Convert Mat to Array/Vector in OpenCV

I am novice in OpenCV. Recently, I have troubles finding OpenCV functions to convert from Mat to Array. I researched with .ptr and .at methods available in OpenCV APIs, but I could not get proper data. I would like to have direct conversion from Mat to Array(if available, if not to Vector). I need OpenCV functions because the code has to be undergo high level synthesis in Vivado HLS. Please help.

If the memory of the Mat mat is continuous (all its data is continuous), you can directly get its data to a 1D array:

std::vector<uchar> array(mat.rows*mat.cols*mat.channels());
if (mat.isContinuous())
    array = mat.data;

Otherwise, you have to get its data row by row, e.g. to a 2D array:

uchar **array = new uchar*[mat.rows];
for (int i=0; i<mat.rows; ++i)
    array[i] = new uchar[mat.cols*mat.channels()];

for (int i=0; i<mat.rows; ++i)
    array[i] = mat.ptr<uchar>(i);

---

UPDATE: It will be easier if you're using std::vector, where you can do like this:

std::vector<uchar> array;
if (mat.isContinuous()) {
  // array.assign(mat.datastart, mat.dataend); // <- has problems for sub-matrix like mat = big_mat.row(i)
  array.assign(mat.data, mat.data + mat.total()*mat.channels());
} else {
  for (int i = 0; i < mat.rows; ++i) {
    array.insert(array.end(), mat.ptr<uchar>(i), mat.ptr<uchar>(i)+mat.cols*mat.channels());
  }
}

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); // <- has problems for sub-matrix like mat = big_mat.row(i)
  array.assign((float*)mat.data, (float*)mat.data + mat.total()*mat.channels());
} else {
  for (int i = 0; i < mat.rows; ++i) {
    array.insert(array.end(), mat.ptr<float>(i), mat.ptr<float>(i)+mat.cols*mat.channels());
  }
}

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UPDATE2: For OpenCV Mat data continuity, it can be summarized as follows:

• Matrices created by imread(), clone(), or a constructor will always be continuous.
• The only time a matrix will not be continuous is when it borrows data (except the data borrowed is continuous in the big matrix, e.g. 1. single row; 2. multiple rows with full original width) from an existing matrix (i.e. created out of an ROI of a big mat).

Please check out this code snippet for demonstration.