"conversion from ‘IplImage* {aka _IplImage*}’ to non-scalar type ‘cv::Mat’ requested" error when using cvQueryFrame

Question

I am trying to run the following code:

#include <highgui.h>
#include <iostream>
#include <stdio.h>
#include <cv.h>

using namespace std;
using namespace cv;
using namespace std;

int main()
{
    cvNamedWindow("Brezel detecting camera", 1);
    // Capture images from any camera connected to the system
    CvCapture* capture = cvCaptureFromCAM(CV_CAP_ANY);

    // Load the trained model
    CascadeClassifier brezelDetector;
    brezelDetector.load("src/person.xml");

    if (brezelDetector.empty())
    {
        printf("Empty model.");
        return 0;
    }

    char key;
    while (true)
    {
        // Get a frame from the camera
        Mat frame = cvQueryFrame(capture); //----->>>>>>> This line

        std::vector<Rect> brezels;

        // Detect brezels
        brezelDetector.detectMultiScale(frame, brezels, 1.1, 30,
                0 | CV_HAAR_SCALE_IMAGE, Size(200, 320));

        for (int i = 0; i < (int) brezels.size(); i++)
        {
            Point pt1(brezels[i].x, brezels[i].y);
            Point pt2(brezels[i].x + brezels[i].width,
                    brezels[i].y + brezels[i].width);

            // Draw a rectangle around the detected brezel
            rectangle(frame, pt1, pt2, Scalar(0, 0, 255), 2);
            putText(frame, "Brezel", pt1, FONT_HERSHEY_PLAIN, 1.0,
                    Scalar(255, 0, 0), 2.0);

        }

        // Show the transformed frame
        imshow("Brezel detecting camera", frame);

        // Read keystrokes, exit after ESC pressed
        key = cvWaitKey(10);
        if (char(key) == 27)
        {
            break;
        }
    }

    return 0;
}

But I am getting "conversion from ‘IplImage* {aka _IplImage*}’ to non-scalar type ‘cv::Mat’ requested" error on this line:

Mat frame = cvQueryFrame(capture);

I am using opencv3. How can I fix this issue?

Thanks,

Not sure but : `Mat` type is only for C++ Opencv and `cvQueryFrame` is used with C OpenCV, so you should choose one of those possibility : everything in C or everything in C++ — Pierre, Jan 26 '16 at 10:46
using a `VideoCapture` object (example at the end) : http://docs.opencv.org/2.4/modules/highgui/doc/reading_and_writing_images_and_video.html — Pierre, Jan 26 '16 at 10:49
please **avoid** using IplImage* and cv* functions at all cost. opencv moved away from that half a decade ago, you **must** use the c++ api (cv::Mat) consistently now. — berak, Jan 29 '16 at 12:43

score 4 · Accepted Answer · answered Jan 26 '16 at 11:31

4

Well, I don't really advise to you to use the old/obsolete IplImage format, but the conversion into cv::Mat is possible as below:

cv::Ptr<IplImage> iplimg(cvQueryFrame(capture)); // cv::Ptr<T> is safe ref-counting pointer class
if(!iplimg)
{
    break;
}

// cv::Mat replaces the CvMat and IplImage, but it's easy to convert
// between the old and the new data structures (by default, only the header
// is converted, while the data is shared)
cv::Mat img = cv::cvarrToMat(iplimg);

Why don't you use cv::VideoCapture instead?

cv::VideoCapture cap(0); // open the default camera
if(!cap.isOpened())  // check if we succeeded
    return -1;

while(true)
{
    cv::Mat frame;
    cap >> frame; // get a new frame from camera

    cv::imshow("frame", frame);
    cv::waitKey(1);
}

answered Jan 26 '16 at 11:31

Kornel

5,264
2
21
28

Thank you for your answer Kornel. But I am encountering a makefile error: /usr/local/lib/libopencv_imgproc.so.3.1: error adding symbols: DSO missing from command line – yusuf Jan 26 '16 at 12:10
1

this is a linker error, see the following for more information: http://stackoverflow.com/questions/19901934/strange-linking-error-dso-missing-from-command-line – Kornel Jan 26 '16 at 12:12
Kornel, actually this opencv3 is a headache. Is it logical to install opencv older versions? – yusuf Jan 26 '16 at 12:13
1

yes, why not? OpenCV 2.4.x is quite stable and provides a lot of functionality. I also have and maintain a lot of projects where we're using 2.4.x – Kornel Jan 26 '16 at 12:18

Siim Veskilt · Answer 2 · 2016-01-26T11:05:46.493

1

Try using the constructor:

Mat frame(cvQueryFrame(capture));

Or with newer OpenCV versions where the constructor has been removed:

Mat frame = cvarrToMat(cvQueryFrame(capture));

edited Jan 26 '16 at 11:05

answered Jan 26 '16 at 10:55

Siim Veskilt

80
10

Sorry, but it gives this error: no matching function for call to ‘cv::Mat::Mat(IplImage*)’ – yusuf Jan 26 '16 at 11:00
1

Oh, they must have changed it in newer versions... try converting with the cv::cvarrToMat function instead. – Siim Veskilt Jan 26 '16 at 11:04
Now I get this error: undefined reference to `cv::cvarrToMat(void const*, bool, bool, int, cv::AutoBuffer*)' – yusuf Jan 26 '16 at 11:09
1

This is a linking error so please post your link line. – Siim Veskilt Jan 26 '16 at 11:15
What do you mean by link line? – yusuf Jan 26 '16 at 11:15
#include #include #include #include using namespace std; using namespace cv; using namespace std; – yusuf Jan 26 '16 at 11:16
1

The commands that the linker uses, it looks something like g++ -o file file.cpp `pkg-config opencv --cflags --libs` – Siim Veskilt Jan 26 '16 at 11:16
I'm running it under eclipse. – yusuf Jan 26 '16 at 11:17
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/101667/discussion-between-siim-veskilt-and-yusuf). – Siim Veskilt Jan 26 '16 at 11:17
Well. it is weird. I have managed to run the same code before. After formatting my computer, I have installed the latest version of opencv again, and I have started to get weird errors. – yusuf Jan 26 '16 at 11:18

score 0 · Answer 3 · answered Jan 29 '16 at 08:18

0

First get image in IplImage like this:

IplImage* image = cvQueryFrame(capture);

then,

Mat matImage(image);

answered Jan 29 '16 at 08:18

Sagar Patel

864
1
11
22

"conversion from ‘IplImage* {aka _IplImage*}’ to non-scalar type ‘cv::Mat’ requested" error when using cvQueryFrame

3 Answers3