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2020-11-19 02:15:59 -0500 asked a question Use build_sdk.py to build opencv4 for android on Windows

Use build_sdk.py to build opencv4 for android on Windows Hi, I need to build OpenCV for Android on Windows10. The OpenCV

2020-09-26 21:44:46 -0500 asked a question Use build_sdk.py to build OpenCV for Android

Use build_sdk.py to build OpenCV for Android Hi, I use command: D:\build-android> python opencv-master\platforms\andr

2020-09-22 04:41:17 -0500 asked a question how to get a outputarrayofarrays

how to get a outputarrayofarrays Hi, I have a method func(OutputArrayOfArrays points) { vector < vector < Point

2020-09-21 02:58:11 -0500 commented question build opencv with java wrapper for android

It works. Thanks!

2020-09-19 02:56:52 -0500 commented question build opencv with java wrapper for android

My question is how to build OpenCV with java wrapper for android rather than how to use a prebuild OpenCV-android.

2020-09-18 07:05:01 -0500 asked a question build opencv with java wrapper for android

build opencv with java wrapper for android Hi, I added some functionality in the chessboard.cpp and I can compile it on

2020-09-16 20:56:40 -0500 commented answer build OpenCV4: add preprocessor definition "CV_DETECTORS_CHESSBOARD_DEBUG"

yes, I can add include path for highgui, but which dependents on other include files which depend on others...

2020-09-16 05:29:38 -0500 commented answer build OpenCV4: add preprocessor definition "CV_DETECTORS_CHESSBOARD_DEBUG"

I uncommeted it in chessboard.cpp and get the error: cannot open source file "opencv2/highgui.hpp"

2020-09-16 02:38:15 -0500 asked a question build OpenCV4: add preprocessor definition "CV_DETECTORS_CHESSBOARD_DEBUG"

build OpenCV4: add preprocessor definition "CV_DETECTORS_CHESSBOARD_DEBUG" Hi, I am building OpenCV4 on Windows using VS

2020-08-04 06:53:03 -0500 commented question white angle and black angle in chessboard

Actually I know where is the source code. I want to know the reference the algorithm is based on.

2020-08-04 03:30:58 -0500 commented question white angle and black angle in chessboard

I am using OpenCV4.4. cv::details::Chessboard::Board.

2020-08-04 02:04:20 -0500 asked a question white angle and black angle in chessboard

white angle and black angle in chessboard Hi, I am reading the source code about two classes: Chessboard and Chessboard:

2020-07-09 20:17:08 -0500 commented question Nonlinear solver such as Levenberg- Marquardt

Thank you so much!

2020-07-08 04:43:24 -0500 asked a question Nonlinear solver such as Levenberg- Marquardt

Nonlinear solver such as Levenberg- Marquardt Hi, I need to use a nonlinear solver in OpenCV. Does OpenCV support it or

2020-05-17 22:38:58 -0500 commented question Find rigid 3D transform between two 3D point sets

ICP does not require the correspondence. Since I already know the correspondence, maybe some more efficient methods exi

2020-05-16 23:28:20 -0500 asked a question Find rigid 3D transform between two 3D point sets

Find rigid 3D transform between two 3D point sets Hi, I have two 3D point sets with known correspondence and I want to f

2020-01-08 19:34:19 -0500 commented question Jitter using ArUco marker

Thanks. The noisy measurement you mean is the rotation and translation vector estimated by estimatePoseSingleMarkers, ri

2020-01-08 05:35:00 -0500 asked a question Jitter using ArUco marker

Jitter using ArUco marker Hi, I am using ArUco marker to find the pose. The dictionary is DICT_6X6_250 and the physical

2020-01-05 03:36:38 -0500 asked a question combine six ArUco markers into a cuboid marker

combine six ArUco markers into a cuboid marker Hi, I want to use six ArUco markers and each one is attached on one side

2020-01-02 05:34:24 -0500 commented question Pose estimation of a small cube shape marker

Actually, I want to know the underlying technique to do the pose estimation of a cubic marker. It is better if people ca

2020-01-02 04:21:05 -0500 asked a question Pose estimation of a small cube shape marker

Pose estimation of a small cube shape marker Hi, I would like to estimate the pose of a needle, looks like a thin cylind

2019-12-12 20:41:14 -0500 commented question Jitter problem of the pose estimated by SolvePnp

Thanks a lot. I will try it.

