Fastest way to extract individual pixel data?

Question

I have to get information about the scalar value of a lot of pixels on a gray-scale image using OpenCV. It will be traversing hundreds of thousands of pixels so I need the

Answer 1

With regards to Martin's post, you can actually check if the memory is allocated continuously using the isContinuous() method in OpenCV's Mat object. The following is a common idiom for ensuring the outer loop only loops once if possible:

#include 

using namespace cv;

int main(void)
{

    Mat img = imread("test.jpg");
    int rows = img.rows;
    int cols = img.cols;

    if (img.isContinuous())
    {
        cols = rows * cols; // Loop over all pixels as 1D array.
        rows = 1;
    }

    for (int i = 0; i < rows; i++)
    {
        Vec3b *ptr = img.ptr(i);
        for (int j = 0; j < cols; j++)
        {
            Vec3b pixel = ptr[j];
        }
    }

    return 0;
}