摘要: 以opencv驱动摄像头, 并处理图像, 将结果传递给C#, 不涉及图像数据Mat的传递. 工程主体为C#, 封装opencv为dll, 进行调用. 开发环境用VS2019

系统简化: 为了能够更具体地描述openCV C++与C#混合编程, 对系统进行简化. 目标是用简单的C#窗体程序, 读取摄像头, 并显示原始图像, 算法处理后, 显示结果图像. 不涉及图像数据传递, 也就无法在窗体中重绘图像, 显示窗口仍用opencv的HighGUI模块.

openCV 程序设计

全局变量

由于不传递图像Mat, openCV程序应在作用域内处理图像, 就需要用到全局变量. 主要定义有:

• VideoCapture
• frame

摄像头初始化

void initCamera(int cameraIndex, double frameWidth, double frameHeight, double fps)
{
    camera.open(cameraIndex);
    if(!camera.isOpened())
    {
        cerr << "Couldn't open camera." << endl;
    }
    camera.set(cv::CAP_PROP_FRAME_WIDTH, frameWidth);      // 宽度
    camera.set(cv::CAP_PROP_FRAME_HEIGHT, frameHeight);    // 高度
    camera.set(cv::CAP_PROP_FPS, fps);                     // 帧率
}

摄像头高级设置(注意备份, 谨慎更改)

void setCameraParams(double brightness, double contrast, double saturation, double hue, double gain, double exposure)
{
    //打印摄像头参数
    cout << "\n参数修改前：" << endl;
    printf("brightness = %.2f\n", camera.get(cv::CAP_PROP_BRIGHTNESS));
    printf("contrast = %.2f\n", camera.get(cv::CAP_PROP_CONTRAST));
    printf("saturation = %.2f\n", camera.get(cv::CAP_PROP_SATURATION));
    printf("hue = %.2f\n", camera.get(cv::CAP_PROP_HUE));
    printf("gain = %.2f\n", camera.get(cv::CAP_PROP_GAIN));
    printf("exposure = %.2f\n", camera.get(cv::CAP_PROP_EXPOSURE));
    // 修改摄像头参数
    camera.set(cv::CAP_PROP_BRIGHTNESS, brightness);        // 亮度
    camera.set(cv::CAP_PROP_CONTRAST, contrast);            // 对比度
    camera.set(cv::CAP_PROP_SATURATION, saturation);        // 饱和度
    camera.set(cv::CAP_PROP_HUE, hue);                      // 色调
    camera.set(cv::CAP_PROP_GAIN, gain);                    // 增益
    camera.set(cv::CAP_PROP_EXPOSURE, exposure);            // 曝光度
    //打印摄像头参数
    cout << "\n参数修改后：" << endl;
    printf("brightness = %.2f\n", camera.get(cv::CAP_PROP_BRIGHTNESS));
    printf("contrast = %.2f\n", camera.get(cv::CAP_PROP_CONTRAST));
    printf("saturation = %.2f\n", camera.get(cv::CAP_PROP_SATURATION));
    printf("hue = %.2f\n", camera.get(cv::CAP_PROP_HUE));
    printf("gain = %.2f\n", camera.get(cv::CAP_PROP_GAIN));
    printf("exposure = %.2f\n", camera.get(cv::CAP_PROP_EXPOSURE));
}

读取帧并显示

void readFrame()
{
    camera >> frame;
    cv::imshow("camera", frame);
    cv::waitKey(1);
}

图像处理

void processingImage()
{
    cv::cvtColor(frame, frame, cv::COLOR_BGR2GRAY);
    cv::Canny(frame, frame, 100, 200);
    cv::imshow("processor", frame);
    cv::waitKey(1);
}

关闭显示

void closeCamera(string winName)
{
    if(winName == "camera")
        cv::destroyWindow("camera");
    else if(winName == "processor")
        cv::destroyWindow("processor");
    else
        ;// do nothing
}

头文件声明

由于是导出为dll, 需要特别的语法支持

extern "C" __declspec(dllexport) void initCamera(int cameraIndex, double frameWidth, double frameHeight, double fps);
extern "C" __declspec(dllexport) void readFrame();
extern "C" __declspec(dllexport) void processingImage();
extern "C" __declspec(dllexport) void closeCamera(string winName);

生成dll

• 更改项目属性, 设置配置类型为 dll, 如图. 然后右键生成或Ctrl+Shift+B, 即可在输出目录看到dll文件
• 由于该dll依赖于opencv库, 所以还应包含opencv的dll. 如果是独立模块, 则需包括所有调用的; 如果是集合成了world文件, 就只需包含"opencv_world411.dll"即可. 参见博客: 封装opencv的函数成dll，独立调用

C#窗体程序

建立窗体项目

注意不要选错类型, 具体步骤可参考微软官方教程: Create a Windows Forms app in Visual Studio with C#

导入dll

如同导出声明一样, 需要特定的导入格式

// 初始化摄像头
[DllImport("ImageTracker.dll", EntryPoint = "initCamera", CallingConvention = CallingConvention.Cdecl)]
public static extern void initCamera(int cameraIndex, double frameWidth, double frameHeight, double fps);

有博客提到, 用reference的方法添加dll, 未尝试. Visual Studio 在 C# 项目添加动态链接库 dll

调用dll

完整可运行项目已经打包：Project_CPP_CSharp.zip 需要在VSPropertySheet中适配自己的opencv环境

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace Camera
{
    public partial class FormCamera : Form
    {
        // 初始化摄像头
        [DllImport("ImageProcessing.dll", EntryPoint = "initCamera", CallingConvention = CallingConvention.Cdecl)]
        public static extern void initCamera(int cameraIndex, double frameWidth, double frameHeight, double fps);            
            
        // 读取图像并显示
        [DllImport("ImageProcessing.dll", EntryPoint = "readFrame", CallingConvention = CallingConvention.Cdecl)]
        public static extern void readFrame();
        
        // 处理图像并显示
        [DllImport("ImageProcessing.dll", EntryPoint = "processingImage", CallingConvention = CallingConvention.Cdecl)]
        public  static extern void processingImage();

        // 关闭窗口
        [DllImport("ImageProcessing.dll", EntryPoint = "closeCamera", CallingConvention = CallingConvention.Cdecl)]
        public static extern void closeCamera(string winName);


        public FormCamera()
        {
            InitializeComponent();
            ImageProcessing();
        }


        private void ImageProcessing()
        {
            initCamera(0, -1, -1, -1);
            for(int i = 0; i <= 10000; i++)
            {
                readFrame();
                processingImage();
            }
            closeCamera("camera");
            closeCamera("processor");
        }
    }
}

其中遇到的问题

• dll模块不存在: 将两个dll都放入C#的生成目录. 参见生成dll小节的参考文献: 封装opencv的函数成dll，独立调用
• dll格式无效: 将调试平台设置为x64, 因为openCV只支持64位. 参见博客: 试图加载格式不正确的程序。 (异常来自 HRESULT:0x8007000B)
• HighGUI窗体无响应: 设置为主线程, 即在imshow后追加waitKey(1), 参见博客: OpenCV使用cv::imshow在子线程中更新图片不刷新
• 打不开视频：因为C#的string无法传给C++的string，只能将C#中的string路径传给C++中的char*