如何在 OpenCV 中用零填充矩阵?

问题描述

下面的代码导致异常.为什么?

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;
    }

}

错误如下:

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%uildincludeopencv2coremat.hpp, line 537

更新

如果跟踪这段代码，我看到构造函数行调用了构造函数

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)

为什么?这个原型有 5 个参数，而我提供了 4 个参数.

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

推荐答案

因为最后一个参数是可选的，而且数据指针应该指向适当的地方:

Because the last parameter is optional and also the data pointer should point somewhere appropriate:

//inline Mat::Mat(int _rows, int _cols, int _type, void* _data, size_t _step)
double mydata[1];
Mat m1 = Mat(1,1, CV_64F, mydata); 
m1.at<double>(0,0) = 0;

但最好直接使用这个基于模板的构造函数:

But better do it directly with this template-based constructor:

//inline Mat::Mat(int _rows, int _cols, int _type, const Scalar& _s)
Mat m1 = Mat(1,1, CV_64F, cvScalar(0.));

//or even
Mat m1 = Mat(1,1, CV_64F, double(0));

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