Transform buffer to cv::Mat without copy.

edit

I try to convert buffered data in cv::Mat (it's originaly to make a python binding numpy array to cv::Mat) my code here https://github.com/edmBernard/pybind1...

in python when we do channel slicing the internal strides in "simply" set to 3 instead of 1 (there is no copy)

a = eb.read_image("test.png")
b=a[:,:,0]

so b is not continuous

In full opencv C++, it's equivalente to try to get only one channel from a CV_8UC3 image. I try this but it don't seem to work as I think

// arr is my buffer (raw data)
cv::Mat(cv::Size(shape[1], shape[0]), 
        dtype_cv, 
        arr.mutable_data(), 
        image_from_file.elemSize()*image_from_file.cols*3);
// another solution with the same result
// here info.ptr is my buffer
cv::Mat(ndims,
        &shape[0],
        dtype
        info.ptr
        &strides[0]);

edit : there is some misunderstanding of my problem I try to be cleaner