C++ 在 OpenCV 中更新 Mat 的子矩阵
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Updating a submatrix of Mat in OpenCV
提问by Carlos Cachalote
I am working with OpenCV and C++. I have a matrix X like this
我正在使用 OpenCV 和 C++。我有一个这样的矩阵 X
Mat X = Mat::zeros(13,6,CV_32FC1);
and I want to update just a submatrix 4x3 of it, but I have doubts on how to access that matrix in an efficient way.
我只想更新它的一个 4x3 子矩阵，但我怀疑如何以有效的方式访问该矩阵。
Mat mat43= Mat::eye(4,3,CV_32FC1); //this is a submatrix at position (4,4)
Do I need to change element by element?
我需要逐个元素更改吗？
回答by Jav_Rock
One of the quickest ways is setting a header matrix pointing to the range of columns/rows you want to update, like this:
最快的方法之一是设置指向要更新的列/行范围的标题矩阵，如下所示：
Mat aux = X.colRange(4,7).rowRange(4,8); // you are pointing to submatrix 4x3 at X(4,4)
Now, you can copy your matrix to aux (but actually you will be copying it to X, because aux is just a pointer):
现在，您可以将矩阵复制到 aux（但实际上您将其复制到 X，因为 aux 只是一个指针）：
mat43.copyTo(aux);
Thats it.
就是这样。
回答by Sam
First, you have to create a matrix that points to the original one:
首先，您必须创建一个指向原始矩阵的矩阵：
Mat orig(13,6,CV_32FC1, Scalar::all(0));
Mat roi(orig(cv::Rect(1,1,4,3))); // now, it points to the original matrix;
Mat otherMatrix = Mat::eye(4,3,CV_32FC1);
roi.setTo(5); // OK
roi = 4.7f; // OK
otherMatrix.copyTo(roi); // OK
Keep in mind that anyoperations that involves direct attribution, with the "=" sign from another matrix will change the roi matrix source from orig to that other matrix.
请记住，任何涉及直接归因的操作，带有来自另一个矩阵的“=”符号都会将 roi 矩阵源从 orig 更改为另一个矩阵。
// Wrong. Roi will point to otherMatrix, and orig remains unchanged
roi = otherMatrix;
