基于opencv，开发摄像头播放程序

Posted 2022-06-28 yuanchenhui

前言 Windows下实现摄像视频捕捉有多种实现方式；各种方式的优劣，本文不做对比。但是，opencv是一款老牌开发库，在图像处理领域声名显赫。采用opencv来处理摄像视频，在性能和稳定性上，是有保障的。并且，opencv包含很多图像处理函数，可以更方便的对视频处理。

　　执行程序是用wpf开发的，所以先将opencv封装成c语言接口，以供调用。opencv也不可能提供现成的控件供wpf使用，两种不同的开发语言“沟通”起来有些困难。其实稍作变通，就可以实现摄像头播放功能。

1 对opencv封装

opencv的类VideoCapture封装了对摄像头的操作，使用起来也非常简单。

 bool open(int device); device为摄像头设备序号。

如果有多个摄像头，怎么知道哪个摄像头的序号那？可以通过如下函数，获取摄像头列表。摄像头在list中索引即为设备序号。

int GetCameraDevices(vector<wstring>& list)

    ICreateDevEnum *pDevEnum = NULL;
    IEnumMoniker *pEnum = NULL;
    int deviceCounter = 0;
    CoInitialize(NULL);
    HRESULT hr = CoCreateInstance(CLSID_SystemDeviceEnum, NULL,
        CLSCTX_INPROC_SERVER, IID_ICreateDevEnum,
        reinterpret_cast<void**>(&pDevEnum));

    if (SUCCEEDED(hr))
    
        // Create an enumerator for the video capture category.
        hr = pDevEnum->CreateClassEnumerator(
            CLSID_VideoInputDeviceCategory,
            &pEnum, 0);

        if (hr == S_OK) 

            //if (!silent)printf("SETUP: Looking For Capture Devices\\n");
            IMoniker *pMoniker = NULL;

            while (pEnum->Next(1, &pMoniker, NULL) == S_OK) 

                IPropertyBag *pPropBag;
                hr = pMoniker->BindToStorage(0, 0, IID_IPropertyBag,
                    (void**)(&pPropBag));

                if (FAILED(hr)) 
                    pMoniker->Release();
                    continue;  // Skip this one, maybe the next one will work.
                

                // Find the description or friendly name.
                VARIANT varName;
                VariantInit(&varName);
                hr = pPropBag->Read(L"Description", &varName, 0);

                if (FAILED(hr))
                    hr = pPropBag->Read(L"FriendlyName", &varName, 0);

                if (SUCCEEDED(hr)) 

                    hr = pPropBag->Read(L"FriendlyName", &varName, 0);

                    int count = 0;
                    wstring str2 = varName.bstrVal;
                    list.push_back(str2);
                

                pPropBag->Release();
                pPropBag = NULL;

                pMoniker->Release();
                pMoniker = NULL;

                deviceCounter++;
            

            pDevEnum->Release();
            pDevEnum = NULL;

            pEnum->Release();
            pEnum = NULL;
        
    
    return deviceCounter;

总之，使用opencv打开摄像头非常简单。

打开之后，就是获取摄像头图像。视频其实就是图像的集合；每秒钟获取25幅图像，将其在控件上显示，就是视频。

Mat cameraImg;
_pCapture >> cameraImg;

Mat类封装了对图像的操作。c#不可能操作Mat，需要将Mat中纯图像部分数据传递出来，图像才能被c#利用。

int Camera_GetImgData(INT64 handle, char* imgBuffer)

    CameraInfo *pCameraInfo = (CameraInfo*)handle;

    Mat cameraImg;
    *(pCameraInfo->_pCapture) >> cameraImg;

    if (!cameraImg.empty())
    
        int height = cameraImg.rows;int dataLen = height * cameraImg.step;
        memcpy(imgBuffer, cameraImg.data, dataLen);

        return 0;
    
    else
    
        return 1;
    

cameraImg.data中存有图像数据，data的大小可以根据图像的高度、每行图像的步幅计算出来。c#调用此函数后，imgBuffer存放图像数据。对数据imgBuffer处理后，就可以在控件上显示。

c语言对opencv封装函数列表如下：

extern "C"

    OpenCVCamera_API int Camera_GetCameraName(char* listName);

    OpenCVCamera_API INT64 Camera_CreateHandle();
    OpenCVCamera_API void Camera_CloseHandle(INT64 handle);

    OpenCVCamera_API BOOL Camera_IsOpen(INT64 handle);
    OpenCVCamera_API int Camera_Open(INT64 handle, int index);
    OpenCVCamera_API int Camera_Close(INT64 handle);

    OpenCVCamera_API int Camera_GetImgInfo(INT64 handle,int& width,int& height,int& channel,
        int& step, int& depth);
    OpenCVCamera_API int Camera_GetImgData(INT64 handle, char* imgBuffer);

    //flipCode >0: 沿y-轴翻转, 0: 沿x-轴翻转, <0: x、y轴同时翻转
    OpenCVCamera_API int Camera_GetImgData_Flip(INT64 handle, char* imgBuffer, int flipCode);
    OpenCVCamera_API int Camera_ImgData_Compress(int rows, int cols, int type, void* imgBuffer,
        int param,void* destBuffer,int* destLen);

函数定义如下

class CameraInfo

public:
    VideoCapture * _pCapture;

    CameraInfo()
    
        _pCapture = NULL;
    

    ~CameraInfo()
    
        if (_pCapture != NULL)
            delete _pCapture;
    
