How to fill Matrix with zeros in OpenCV?

Question

The code below causes an exception. Why?

#include <opencv2/core/core.hpp> #include <iostream>  using namespace cv; using namespace std;  void main() {      try {         Mat m1 = Mat(1,1, CV_64F, 0);         m1.at<double>(0,0) = 0;     }     catch(cv::Exception &e) {         cerr << e.what() << endl;     }  } 

Error is follows:

OpenCV Error: Assertion failed (dims <= 2 && data && (unsigned)i0 < (unsigned)size.p[0] && (unsigned)(i1*DataType<_Tp>::channels) < (unsigned)(size.p[1]*channels()) && ((((sizeof(size_t)<<28)|0x8442211) >> ((DataType<_Tp>::depth) & ((1 << 3 ) - 1))*4) & 15) == elemSize1()) in unknown function, file %OPENCV_DIR%\build\include\opencv2\core\mat.hpp, line 537 

UPDATE

If tracing this code, I see that constructor line calls the constructor

inline Mat::Mat(int _rows, int _cols, int _type, void* _data, size_t _step) 

Why? This prototype has 5 parameters, while I am providing 4 arguments.

Answer 1

How to fill Matrix with zeros in OpenCV?

To fill a pre-existing Mat object with zeros, you can use Mat::zeros()

Mat m1 = ...; m1 = Mat::zeros(1, 1, CV_64F); 

To intialize a Mat so that it contains only zeros, you can pass a scalar with value 0 to the constructor:

Mat m1 = Mat(1,1, CV_64F, 0.0); //                        ^^^^double literal 

The reason your version failed is that passing 0 as fourth argument matches the overload taking a void* better than the one taking a scalar.

Answer 2

use cv::mat::setto

img.setTo(cv::Scalar(redVal,greenVal,blueVal))