2019-12-12 07:17:48 -0500 received badge  Student (source)
2019-12-12 07:04:02 -0500 asked a question Jitter problem of the pose estimated by SolvePnp

Jitter problem of the pose estimated by SolvePnp Hi, I use SolvePnp to estimate the pose of the head. The 2D points come

2019-12-12 02:45:44 -0500 asked a question Pose estimation of a needle

Pose estimation of a needle Hi, I would like to real-time to estimate the pose of a needle hold by the hand. The needle

2019-11-21 19:49:55 -0500 commented question App crash when using solvePnP on Android

Thanks. I need at leas 6 points rather than 4.

2019-11-20 06:47:19 -0500 asked a question App crash when using solvePnP on Android

App crash when using solvePnP on Android Hi, I use OpenCV on Andoid. I can use it for face detection. But when I use it

2019-10-16 07:07:47 -0500 marked best answer sync failed when adding opencv as a dependence for my app

Hi, I want to use opencv-4.1.1-android-sdk in my app. My android studio version is 3.3.2 and sdk api is 28. I use Windows. I copied all libs under native/libs to my jniLibs folder. Then I import new module by specify the sdk/java folder and it succeed. However, when I open module setting and add dependence, I got sync error as following:

ERROR: Unable to resolve dependency for ':app@debug/compileClasspath': Could not resolve project :opencvjavasupport. Show Details Affected Modules: app

Any help are very appreciated.

Thanks.

YL

2019-10-16 07:07:40 -0500 commented answer sync failed when adding opencv as a dependence for my app

It works. Many thanks.

2019-10-13 23:13:51 -0500 asked a question sync failed when adding opencv as a dependence for my app

sync failed when adding opencv as a dependence for my app Hi, I want to use opencv-4.1.1-android-sdk in my app. My andro

2018-06-08 11:00:15 -0500 received badge  Enthusiast
2018-06-07 20:40:40 -0500 asked a question Camera calibration with fixed principal point

Camera calibration with fixed principal point Hi, I would like to use cv::calibrateCamera to do camera calibration. In m

2018-05-25 19:13:29 -0500 asked a question Is it sufficient just using one image to calibrate a camera with good initialization known?

Is it sufficient just using one image to calibrate a camera with good initialization known? Hi, I have a question for ca

2018-05-25 19:13:27 -0500 asked a question Is it sufficient just using one image to calibrate a camera with good initialization known?

Is it sufficient just using one image to calibrate a camera with good initialization known? Hi, I have a question for ca

2018-03-20 11:49:13 -0500 received badge  Supporter (source)
2018-03-20 11:49:08 -0500 received badge  Scholar (source)
2018-03-20 07:06:25 -0500 marked best answer Track ArUco marker in gray scale OpenCV image?

Hi, I want to use ArUco marker to do AR and I want to know if I can track the ArUco marker in a grays scale OpenCV image?

Thanks.

YL

2018-03-19 19:53:33 -0500 asked a question Track ArUco marker in gray scale OpenCV image?

Track ArUco marker in gray scale OpenCV image? Hi, I want to use ArUco marker to do AR and I want to know if I can trac

2017-06-16 18:16:09 -0500 asked a question bug in SimpleBlobDetector?

Hi, I am looking the implementation of SimpleBlobDetector. It looks the insertions sort is not correct as shown below. I also copy entire SimpleBlobDetector codes at the end.

