OpenCV像素级操作，灰度图像以及三色图像的反色处理

#include <opencv2/opencv.hpp>
#include <iostream>
#include <math.h>
using namespace cv;
using namespace std;

int main()
{
    Mat src;
    //原图
    src = imread(".//pic//test.jpg",IMREAD_UNCHANGED);
    if (src.empty())
    {
        cout << "can not load image" << endl;
        return -1;
    }
    namedWindow("input", CV_WINDOW_AUTOSIZE);
    imshow("input", src);
    
    //单通道图像反色处理
    Mat gray_src;
    cvtColor(src, gray_src, CV_BGR2GRAY);
    namedWindow("input", CV_WINDOW_AUTOSIZE);
    imshow("output", gray_src);
    int height = gray_src.rows;
    int width = gray_src.cols;
    /*for (int row = 0; row < height; row++)
    {
        for (int col = 0; col < width; col++)
        {
            int gray = gray_src.at<uchar>(row, col);
            gray_src.at<uchar>(row, col) = 255 - gray;
        }
    }
    imshow("反色", gray_src);*/

    //三通道图像的反色
    Mat dst;
    dst.create(src.size(), src.type());
    height = src.rows;
    width = src.cols;
    int nc = src.channels();
    //b,g,r 三通道
    int b;
    int g;
    int r;
    /*for (int row = 0; row < height; row++)
    {
        for (int col = 0; col < width; col++)
        {
            b = src.at<Vec3b>(row, col)[0];
            g= src.at<Vec3b>(row, col)[1];
            r = src.at<Vec3b>(row, col)[2];

            dst.at<Vec3b>(row, col)[0] = 255 - b;
            dst.at<Vec3b>(row, col)[1] = 255 - g;
            dst.at<Vec3b>(row, col)[2] = 255 - r;
        }
    }*/
    //api函数
    //bitwise_not(src, dst);
    //只保留红色通道的值
    for (int row = 0; row < height; row++)
    {
        for (int col = 0; col < width; col++)
        {
            b = src.at<Vec3b>(row, col)[0];
            g = src.at<Vec3b>(row, col)[1];
            r = src.at<Vec3b>(row, col)[2];

            dst.at<Vec3b>(row, col)[0] = 0;
            dst.at<Vec3b>(row, col)[1] = 0;
            dst.at<Vec3b>(row, col)[2] = r;
        }
    }
    imshow("三通道反色", dst);

    waitKey(0);
    return 0;
}