C++ 如何在 OpenCV 中用零填充矩阵？
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How to fill Matrix with zeros in OpenCV?
提问by Suzan Cioc
The code below causes an exception. Why?
下面的代码会导致异常。为什么？
#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:
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%\build\include\opencv2\core\mat.hpp, line 537
UPDATE
更新
If tracing this code, I see that constructor line calls the constructor
如果跟踪此代码，我会看到构造函数行调用构造函数
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.
为什么？这个原型有 5 个参数，而我提供了 4 个参数。
采纳答案by LovaBill
Because the last parameter is optional and also the data pointer should point somewhere appropriate:
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：
//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;
But better do it directly with this template-based constructor:
但最好直接使用这个基于模板的构造函数：
//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));
回答by juanchopanza
How to fill Matrix with zeros in OpenCV?
如何在 OpenCV 中用零填充矩阵？
To fill a pre-existing Matobject with zeros, you can use Mat::zeros()
Mat要用零填充预先存在的对象，您可以使用Mat::zeros()
Mat m1 = ...;
m1 = Mat::zeros(1, 1, CV_64F);
To intialize a Matso that it contains only zeros, you can pass a scalar with value 0to the constructor:
要初始化 aMat使其仅包含零，您可以将带有值的标量传递0给构造函数：
Mat m1 = Mat(1,1, CV_64F, 0.0);
// ^^^^double literal
The reason your version failed is that passing 0as fourth argument matches the overload taking a void*better than the one taking a scalar.
您的版本失败的原因是0作为第四个参数传递的重载void*比采用标量的重载更好。
回答by GPPK
use cv::mat::setto
img.setTo(cv::Scalar(redVal,greenVal,blueVal))
img.setTo(cv::Scalar(redVal,greenVal,blueVal))
回答by Nik Ved
If You are more into programming with templates, You may also do it this way...
如果您更喜欢使用模板进行编程，您也可以这样做...
template<typename _Tp>
... some algo ...
cv::Mat mat = cv::Mat_<_Tp>::zeros(rows, cols);
mat.at<_Tp>(i, j) = val;
回答by James Koo
回答by Shameel Mohamed
You can use this to fill zeroes in a Mat object already containing data:
您可以使用它在已经包含数据的 Mat 对象中填充零：
image1 = Scalar::all(0);
For eg, if you use it this way:
例如，如果您以这种方式使用它：
Mat image,image1;
image = imread("IMG_20160107_185956.jpg", CV_LOAD_IMAGE_COLOR); // Read the file
if(! image.data ) // Check for invalid input
{
cout << "Could not open or find the image" << std::endl ;
return -1;
}
cvtColor(image,image1,CV_BGR2GRAY);
image1 = Scalar::all(0);
It will work fine. But you cannot use this for uninitialised Mat. For that you can go for other options mentioned in above answers, like
它会正常工作。但是您不能将它用于未初始化的 Mat。为此，您可以选择上述答案中提到的其他选项，例如
Mat drawing = Mat::zeros( image.size(), CV_8UC3 );
回答by Lonewolf
Mat img;
垫 img;
img=Mat::zeros(size of image,CV_8UC3);
img=Mat::zeros（图像大小，CV_8UC3）；
if you want it to be of an image img1
如果你希望它是一个图像 img1
img=Mat::zeros(img1.size,CV_8UC3);
img=Mat::zeros(img1.size,CV_8UC3);
回答by Cynichniy Bandera
I presume you are talking about filling zeros of some existing mat? How about this? :)
我想你是在谈论填充一些现有垫子的零？这个怎么样？:)
mat *= 0;
垫 *= 0;