For the insertion sort, we should compare with the key or switch values, right? The following OpenCV code looks weird.

size_t k = centers[j].size() - 1;
while( k > 0 && centers[j][k].radius < centers[j][k-1].radius )//compare with key
{
    centers[j][k] = centers[j][k-1];//or switch values here
    k--;
}
centers[j][k] = curCenters[i];

Entire blob detection codes:

void SimpleBlobDetectorImpl::detect(InputArray image, std::vector<cv::KeyPoint>& keypoints, InputArray)
{
    //TODO: support mask
    keypoints.clear();
    Mat grayscaleImage;
    if (image.channels() == 3)
        cvtColor(image, grayscaleImage, COLOR_BGR2GRAY);
    else
        grayscaleImage = image.getMat();

    std::vector < std::vector<Center> > centers;
    for (double thresh = params.minThreshold; thresh < params.maxThreshold; thresh += params.thresholdStep)
    {
        Mat binarizedImage;
        threshold(grayscaleImage, binarizedImage, thresh, 255, THRESH_BINARY);

        std::vector < Center > curCenters;
        findBlobs(grayscaleImage, binarizedImage, curCenters);
        std::vector < std::vector<Center> > newCenters;
        for (size_t i = 0; i < curCenters.size(); i++)
        {
            bool isNew = true;
            for (size_t j = 0; j < centers.size(); j++)
            {
                double dist = norm(centers[j][ centers[j].size() / 2 ].location - curCenters[i].location);
                isNew = dist >= params.minDistBetweenBlobs && dist >= centers[j][ centers[j].size() / 2 ].radius && dist >= curCenters[i].radius;
                if (!isNew)
                {
                    centers[j].push_back(curCenters[i]);

                    size_t k = centers[j].size() - 1;
                    while( k > 0 && centers[j][k].radius < centers[j][k-1].radius )
                    {
                        centers[j][k] = centers[j][k-1];//should switch here?
                        k--;
                    }
                    centers[j][k] = curCenters[i];

                    break;
                }
            }
            if (isNew)
                newCenters.push_back(std::vector<Center> (1, curCenters[i]));
        }
        std::copy(newCenters.begin(), newCenters.end(), std::back_inserter(centers));
    }

    for (size_t i = 0; i < centers.size(); i++)
    {
        if (centers[i].size() < params.minRepeatability)
            continue;
        Point2d sumPoint(0, 0);
        double normalizer = 0;
        for (size_t j = 0; j < centers[i].size(); j++)
        {
            sumPoint += centers[i][j].confidence * centers[i][j].location;
            normalizer += centers[i][j].confidence;
        }
        sumPoint *= (1. / normalizer);
        KeyPoint kpt(sumPoint, (float)(centers[i][centers[i].size() / 2].radius) * 2.0f);
        keypoints.push_back(kpt);
    }
}
2017-05-06 01:09:56 -0500 asked a question Which color space should I use to detect some color balls

Hi, I have NV12 (one of YUV) format video and I want to real-time detect some color balls with diameter around 10mm in the video. The ball will somehow change its color in the video due to the environment light and its reflection. I think the first step is to do the threshold. Which color space is suitable for the thresholding? RGB, YUV or HSV?

Many thanks.

YL

2017-04-15 19:29:47 -0500 commented question Pose tracking for an object with 4 spheres (markers)

Thanks. Would you please let me know how to do ellipse detection for a YUV format video?

2017-03-23 21:47:35 -0500 asked a question Pose tracking for an object with 4 spheres (markers)

Hi, I have an object with four sphere with coordinates (center of the sphere): A: 0.0, 0.0, 0.0 B: 0.0, 0.0, 50.0 C: 0.0, 25.0, 100.0 D: 0.0, -25.0, 135.0

There four spheres have diameter around 1 cm and have a gray color. The capture video has YUV format. To track the pose of the object, I think I need to first detect the center of the four spheres in the video. Any suggestion about a fast sphere detection?

After detect the spheres, I am not sure treating the object as a planar object and use SolvePNP to estimate pose or treating the object as a 3D object and use POSIT to estimate pose.

Thanks a lot.

YL