2020-10-23 14:42:47 -0500 received badge ● Good Question (source) 2020-09-26 07:19:16 -0500 received badge ● Nice Question (source) 2020-05-05 15:43:10 -0500 received badge ● Popular Question (source) 2019-11-24 23:22:50 -0500 received badge ● Famous Question (source) 2019-11-06 07:27:15 -0500 received badge ● Famous Question (source) 2019-08-06 03:56:41 -0500 received badge ● Notable Question (source) 2019-07-25 03:37:34 -0500 received badge ● Famous Question (source) 2019-04-21 22:37:51 -0500 received badge ● Popular Question (source) 2018-12-18 04:30:15 -0500 received badge ● Notable Question (source) 2018-12-02 17:07:32 -0500 received badge ● Notable Question (source) 2018-10-28 19:20:17 -0500 received badge ● Popular Question (source) 2018-10-13 10:16:20 -0500 marked best answer Wait for a mouse click? I have a video. I would like to show the next frame only if the user clicks on a pixel on the current frame. (The user must select a point in each frame) Without using waitKey(0) I could I make opencv waiting for the mouse click before showing the next frame? 2018-09-22 17:12:09 -0500 received badge ● Good Answer (source) 2018-08-30 10:55:52 -0500 marked best answer check ransac outlier before perspectiveTransform ? Hello guys, I would like to draw outliers found by ransac with the classic method: H = findHomography( obj, scene, CV_RANSAC );  I saw in a snippet one can do something like: Mat points1t; perspectiveTransform(Mat(points1), points1t, H12); for( size_t i1 = 0; i1 < points1.size(); i1++ ) { if( norm(points2[i1] - points1t.at((int)i1,0)) <= maxInlierDist ) // inlier matchesMask[i1] = 1; }  But I don't understand why we need to call perspectiveTransform to find out which are the outlier if the outlier themself are calculted with the precedent istruction (findHomography) ? 2018-08-30 10:55:52 -0500 received badge ● Nice Answer (source) 2018-07-13 09:01:20 -0500 received badge ● Nice Question (source) 2018-07-12 14:40:37 -0500 received badge ● Notable Question (source) 2018-05-01 15:54:36 -0500 received badge ● Notable Question (source) 2018-03-05 04:19:37 -0500 received badge ● Famous Question (source) 2018-01-23 16:55:05 -0500 marked best answer How to know if two Mat point to the same data? I have two Mat a,b;  Eventually in the code it could happen a = b;  Is there any way to check whenever a and b points to the same data pointer (within code)? (Without drawing stuff on one image and showing the other) 2017-11-29 17:55:56 -0500 marked best answer Check if homography is good Basically I a am using a function bool niceHomography(const CvMat * H) { const double det = cvmGet(H, 0, 0) * cvmGet(H, 1, 1) - cvmGet(H, 1, 0) * cvmGet(H, 0, 1); if (det < 0) return false; const double N1 = sqrt(cvmGet(H, 0, 0) * cvmGet(H, 0, 0) + cvmGet(H, 1, 0) * cvmGet(H, 1, 0)); if (N1 > 4 || N1 < 0.1) return false; const double N2 = sqrt(cvmGet(H, 0, 1) * cvmGet(H, 0, 1) + cvmGet(H, 1, 1) * cvmGet(H, 1, 1)); if (N2 > 4 || N2 < 0.1) return false; const double N3 = sqrt(cvmGet(H, 2, 0) * cvmGet(H, 2, 0) + cvmGet(H, 2, 1) * cvmGet(H, 2, 1)); if (N3 > 0.002) return false; return true; }  to check whatever the homography is good or not (I have taken it from BRIEF_demo). Can anyone explain why we check the determinant like that, is there any theory behind it? To understand what I am talking about, that function avoids homography like this: Thanks 2017-09-07 07:37:15 -0500 received badge ● Popular Question (source) 2017-08-30 07:39:41 -0500 received badge ● Popular Question (source) 2017-08-07 08:53:36 -0500 received badge ● Famous Question (source) 2017-07-31 07:09:40 -0500 marked best answer Make a collage with other images I have a vector with images with different size. Then I have a bigger image (let's say 640x480) I want to make a grid collage like this: With variable numbers of cols. How would you do that? 2017-07-19 08:09:12 -0500 marked best answer matchShapes() example Hello Guys, I would like to use matchShapes() function for finding an object inside a query image. Let's say I have a model image of a book, i want to extract its shape and then try to find this book (its shape) inside another image. I have googled a lot but couldn't find any real example on how to use matchShapes to achive this. The documentation lacks. Can someoen make a little example in C++ ? Thanks a lot! (Note I know I can use SIFT/ORB etc, but i want to use matchShapes()) 2017-06-08 04:10:41 -0500 received badge ● Famous Question (source) 2017-06-01 22:46:30 -0500 received badge ● Famous Question (source) 2017-05-31 02:50:28 -0500 received badge ● Notable Question (source) 2017-04-25 15:41:57 -0500 received badge ● Popular Question (source) 2017-03-21 09:37:29 -0500 received badge ● Famous Question (source) 2017-01-13 13:47:07 -0500 received badge ● Famous Question (source) 2016-11-23 04:09:01 -0500 marked best answer calcOpticalFlowPyrLK doesn't respect window size? [bug ?] I am trying to use optical flow with opencv 2.4.5: calcOpticalFlowPyrLK() I am using similar parameters to the demo of the opencv:  Size winSize(6,6); // Small window size calcOpticalFlowPyrLK( prevFrame, currentFrame, points[0], points[1], status, err, winSize, 0, termcrit, 0, 0.001 // Only the input image );  But as you can see I have set the maxLevels to 0 (so it will process only the current layer). The problem is that this function sometimes returns a distance between points of over 100, if I do: for(int i=0;i features; vector locations; HOGDescriptor *hog = new HOGDescriptor(); hog->compute(image,featjres,Size(8,8), Size(32,32),locations);  Now I would like to use this information to find a match in a query image containg the object, I don't want to use SVM. Any sample code? And if the SVM is the only way, how can I train it with my model image? (Sample code if you can thanks) I wonder why it is not possibile to match it like we were matching SIFT descriptor and then doing a sort of ratio test =/ The SVM classifier needs training and it time consuming 2016-05-26 06:48:57 -0500 received badge ● Notable Question (source) 2016-05-13 02:46:40 -0500 received badge ● Popular Question (source) 2016-04-23 22:51:16 -0500 marked best answer Recovering images from motion blur knowing speed ? Hello guys, Let's say I have an Image took while the camera was moving (or the object was moving). Example: I know the direction and the length of the movement (for this example direction is 0° and length is ~15 pixel) Which way do you suggest me to correct this image? Thanks 2016-03-22 11:15:43 -0500 received badge ● Taxonomist