2 calcOpticalFlowPyrLK doesn't find any points
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    copied!<p>I am using OpenCV 2.4.2 on Linux. I am writing in C++. I want to track simple objects (e.g. black rectangle on the white background). Firstly I am using goodFeaturesToTrack and then calcOpticalFlowPyrLK to find those points on another image. The problem is that calcOpticalFlowPyrLK doesn't find those points.</p> <p>I have found code that does it in C, which does not work in my case: <a href="http://dasl.mem.drexel.edu/~noahKuntz/openCVTut9.html" rel="nofollow">http://dasl.mem.drexel.edu/~noahKuntz/openCVTut9.html</a></p> <p>I have converted it into C++:</p> <pre><code>int main(int, char**) { Mat imgAgray = imread("ImageA.png", CV_LOAD_IMAGE_GRAYSCALE); Mat imgBgray = imread("ImageB.png", CV_LOAD_IMAGE_GRAYSCALE); Mat imgC = imread("ImageC.png", CV_LOAD_IMAGE_UNCHANGED); vector&lt;Point2f&gt; cornersA; goodFeaturesToTrack(imgAgray, cornersA, 30, 0.01, 30); for (unsigned int i = 0; i &lt; cornersA.size(); i++) { drawPixel(cornersA[i], &amp;imgC, 2, blue); } // I have no idea what does it do // cornerSubPix(imgAgray, cornersA, Size(15, 15), Size(-1, -1), // TermCriteria(TermCriteria::COUNT + TermCriteria::EPS, 20, 0.03)); vector&lt;Point2f&gt; cornersB; vector&lt;uchar&gt; status; vector&lt;float&gt; error; // winsize has to be 11 or 13, otherwise nothing is found int winsize = 11; int maxlvl = 5; calcOpticalFlowPyrLK(imgAgray, imgBgray, cornersA, cornersB, status, error, Size(winsize, winsize), maxlvl); for (unsigned int i = 0; i &lt; cornersB.size(); i++) { if (status[i] == 0 || error[i] &gt; 0) { drawPixel(cornersB[i], &amp;imgC, 2, red); continue; } drawPixel(cornersB[i], &amp;imgC, 2, green); line(imgC, cornersA[i], cornersB[i], Scalar(255, 0, 0)); } namedWindow("window", 1); moveWindow("window", 50, 50); imshow("window", imgC); cvWaitKey(0); return 0; } </code></pre> <blockquote> <p>ImageA: <a href="http://oi50.tinypic.com/14kv05v.jpg" rel="nofollow">http://oi50.tinypic.com/14kv05v.jpg</a></p> <p>ImageB: <a href="http://oi46.tinypic.com/4l3xom.jpg" rel="nofollow">http://oi46.tinypic.com/4l3xom.jpg</a></p> <p>ImageC: <a href="http://oi47.tinypic.com/35n3uox.jpg" rel="nofollow">http://oi47.tinypic.com/35n3uox.jpg</a></p> </blockquote> <p>I have found out that it works only for winsize = 11. I have tried using it on a moving rectangle to check how far it is from the origin. It hardly ever detects all four corners.</p> <pre><code>int main(int, char**) { std::cout &lt;&lt; "Compiled at " &lt;&lt; __TIME__ &lt;&lt; std::endl; Scalar white = Scalar(255, 255, 255); Scalar black = Scalar(0, 0, 0); Scalar red = Scalar(0, 0, 255); Rect rect = Rect(50, 100, 100, 150); Mat org = Mat(Size(640, 480), CV_8UC1, white); rectangle(org, rect, black, -1, 0, 0); vector&lt;Point2f&gt; features; goodFeaturesToTrack(org, features, 30, 0.01, 30); std::cout &lt;&lt; "POINTS FOUND:" &lt;&lt; std::endl; for (unsigned int i = 0; i &lt; features.size(); i++) { std::cout &lt;&lt; "Point found: " &lt;&lt; features[i].x; std::cout &lt;&lt; " " &lt;&lt; features[i].y &lt;&lt; std::endl; } bool goRight = 1; while (1) { if (goRight) { rect.x += 30; rect.y += 30; if (rect.x &gt;= 250) { goRight = 0; } } else { rect.x -= 30; rect.y -= 30; if (rect.x &lt;= 50) { goRight = 1; } } Mat frame = Mat(Size(640, 480), CV_8UC1, white); rectangle(frame, rect, black, -1, 0, 0); vector&lt;Point2f&gt; found; vector&lt;uchar&gt; status; vector&lt;float&gt; error; calcOpticalFlowPyrLK(org, frame, features, found, status, error, Size(11, 11), 5); Mat display; cvtColor(frame, display, CV_GRAY2BGR); for (unsigned int i = 0; i &lt; found.size(); i++) { if (status[i] == 0 || error[i] &gt; 0) { continue; } else { line(display, features[i], found[i], red); } } namedWindow("window", 1); moveWindow("window", 50, 50); imshow("window", display); if (cvWaitKey(300) &gt; 0) { break; } } } </code></pre> <p>OpenCV implementation of Lucas-Kanade seems to be unable to track a rectangle on a binary image. Am I doing something wrong or does this function just not work?</p>
 

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