Mat imread(const string& filename, intflags=1 );

flags:
enum
{
/* 8bit, color or not */
   CV_LOAD_IMAGE_UNCHANGED  =-1,
/* 8bit, gray */
   CV_LOAD_IMAGE_GRAYSCALE  =0,
/* ?, color */
   CV_LOAD_IMAGE_COLOR      =1,
/* any depth, ? */
   CV_LOAD_IMAGE_ANYDEPTH   =2,
/* ?, any color */
   CV_LOAD_IMAGE_ANYCOLOR   =4
};

Mat image0=imread("dota.jpg",CV_LOAD_IMAGE_ANYDEPTH | CV_LOAD_IMAGE_ANYCOLOR);//載入最真實的圖像
Mat image1=imread("dota.jpg",0);//載入灰度圖
Mat image2=imread("dota.jpg",199);//載入3通道的彩色圖像
Mat logo=imread("dota_logo.jpg");//載入3通道的彩色圖像

void namedWindow(const string& winname,int flags=WINDOW_AUTOSIZE ); 

void imshow(const string& winname, InputArray mat);

import cv2 as cv
import numpy as np
image = cv.imread("/home/stoair/Opencv/Images/1.png", 4)
cv.namedWindow("initial",cv.WINDOW_NORMAL)
cv.namedWindow("after",cv.WINDOW_NORMAL)
height = image.shape[0]
width = image.shape[1]
cv.imshow("initial",image)
for i in range(height):
	for j in range(width):
		(b, g, r) = image[i, j]
		ave = b/3 + g/3 + r/3
		image[i, j] = (ave, ave, ave)

cv.imshow("after",image) 
cv.waitKey(0)

#include<opencv2/core/core.hpp>
#include<opencv2/highgui/highgui.hpp>
#include <opencv2/imgcodecs.hpp> 
#include <opencv2/opencv.hpp>

using namespace cv;

int main()
{
    Mat image0 = imread("/home/stoair/Opencv/Images/1.png", 4);
    namedWindow("initial", WINDOW_NORMAL);
    namedWindow("change", WINDOW_NORMAL);
    imshow("initial", image0);

    int height = image0.rows;
    int width = image0.cols;
    for(int i = 0; i < height; i++){
        for(int j = 0; j < width; j++){
            unsigned char b = image0.at<Vec3b>(i, j)[0];
            unsigned char g = image0.at<Vec3b>(i, j)[1];
            unsigned char r = image0.at<Vec3b>(i, j)[2];
            unsigned char ave = b/3 + g/3 +r/3;
            image0.at<Vec3b>(i, j)[0] = ave;
            image0.at<Vec3b>(i, j)[1] = ave;
            image0.at<Vec3b>(i, j)[2] = ave;
        }
    }

    imshow("change", image0);
    waitKey(0);
    return 0;
}