樹莓派小而強大，有非常多的應用場景。這裡分享下使用樹莓派，攝像頭，以及C和Python程式碼來實現一個條形碼掃描工具。之前分享過如何把OpenCV Python獲取的影象傳遞到C層處理，會用到裡面的程式碼。

測試環境

• 裝置: Raspberry Pi 3
• 系統: RASPBIAN JESSIE WITH PIXEL

準備工作

• Dynamsoft Barcode Reader for Raspberry Pi
• Python 2.7.0
• OpenCV 3.0.0
• Raspberry Pi 2 or 3
• USB webcam

編譯和安裝

如何在樹莓派上編譯安裝OpenCV

1. 下載原始碼。

2. 安裝依賴庫：

sudo apt-get install cmake
sudo apt-get install libjpeg-dev libtiff5-dev libjasper-dev libpng12-dev
sudo apt-get install libavcodec-dev libavformat-dev libswscale-dev libv4l-dev
sudo apt-get install libxvidcore-dev libx264-dev
sudo apt-get install python-dev

3. 設定編譯環境：

cd ~/opencv-3.0.0/
mkdir build
cd
 
 build
cmake -D CMAKE_BUILD_TYPE=RELEASE \
                -D CMAKE_INSTALL_PREFIX=/usr/local \
                -D INSTALL_C_EXAMPLES=ON \
                -D INSTALL_PYTHON_EXAMPLES=ON \
                -D OPENCV_EXTRA_MODULES_PATH=~/opencv_contrib-3.0.0/modules \
                -D BUILD_EXAMPLES=ON ..

4. 編譯安裝OpenCV：

make -j4
sudo make install

生成的動態連結庫會被安裝到/usr/local/lib/python2.7/dist-packages/cv2.so。

使用Dynamsoft Barcode SDK建立Python擴充套件

1. 下載SDK。

2. 建立符號連結：

sudo ln –s <Your dbr path>/lib/libDynamsoftBarcodeReader.so /usr/lib/libDynamsoftBarcodeReader.so

3. 編輯setup.py。設定標頭檔案和庫檔案路徑：

include_dirs=["/usr/lib/python2.7/dist-packages/numpy/core/include/numpy", "<Your dbr path>/include"],
library_dirs=['<Your dbr path>/lib'],

4. 編譯安裝Python擴充套件：

sudo python setup.py build install

實現decodeBuffer介面

底層的C程式碼是從windows版本上移植過來的。需要新增一些定義：

typedef unsigned long DWORD;
typedef long LONG;
typedef unsigned short WORD;
 
typedef struct tagBITMAPINFOHEADER {
  DWORD biSize;
  LONG biWidth;
  LONG biHeight;
  WORD biPlanes;
  WORD biBitCount;
  DWORD biCompression;
  DWORD biSizeImage;
  LONG biXPelsPerMeter;
  LONG biYPelsPerMeter;
  DWORD biClrUsed;
  DWORD biClrImportant;
} BITMAPINFOHEADER;

把Python的numpy資料轉換成C。然後通過底層的介面檢測識別條形碼：

#include<ndarraytypes.h>
 
static PyObject *
decodeBuffer(PyObject *self, PyObject *args){
    PyObject *o;
    if (!PyArg_ParseTuple(args, "O", &o))
        return NULL;
 
    PyObject *ao = PyObject_GetAttrString(o, "__array_struct__");
    PyObject *retval;
 
    if ((ao == NULL) || !PyCObject_Check(ao)) {
        PyErr_SetString(PyExc_TypeError, "object does not have array interface");
        return NULL;
    }
 
    PyArrayInterface *pai = (PyArrayInterface*)PyCObject_AsVoidPtr(ao);
    if (pai->two != 2) {
        PyErr_SetString(PyExc_TypeError, "object does not have array interface");
        Py_DECREF(ao);
        return NULL;
    }
 
    // Construct data with header info and image data 
    char *buffer = (char*)pai->data; // The address of image data
    int width = pai->shape[1];       // image width
    int height = pai->shape[0];      // image height
    int size = pai->strides[0] * pai->shape[0]; // image size = stride * height
    char *total = (char *)malloc(size + 40); // buffer size = image size + header size
    memset(total, 0, size + 40);
    BITMAPINFOHEADER bitmap_info = {40, width, height, 0, 24, 0, size, 0, 0, 0, 0};
    memcpy(total, &bitmap_info, 40);
 
    // Copy image data to buffer from bottom to top
    char *data = total + 40;
    int stride = pai->strides[0];
    int i = 1;
    for (; i <= height; i++) {
        memcpy(data, buffer + stride * (height - i), stride);
        data += stride;
    }
 
    // Dynamsoft Barcode Reader initialization
    __int64 llFormat = (OneD | QR_CODE | PDF417 | DATAMATRIX);
    int iMaxCount = 0x7FFFFFFF;
    ReaderOptions ro = {0};
    pBarcodeResultArray pResults = NULL;
    ro.llBarcodeFormat = llFormat;
    ro.iMaxBarcodesNumPerPage = iMaxCount;
    printf("width: %d, height: %d, size:%d\n", width, height, size);
    int iRet = DBR_DecodeBuffer((unsigned char *)total, size + 40, &ro, &pResults);
    printf("DBR_DecodeBuffer ret: %d\n", iRet);
    free(total); // Do not forget to release the constructed buffer 
     
    // Get results
    int count = pResults->iBarcodeCount;
    pBarcodeResult* ppBarcodes = pResults->ppBarcodes;
    pBarcodeResult tmp = NULL;
    retval = PyList_New(count); // The returned Python object
    PyObject* result = NULL;
    i = 0;
    for (; i < count; i++)
    {
        tmp = ppBarcodes[i];
        result = PyString_FromString(tmp->pBarcodeData);
        printf("result: %s\n", tmp->pBarcodeData);
        PyList_SetItem(retval, i, Py_BuildValue("iN", (int)tmp->llFormat, result)); // Add results to list
    }
    // release memory
    DBR_FreeBarcodeResults(&pResults);
 
    Py_DECREF(ao);
    return retval;
}

樹莓派條形碼掃描應用

如何用OpenCV Python設定幀率以及每一幀的寬高

• CV_CAP_PROP_FRAME_WIDTH: Width of the frames in the video stream.
• CV_CAP_PROP_FRAME_HEIGHT: Height of the frames in the video stream.
• CV_CAP_PROP_FPS: Frame rate.

如果設定失敗，顯示這些常量沒有定義，可以直接輸入值：

vc = cv2.VideoCapture(0)
vc.set(5, 30)  #set FPS
vc.set(3, 320) #set width
vc.set(4, 240) #set height

如何在Python應用中使用decodeBuffer()：

while True:
        cv2.imshow(windowName, frame)
        rval, frame = vc.read();
        results = decodeBuffer(frame)
        if (len(results) > 0):
            print "Total count: " + str(len(results))
            for result in results:
                print "Type: " + types[result[0]]
                print "Value: " + result[1] + "\n"
 
        # 'ESC' for quit
        key = cv2.waitKey(20)
        if key == 27:
            break

執行樹莓派條形碼掃描應用

1. 用樹莓派2或者3連線一個USB攝像頭。

2. 執行程式：

python app.py

原始碼