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POWhy cvFindContours() method doesn't detect Contours correctly in javacv?
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  1. POWhy cvFindContours() method doesn't detect Contours correctly in javacv?
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    copied!<p>I went through many questions in StackOverflow and able to develop small program to detect squares and rectangles correctly. This is my sample code</p> <pre><code>public static CvSeq findSquares(final IplImage src, CvMemStorage storage) { CvSeq squares = new CvContour(); squares = cvCreateSeq(0, sizeof(CvContour.class), sizeof(CvSeq.class), storage); IplImage pyr = null, timg = null, gray = null, tgray; timg = cvCloneImage(src); CvSize sz = cvSize(src.width(), src.height()); tgray = cvCreateImage(sz, src.depth(), 1); gray = cvCreateImage(sz, src.depth(), 1); // cvCvtColor(gray, src, 1); pyr = cvCreateImage(cvSize(sz.width() / 2, sz.height() / 2), src.depth(), src.nChannels()); // down-scale and upscale the image to filter out the noise // cvPyrDown(timg, pyr, CV_GAUSSIAN_5x5); // cvPyrUp(pyr, timg, CV_GAUSSIAN_5x5); // cvSaveImage("ha.jpg",timg); CvSeq contours = new CvContour(); // request closing of the application when the image window is closed // show image on window // find squares in every color plane of the image for (int c = 0; c &lt; 3; c++) { IplImage channels[] = { cvCreateImage(sz, 8, 1), cvCreateImage(sz, 8, 1), cvCreateImage(sz, 8, 1) }; channels[c] = cvCreateImage(sz, 8, 1); if (src.nChannels() &gt; 1) { cvSplit(timg, channels[0], channels[1], channels[2], null); } else { tgray = cvCloneImage(timg); } tgray = channels[c]; // // try several threshold levels for (int l = 0; l &lt; N; l++) { // hack: use Canny instead of zero threshold level. // Canny helps to catch squares with gradient shading if (l == 0) { // apply Canny. Take the upper threshold from slider // and set the lower to 0 (which forces edges merging) cvCanny(tgray, gray, 0, thresh, 5); // dilate canny output to remove potential // // holes between edge segments cvDilate(gray, gray, null, 1); } else { // apply threshold if l!=0: cvThreshold(tgray, gray, (l + 1) * 255 / N, 255, CV_THRESH_BINARY); } // find contours and store them all as a list cvFindContours(gray, storage, contours, sizeof(CvContour.class), CV_RETR_LIST, CV_CHAIN_APPROX_SIMPLE); CvSeq approx; // test each contour while (contours != null &amp;&amp; !contours.isNull()) { if (contours.elem_size() &gt; 0) { approx = cvApproxPoly(contours, Loader.sizeof(CvContour.class), storage, CV_POLY_APPROX_DP, cvContourPerimeter(contours) * 0.02, 0); if (approx.total() == 4 &amp;&amp; Math.abs(cvContourArea(approx, CV_WHOLE_SEQ, 0)) &gt; 1000 &amp;&amp; cvCheckContourConvexity(approx) != 0) { double maxCosine = 0; for (int j = 2; j &lt; 5; j++) { // find the maximum cosine of the angle between // joint edges double cosine = Math.abs(angle( new CvPoint(cvGetSeqElem( approx, j % 4)), new CvPoint(cvGetSeqElem( approx, j - 2)), new CvPoint(cvGetSeqElem( approx, j - 1)))); maxCosine = Math.max(maxCosine, cosine); } if (maxCosine &lt; 0.2) { CvRect x = cvBoundingRect(approx, l); if ((x.width() * x.height()) &lt; 50000) { System.out.println("Width : " + x.width() + " Height : " + x.height()); cvSeqPush(squares, approx); } } } } contours = contours.h_next(); } contours = new CvContour(); } } return squares; } </code></pre> <p>I use this image to detect rectangles and squares</p> <p><img src="https://i.stack.imgur.com/cZ2Ka.jpg" alt="enter image description here"></p> <p>I need to identify the following output</p> <p><img src="https://i.stack.imgur.com/uiDtZ.jpg" alt="enter image description here"></p> <p>and</p> <p><img src="https://i.stack.imgur.com/MAHmR.jpg" alt="enter image description here"></p> <p>But when I run the above code, it detects only the following rectangles. But I don't know the reason for that. Please can someone explain the reason for that.</p> <p>This is the output that I got.</p> <p><img src="https://i.stack.imgur.com/jaUsX.png" alt="enter image description here"></p> <p>Please be kind enough to explain the problem in above code and give some suggensions to detect this squares and rectangles.</p>
 

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