;

int Camera_GetCameraName(char* listName)

    vector<wstring> listName2;
    GetCameraDevices(listName2);

    wstring all;
    for (size_t i = 0; i < listName2.size(); i++)
    
        all += listName2[i];
        all += L";";
    

    int n = all.length();
    memcpy(listName, all.data(), n * 2);
    return listName2.size();


INT64 Camera_CreateHandle()

    CameraInfo *pCameraInfo = new CameraInfo();
    return (INT64)pCameraInfo;


void Camera_CloseHandle(INT64 handle)

    CameraInfo *pCameraInfo = (CameraInfo*)handle;
    delete pCameraInfo;


BOOL Camera_IsOpen(INT64 handle)

    CameraInfo *pCameraInfo = (CameraInfo*)handle;
    if (pCameraInfo->_pCapture == NULL)
        return FALSE;

    BOOL open = pCameraInfo->_pCapture->isOpened();
    return open;


int Camera_Open(INT64 handle, int index)

    Camera_Close(handle);
    CameraInfo *pCameraInfo = (CameraInfo*)handle;
    pCameraInfo->_pCapture = new VideoCapture();

    bool open = pCameraInfo->_pCapture->open(index);
    if (open)
        return 0;
    return 1;


int Camera_Close(INT64 handle)

    CameraInfo *pCameraInfo = (CameraInfo*)handle;
    if (pCameraInfo->_pCapture == NULL)
        return 0;

    delete pCameraInfo->_pCapture;
    pCameraInfo->_pCapture = NULL;
    return 0;



//depth == enumCV_8U=0,CV_8S=1,CV_16U=2,CV_16S=3,CV_32S=4,CV_32F=5,CV_64F=6  
int Camera_GetImgInfo(INT64 handle, int& width, int& height, int& channel, int& step, int& depth)

    CameraInfo *pCameraInfo = (CameraInfo*)handle;

    Mat cameraImg;
    *(pCameraInfo->_pCapture) >> cameraImg;
    if (!cameraImg.empty())
    
        height = cameraImg.rows;
        width = cameraImg.cols;
        channel = cameraImg.channels();
        step = cameraImg.step;
        depth = cameraImg.depth();
        return 0;
    
    else
    
        return 1;
    


int Camera_GetImgData(INT64 handle, char* imgBuffer)

    CameraInfo *pCameraInfo = (CameraInfo*)handle;

    Mat cameraImg;
    *(pCameraInfo->_pCapture) >> cameraImg;

    if (!cameraImg.empty())
    
        int height = cameraImg.rows;
        int width = cameraImg.cols;
        int channel = cameraImg.channels();
        int dataLen = height * cameraImg.step;
        memcpy(imgBuffer, cameraImg.data, dataLen);

        return 0;
    
    else
    
        return 1;
    


int Camera_GetImgData_Flip(INT64 handle, char* imgBuffer, int flipCode)

    CameraInfo *pCameraInfo = (CameraInfo*)handle;

    Mat cameraImg;
    *(pCameraInfo->_pCapture) >> cameraImg;

    if (!cameraImg.empty())
    
        Mat dest;
        if (flipCode != 100)
        
            flip(cameraImg, dest, flipCode);
        
        else
        
            dest = cameraImg;
        

        int height = dest.rows;
        int width = dest.cols;
        int channel = dest.channels();
        int dataLen = height * cameraImg.step;
        memcpy(imgBuffer, dest.data, dataLen);

        return 0;
    
    else
    
        return 1;
    


BOOL  MatToCompressData(const Mat& mat, std::vector<unsigned char>& buff)

    if (mat.empty())
    
        return FALSE;
    

    //提前分配内存 否则会报错
    int n = mat.rows*mat.cols*mat.channels();
    buff.reserve(n * 2);

    std::vector<int> param(2);
    param.push_back(CV_IMWRITE_JPEG_QUALITY);
    param.push_back(95);// default(95) 0-100
    return cv::imencode(".jpg", mat, buff, param);



int Camera_ImgData_Compress(int rows, int cols, int type, void* imgBuffer,
    int param, void* destBuffer, int* destLen)

    Mat src(rows, cols, type, imgBuffer);

    std::vector<unsigned char> buff;
    MatToCompressData(src, buff);
    if (*destLen < buff.size())
        return -1;

    memcpy(destBuffer, buff.data(), buff.size());
    *destLen = buff.size();

    return 0;

2 WPF实现视频播放

WPF的Image控件实现图像的显示。实现视频播放的逻辑为：设定一个定时器（时间间隔为40毫秒），每隔一段时间从opencv获取图像，在控件中显示。

 <Image x:Name="imageVideoPlayer" Stretch="Uniform" ></Image>

实现图像显示代码

  BitmapSource bitmapSource = _openCVCamera.GetBitmapSource();
            if (bitmapSource == null)
                return false;

 imageVideoPlayer.Source = bitmapSource;

实现图像显示的关键是构建BitmapSource，暨：如何从opencv中获取图像数据构建BitmapSource。

  //获取图像数据
   if (!GetImgData(out byte[] imgData))
                    return null;

   //构建WriteableBitmap
   WriteableBitmap img = new WriteableBitmap(_imgWidth, _imgHeight, 96, 96, PixelFormats.Bgr24, null);
   img.WritePixels(new Int32Rect(0, 0, _imgWidth, _imgHeight),
                   imgData, img.BackBufferStride, 0);
   img.Freeze();

至此，就可以显示摄像头图像了。