opencv 3.0中的错误标志错误

Question

I am relatively new to opencv and C++ and I would like some help on my code. For my project, I am currently working on a simple blob detector but when I run it, I get "OpenCV Error: Bad flag (parameter or structure field) (Unrecognized or unsupported array type) in cvGetMat, file C:\\builds\\master_PackSlave-win64-vc12-shared\\opencv\\modules\\core\\src\\array.cpp, line 2494 Press any key to continue . . ." . I am pretty sure that the error is either from the Mat im_with_keypoints;, or a problem in linker. Below is my code. If you could help me that would be great.

• Update: I ran this program through the debugger and came out with this error
  • I am also using visual studio 2015

This is the image I am trying to detect for blobs:

#include "opencv2/highgui/highgui.hpp"  
#include "opencv2/features2d.hpp"
#include "opencv2/opencv.hpp"
#include <opencv2/core/core.hpp>

using namespace cv;
using namespace std;

int main(int argc, char** argv)
{


    Mat im = imread("Eagle_coins.jpg", IMREAD_GRAYSCALE);


    SimpleBlobDetector::Params params;

    params.minThreshold = 10;
    params.maxThreshold = 200;

    params.filterByColor = true;

    params.filterByCircularity = true;
    params.minCircularity = 0.1;
    params.maxCircularity = 0.28;


    params.filterByConvexity = true;
    params.minConvexity = 0.87;
    params.maxConvexity = 2.8;


    params.filterByInertia = true;
    params.minInertiaRatio = 0.01;
    params.maxInertiaRatio = 2;

    vector<KeyPoint> keypoints;

    Ptr<SimpleBlobDetector> detector = SimpleBlobDetector::create(params);

    detector->detect(im, keypoints);

    Mat im_with_keypoints;
    drawKeypoints(im, keypoints, im_with_keypoints, Scalar(0, 0, 255),                       DrawMatchesFlags::DRAW_RICH_KEYPOINTS);

    imshow("white", im_with_keypoints);
    waitKey(0);

}

Answer 1

The minimal code that reproduces the error you mention looks as follows:

#include <opencv2/opencv.hpp>
#include <opencv2/features2d.hpp>
#include <opencv2/highgui/highgui.hpp>

int main(int argc, char** argv)
{
    cv::Mat im;

    cv::SimpleBlobDetector::Params params;
    std::vector<cv::KeyPoint> keypoints;
    cv::Ptr<cv::SimpleBlobDetector> detector = cv::SimpleBlobDetector::create(params);
    detector->detect(im, keypoints);
}

Console contains

OpenCV Error: Bad flag (parameter or structure field) (Unrecognized or unsupported array type) in cvGetMat, file C:\\builds\\master_PackSlave-win64-vc12-shared\\opencv\\modules\\core\\src\\array.cpp, line 2494

and I get a exception from detector->detect with with the message

Unhandled exception at 0x00007FF9A88C7788 in so03.exe: Microsoft C++ exception: cv::Exception at memory location 0x0000005BA676E230.

Sidenote: The source of the error would be much more obvious in the debugger, if you had the debug symbols (PDB) available for the library. Unfortunately the package with precompiled binaries distributed from the OpenCV site doesn't contain those, which is why I prefer to build my own.

It goes away when we pass a non-empty cv::Mat to detect :

#include <opencv2/opencv.hpp>
#include <opencv2/features2d.hpp>
#include <opencv2/highgui/highgui.hpp>

int main(int argc, char** argv)
{
    cv::Mat im(100, 100, CV_8UC3);

    cv::SimpleBlobDetector::Params params;
    std::vector<cv::KeyPoint> keypoints;
    cv::Ptr<cv::SimpleBlobDetector> detector = cv::SimpleBlobDetector::create(params);
    detector->detect(im, keypoints);
}

From this we can conclude, that in your example, imread fails to load the image. This is entirely possible, since you don't check for this situation.

Add something like this right after your call to imread :

if (im.empty()) {
    std::cerr << "Failed to load image.\n";
    return -1;
}

Now, as to why the image is not loading correctly. One option, since you're using Visual Studio, is that you don't have your working directory set up correctly -- by default this is where the project file is located, which is probably not where the exe is. Either set Debugging > Working Directory appropriately in your project's properties, or use an absolute path to load the image.