#include <opencv2/core.hpp>
#include <opencv2/imgcodecs.hpp>
#include <opencv2/highgui.hpp>
#include <iostream>
using namespace cv;
using namespace std;

// 記錄時間信息
void PrintMs(const char *text = "")
{
    static long long last = 0;
    long long cur = getTickCount();
    
 
if (last == 0)
    {
        last = cur;
        return;
    }
    long long ms = 0;
    ms = ((double)(cur - last) / getTickFrequency()) * 1000;
    if (*text != 0)
    {
        printf("%s = %dms\n", text,ms);
    }
    last = getTickCount();
}
int main(int argc, char *argv[])
{
    Mat mat(
 
3000, 4000, CV_8UC3);
    //mat.create(3000, 4000, CV_8UC3);
    //元素大小字節數
    int es = mat.elemSize();
    int size = mat.rows*mat.cols*es;
    
    //地址遍歷連續的Mat
    PrintMs();
    for (int i = 0; i < size; i += es)
    {
        mat.data[i] = 255;    //B
        mat.data[i + 1] = 100;//G
        mat.data[i + 2
 
] = 100;//R
    }
    PrintMs("mat.data ms");

    //地址遍歷不一定連續的Mat
    for (int row = 0; row < mat.rows; row++)
    {
        for (int col = 0; col < mat.cols; col++)
        {
            (&mat.data[row*mat.step])[col*es] = 0;//B
            (&mat.data[row*mat.step])[col*es+1] = 0;//G
            (&mat.data[row*mat.step])[col*es+2] = 255;//R
        }
    }
    PrintMs("mat.step ms");


    //使用ptr遍歷Mat
    for (int row = 0; row < mat.rows; row++)
    {
        for (int col = 0; col < mat.cols; col++)
        {
            Vec3b *c = mat.ptr<Vec3b>(row, col);
            c->val[0] = 0;        //B
            c->val[1] = 255;    //G
            c->val[2] = 0;        //R
        }
    }
    PrintMs("mat.ptr ");
    try
    {
        //使用at來遍歷
        for (int row = 0; row < mat.rows; row++)
        {
            for (int col = 0; col < mat.cols; col++)
            {
                Vec3b &m = mat.at<Vec3b>(row, col);
                m[0] = 100;
                m[1] = 100;
                m[2] = 100;
            }
        }
        PrintMs("mat.at");
    }
    catch (Exception &ex)
    {
        cout << ex.what() << endl;
    }
    
    //通過叠代器來遍歷
    PrintMs("");
    auto it = mat.begin<Vec3b>();
    auto it_end = mat.end<Vec3b>();
    for (; it != it_end; it++)
    {
        (*it).val[0] = 0;    //B
        (*it).val[1] = 0;    //G
        (*it).val[2] = 255;    //R
    }
    PrintMs("mat.itr");


    namedWindow("mat");
    imshow("mat", mat);
    waitKey(0);

    return 0;
}

Opencv --- 圖像像素遍歷的各種方法