Opencv in memory Mat representation

Question

I know that in memory opencv represents Mat objects as one big array. So if I have 3 channels mat of dimension 200x200 then In memory it will store this mat in an array of size

Answer 1

I found other answers a bit confusing: mat.step is the size of a row in bytes, not in (double) elements, and it does already take into consideration the number of channels. To access val you should use:

double* array = (double*) mat.data; // was (double) mat.data in the question
double value = array[ ((mat.step)/mat.elemSize1())*c+mat.channels()*r+ch]; // (mat.step)/mat.elemSize1() is the actual row length in (double) elements

You can verify this and other approaches comparing them with the .at<> operator as follows:

#include 
#include 

using namespace cv;
using namespace std;

int main()
{
const int w0=5;
const int h=3;
const int w=4;
double data[w0*h*3];
for (int y=0; y(r,c);
cout<<"the 3 channels at row="<