對於單通道影象：

void Invert1(){
    Mat src,dest;
    src = imread("lena.jpg");
    if(!src.data){
        cout << "影象載入失敗" << endl;
        return ;
    }
    namedWindow("原影象",CV_WINDOW_AUTOSIZE);
    imshow("原影象",src);

    cvtColor(src,dest,COLOR_BGR2GRAY);

    int rows = src.rows;
    int
 
 cols = src.cols;

    //單通道影象的反色
    for(int row = 0;row<rows;row++){
        for(int col = 0;col<cols;col++){
            dest.at<uchar>(row,col) = 255 - dest.at<uchar>(row,col);
        }
    }
    namedWindow("單通道，反色後",CV_WINDOW_AUTOSIZE);
    imshow("單通道，反色後",dest);

    cvWaitKey();
}
 

對於三通道影象：

void Invert2(){
    Mat src;
    src = imread("lena.jpg");
    if(!src.data){
        cout << "影象載入失敗" << endl;
        return ;
    }
    namedWindow("原影象",CV_WINDOW_AUTOSIZE);
    imshow("原影象",src);
    int rows = src.rows;
    int cols = src.cols;
    cout << rows << "\t"
 
 << cols << endl;
    Mat dest;
    dest.create(src.size(),src.type());

    for(int row = 0;row<rows;row++){
        for(int col=0;col<cols;col++){
            int b = src.at<Vec3b>(row,col)[0];
            int g = src.at<Vec3b>(row,col)[1];
            int r = src.at<Vec3b>(row,col)[2];

            dest.at<Vec3b>(row,col)[0] = 255-b;
            dest.at<Vec3b>(row,col)[1] = 255-g;
            dest.at<Vec3b>(row,col)[2] = 255-r;

        }
    }

    namedWindow("三通道，反色後",CV_WINDOW_AUTOSIZE);
    imshow("三通道，反色後",dest);
    cvWaitKey();
}

OpenCV提供的函式bitwise_not(src,dest):

void Invert3(){
    Mat src,dest;
    src = imread("lena.jpg");
    if(!src.data){
        cout << "影象載入失敗" << endl;
        return ;
    }
    namedWindow("原影象",CV_WINDOW_AUTOSIZE);
    imshow("原影象",src);

    cv::bitwise_not(src,dest);

    namedWindow("反色後",CV_WINDOW_AUTOSIZE);
    imshow("反色後",dest);
    cvWaitKey();
}

不同於使用cvtColor()函式，我們可以自己對畫素操作實現灰度圖的顯示：

void GrayShow(){
    Mat src;
    src = imread("lena.jpg");
    if(!src.data){
        cout << "影象載入失敗" << endl;
        return ;
    }
    namedWindow("原影象",CV_WINDOW_AUTOSIZE);
    imshow("原影象",src);
    int rows = src.rows;
    int cols = src.cols;

    Mat dest  = Mat(src.rows,src.cols,0);
    for(int row = 0;row<rows;row++){
        for(int col=0;col<cols;col++){
            int b = src.at<Vec3b>(row,col)[0];
            int g = src.at<Vec3b>(row,col)[1];
            int r = src.at<Vec3b>(row,col)[2];

            dest.at<uchar>(row,col) = max(r,max(g,b));//選擇bgr中最大值
            //dest.at<uchar>(row,col) = min(r,min(g,b));//選擇bgr中最小值
        }
    }

    namedWindow("min,灰度圖",CV_WINDOW_AUTOSIZE);
    imshow("min,灰度圖",dest);
    cvWaitKey();
}