Opencv learning example code 3.2.4 LUT

#include <opencv2/objdetect.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv2/videoio.hpp>
#include <iostream>
#include <iomanip>
#include <opencv2/opencv.hpp>
#include <vector>
#include <opencv2/imgproc/types_c.h>
using namespace cv;
using namespace std;
int main(int argc, char** argv)
{
    uchar lutFirst[256];
    for(int i=0;i<256;i++)
    {
        if(i<=100)
	{
	    lutFirst[i]=0;
        } 
        if(i>100&&i<=200)
        {
            lutFirst[i]=100;
        }
        if(i>200)
        {
            lutFirst[i]=255;
        }
    }
    Mat lutOne(1,256,CV_8UC1,lutFirst);
    uchar lutSecond[256];
    for(int i=0;i<256;i++)
    {
        if(i<=100)
        {
            lutSecond[i]=0;
        }
        if(i>100&&i<=150)
        {
            lutSecond[i]=100;
        }
        if(i>150&&i<=200)
        {
            lutSecond[i]=150;
        }
        if(i>200)
        {
            lutSecond[i]=255;
        }
    }
    Mat lutTwo(1,256,CV_8UC1,lutSecond);
    uchar lutThird[256];
    for(int i=0;i<256;i++)
    {
        if(i<100)
        {
            lutThird[i]=100;
        }
        if(i>100&&i<=200)
        {
            lutThird[i]=200;
        }
        if(i>200)
        {
            lutThird[i]=255;
        }
    }

    Mat lutThree(1,256,CV_8UC1,lutThird);
    vector<Mat> mergeMats;
    mergeMats.push_back(lutOne); 
    mergeMats.push_back(lutTwo);
    mergeMats.push_back(lutThree);
    Mat LutTree;
    merge(mergeMats,LutTree);
   Mat img=imread("lena.png");
    if(img.empty())
    {
        cout<<"open faile"<<endl;
        return -1;
    }
    Mat gray,out0,out1,out2;
    cvtColor(img,gray,COLOR_BGR2GRAY);
    LUT(gray,lutOne,out0);
    LUT(img,lutOne,out1);
    LUT(img,LutTree,out2);
    imshow("out0",out0);
   imshow("out1",out1);
   imshow("out2",out2);
    
    waitKey(0);
    return 0;
}