OpenCv dnn module －实时图像分类

配置环境：OpenCv3.4, vs2013（x64）,Win7。
用OpenCv dnn module 实时检测摄像头，视频和图像的分类示例
原代码为：https://docs.opencv.org/3.4.0/da/d9d/tutorial_dnn_yolo.html，
https://github.com/pjreddie/darknet/tree/master/data，可以下载分类文件。根据不同的model,选择不同的names。
https://pjreddie.com/darknet/yolo/,可下载model的cfg文件和weights文件。

// Brief Sample of using OpenCV dnn module in real time with device capture, video and image.

#include <opencv2/dnn.hpp>
#include <opencv2/dnn/shape_utils.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv2/highgui.hpp>
#include <fstream>
#include <iostream>
#include <algorithm>
#include <cstdlib>

using namespace std;
using namespace cv;
using namespace cv::dnn;

static const char* about =
"This sample uses You only look once (YOLO)-Detector (https://arxiv.org/abs/1612.08242) to detect objects on camera/video/image.
"
"Models can be downloaded here: https://pjreddie.com/darknet/yolo/
"
"Default network is 416x416.
"
"Class names can be downloaded here: https://github.com/pjreddie/darknet/tree/master/data
";

static const char* params =
"{ help           | false | print usage         }"
"{ cfg            | model_cfg/yolo.cfg | model configuration }"   //模型配置文件
"{ model          | model_weights/yolo.weights | model weights       }" //模型权重文件
"{ camera_device  | 0     | camera device number}"　　　　　　//摄像头
"{ source         | pic/person.jpg | video or image for detection}"　　　图片路径
"{ save           |       | file name output}"　　　　//可设置保存文件路径
"{ fps            | 3     | frame per second }"
"{ style          | box   | box or line style draw }"
"{ min_confidence | 0.24  | min confidence      }"　　//最小置信阀值
"{ class_names    | names/coco.names | File with class names, [PATH-TO-DARKNET]/data/coco.names }";　　//分类文件

int main(int argc, char** argv)
{
    CommandLineParser parser(argc, argv, params);

    if (parser.get<bool>("help"))
    {
        cout << about << endl;
        parser.printMessage();
        return 0;
    }

    String modelConfiguration = parser.get<String>("cfg");
    String modelBinary = parser.get<String>("model");

    dnn::Net net;
    try {
        //! [Initialize network]
        net = readNetFromDarknet(modelConfiguration, modelBinary);
        //! [Initialize network]
    }
    catch (cv::Exception& e) {
        std::cerr << "Exception: " << e.what() << std::endl;
        if (net.empty())
        {
            cerr << "Can't load network by using the following files: " << endl;
            cerr << "cfg-file:     " << modelConfiguration << endl;
            cerr << "weights-file: " << modelBinary << endl;
            cerr << "Models can be downloaded here:" << endl;
            cerr << "https://pjreddie.com/darknet/yolo/" << endl;
            exit(-1);
        }
    }


    VideoCapture cap;
    VideoWriter writer;
    int codec = CV_FOURCC('M', 'J', 'P', 'G');
    double fps = parser.get<float>("fps");
    if (parser.get<String>("source").empty())
    {
        int cameraDevice = parser.get<int>("camera_device");
        cap = VideoCapture(cameraDevice);
        if (!cap.isOpened())
        {
            cout << "Couldn't find camera: " << cameraDevice << endl;
            return -1;
        }
    }
    else
    {
        cap.open(parser.get<String>("source"));
        if (!cap.isOpened())
        {
            cout << "Couldn't open image or video: " << parser.get<String>("video") << endl;
            return -1;
        }
    }

    if (!parser.get<String>("save").empty())
    {
        writer.open(parser.get<String>("save"), codec, fps, Size((int)cap.get(CAP_PROP_FRAME_WIDTH), (int)cap.get(CAP_PROP_FRAME_HEIGHT)), 1);
    }

    vector<String> classNamesVec;
    ifstream classNamesFile(parser.get<String>("class_names").c_str());
    if (classNamesFile.is_open())
    {
        string className = "";
        while (std::getline(classNamesFile, className))
            classNamesVec.push_back(className);
    }

    String object_roi_style = parser.get<String>("style");

    for (;;)
    {
        Mat frame;
        cap >> frame; // get a new frame from camera/video or read image
        
        if (frame.empty())
        {
            waitKey();
            break;
        }

        if (frame.channels() == 4)
            cvtColor(frame, frame, COLOR_BGRA2BGR);

        //! [Prepare blob]
        Mat inputBlob = blobFromImage(frame, 1 / 255.F, Size(416, 416), Scalar(), true, false); //Convert Mat to batch of images
        //! [Prepare blob]

        //! [Set input blob]
        net.setInput(inputBlob, "data");                   //set the network input
        //! [Set input blob]

        //! [Make forward pass]
        Mat detectionMat = net.forward("detection_out");   //compute output
        //! [Make forward pass]

        vector<double> layersTimings;
        double tick_freq = getTickFrequency();
        double time_ms = net.getPerfProfile(layersTimings) / tick_freq * 1000;
        putText(frame, format("FPS: %.2f ; time: %.2f ms", 1000.f / time_ms, time_ms),
            Point(20, 20), 0, 0.5, Scalar(0, 0, 255));

        float confidenceThreshold = parser.get<float>("min_confidence");
        for (int i = 0; i < detectionMat.rows; i++)
        {
            const int probability_index = 5;
            const int probability_size = detectionMat.cols - probability_index;
            float *prob_array_ptr = &detectionMat.at<float>(i, probability_index);

            size_t objectClass = max_element(prob_array_ptr, prob_array_ptr + probability_size) - prob_array_ptr;
            float confidence = detectionMat.at<float>(i, (int)objectClass + probability_index);

            if (confidence > confidenceThreshold)
            {
                float x_center = detectionMat.at<float>(i, 0) * frame.cols;
                float y_center = detectionMat.at<float>(i, 1) * frame.rows;
                float width = detectionMat.at<float>(i, 2) * frame.cols;
                float height = detectionMat.at<float>(i, 3) * frame.rows;
                Point p1(cvRound(x_center - width / 2), cvRound(y_center - height / 2));
                Point p2(cvRound(x_center + width / 2), cvRound(y_center + height / 2));
                Rect object(p1, p2);

                Scalar object_roi_color(0, 255, 0);

                if (object_roi_style == "box")
                {
                    rectangle(frame, object, object_roi_color);
                }
                else
                {
                    Point p_center(cvRound(x_center), cvRound(y_center));
                    line(frame, object.tl(), p_center, object_roi_color, 1);
                }

                String className = objectClass < classNamesVec.size() ? classNamesVec[objectClass] : cv::format("unknown(%d)", objectClass);
                String label = format("%s: %.2f", className.c_str(), confidence);
                int baseLine = 0;
                Size labelSize = getTextSize(label, FONT_HERSHEY_SIMPLEX, 0.5, 1, &baseLine);
                rectangle(frame, Rect(p1, Size(labelSize.width, labelSize.height + baseLine)),
                    object_roi_color, CV_FILLED);
                putText(frame, label, p1 + Point(0, labelSize.height),
                    FONT_HERSHEY_SIMPLEX, 0.5, Scalar(0, 0, 0));
            }
        }
        if (writer.isOpened())
        {
            writer.write(frame);
        }

        imshow("YOLO: Detections", frame);
        if (waitKey(1) >= 0) break;
    }

    return 0;
} // main