将cv :: Mat转换为std :: vector而不进行复制 [英] Convert cv::Mat to std::vector without copying

问题描述

我有这个功能：

void foo(cv::Mat &mat){
  float *p = mat.ptr<float>(0);
  //modify mat values through p
}

我有这段代码会调用该函数：

And I have this code that calls the function:

void bar(std::vector<unsigned char> &vec){
  //...
  cv::Mat res(m, n, CV_32FC1, (void *)&workspace.front());
}

但是，上面的代码存在性能问题： vec 可能未对齐。实际上，英特尔编译器说引用* out具有未对齐的访问权限。我希望这是原因。

However, the code above has a performance problem: vec isn't probably aligned. In fact, the Intel compiler says that reference *out has unaligned access. I hope that this is the reason.

顺便说一句，我在这个问题， cv :: Mat 将要对齐。因此，一个简单的解决方法是：

Btw, as I found out in this question, cv::Mat is going to be aligned. So a simple workaround would be to:

1. 创建 cv :: Mat res（m，n）


2. 调用 foo（m）;


3. 分配 vec 指向 m.ptr< float>（0）
的指针

1. Create cv::Mat res(m,n)
2. Call foo(m);
3. Assign the vec pointer to m.ptr<float>(0)

正如您可以想象的那样，这里的性能至关重要，因此深层复制是毫无疑问的。

As you can imagine, performance here are crucial, so deep-copies are out of questions.

我尝试了这个问题：

vec = res.data;

但是我遇到了编译器错误。此外，我不知道上面的代码是否要进行（低效的）复制，或者只是通过 vec 更改指向的数据。

But I get a compiler error. Besides, I don't know if this code above is going to do an (inefficient) copy, or just change the pointed data by vec.

我该如何顺利进行？否则，将意识到另一种解决方法。

How can I do this smoothly? Otherwise, another workaround would be appreciated.

推荐答案

看看此处

std::vector<uchar> array;
if (mat.isContinuous()) {
  array.assign(mat.datastart, mat.dataend);
} else {
  for (int i = 0; i < mat.rows; ++i) {
    array.insert(array.end(), mat.ptr<uchar>(i), mat.ptr<uchar>(i)+mat.cols);
  }
}

//p.s.: For cv::Mats of other types, like CV_32F, you should do like this:

std::vector<float> array;
if (mat.isContinuous()) {
  array.assign((float*)mat.datastart, (float*)mat.dataend);
} else {
  for (int i = 0; i < mat.rows; ++i) {
    array.insert(array.end(), (float*)mat.ptr<uchar>(i), (float*)mat.ptr<uchar>(i)+mat.cols);
  }
}

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