OpenCV4入门教程089：视频直方图反向投影

我们在OpenCV4入门教程085：图像直方图反向投影介绍过单张图片的直方图反向投影，本文实现视频的直方图反向投影实时计算显示。

// Program to illustrate histogram backprojection 
// Author: Samarth Manoj Brahmbhatt, University of Pennsylvania

//---------------------------------【头文件、命名空间包含部分】----------------------------
//      描述：包含程序所使用的头文件和命名空间
//------------------------------------------------------------------------------------------------
#include <opencv2/opencv.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
using namespace cv;
using namespace std;


//-----------------------------------【全局变量声明部分】---------------------------------------
//      描述：声明全局变量
//---------------------------------------------------------------------------------------------------
Mat frame_hsv, frame, mask;
MatND hist; //2D直方图
int conn = 4, val = 255, flags = conn + (val << 8) + FLOODFILL_MASK_ONLY;
bool selected = false;
// 直方图相关参数
float hrange[] = {0, 179}, srange[] = {0, 255};
const float *ranges[] = {hrange, srange};


//-----------------------------------【on_mouse( )函数】-------------------------------------
//      描述：鼠标回调函数
//-------------------------------------------------------------------------------------------------
void on_mouse(int event, int x, int y, int, void *) {
    if(event != EVENT_LBUTTONDOWN) return;

    selected = true;

    // floodFill
    Point p(x, y);
    mask = Scalar::all(0);
    floodFill(frame, mask, p, Scalar(255, 255, 255), 0, Scalar(10, 10, 10), Scalar(10, 10, 10), flags);
    Mat _mask = mask.rowRange(1, mask.rows-1).colRange(1, mask.cols-1);

    // number of bins in the histogram for each channel
    int histSize[] = {50, 50}, channels[] = {0, 1};

    // calculate and normalize histogram
    calcHist(&frame_hsv, 1, channels, _mask, hist, 2, histSize, ranges);
    normalize(hist, hist, 0, 255, NORM_MINMAX, -1, Mat());
}



//-----------------------------------【main( )函数】--------------------------------------------
//      描述：控制台应用程序的入口函数，我们的程序从这里开始
//-------------------------------------------------------------------------------------------------
int main( ) 
{
    //从摄像头读入视频
    VideoCapture cap(0);

    //检测是否读取成功
    if(!cap.isOpened()) {
        cout << "Capture could not be opened succesfully" << endl;
        return -1;
    }

    namedWindow("Video");
    namedWindow("Backprojection");

    setMouseCallback("Video", on_mouse);

    while(char(waitKey(1)) != 'q' && cap.isOpened()) {
        cap >> frame;
        if(!selected) mask.create(frame.rows+2, frame.cols+2, CV_8UC1);
        // Check if the video is over
        if(frame.empty()) {
            cout << "Video over" << endl;
            break;
        }
        cvtColor(frame, frame_hsv, COLOR_BGR2HSV);

        // backproject on the HSV image
        Mat frame_backprojected = Mat::zeros(frame.size(), CV_8UC1);        
        if(selected) {
            int channels[] = {0, 1};
            calcBackProject(&frame_hsv, 1, channels, hist, frame_backprojected, ranges);
        }

        imshow("Video", frame);
        imshow("Backprojection", frame_backprojected);
    }

    return 0;
}