树莓派小而强大，有非常多的应用场景。这里分享下使用树莓派，摄像头，以及C和Python代码来实现一个条形码扫描工具。之前分享过如何把OpenCV Python获取的图像传递到C层处理，会用到里面的代码。

测试环境

• 设备: Raspberry Pi 3
• 系统: RASPBIAN JESSIE WITH PIXEL

准备工作

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

编译和安装

如何在树莓派上编译安装OpenCV

1. 下载源代码。

2. 安装依赖库：

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. 设置编译环境：

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. 编译安装OpenCV：

make -j4
sudo make install

生成的动态链接库会被安装到/usr/local/lib/python2.7/dist-packages/cv2.so。

使用Dynamsoft Barcode SDK创建Python扩展

1. 下载SDK。

2. 创建符号链接：

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

3. 编辑setup.py。设置头文件和库文件路径：

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

4. 编译安装Python扩展：

sudo python setup.py build install

实现decodeBuffer接口

底层的C代码是从windows版本上移植过来的。需要添加一些定义：

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数据转换成C。然后通过底层的接口检测识别条形码：

#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 dataint width = pai->shape[1];       // image widthint height = pai->shape[0];      // image heightint size = pai->strides[0] * pai->shape[0]; // image size = stride * heightchar *total = (char *)malloc(size + 40); // buffer size = image size + header sizememset(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 topchar *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 resultsint count = pResults->iBarcodeCount;pBarcodeResult* ppBarcodes = pResults->ppBarcodes;pBarcodeResult tmp = NULL;retval = PyList_New(count); // The returned Python objectPyObject* 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 memoryDBR_FreeBarcodeResults(&pResults);Py_DECREF(ao);return retval;
}

树莓派条形码扫描应用

如何用OpenCV Python设置帧率以及每一帧的宽高

可以参考官方文档Property identifier:

• 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.

如果设置失败，显示这些常量没有定义，可以直接输入值：

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应用中使用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 quitkey = cv2.waitKey(20)if key == 27:break

运行树莓派条形码扫描应用

1. 用树莓派2或者3连接一个USB摄像头。

2. 执行程序：

python app.py

源码

https://github.com/yushulx/opencv-python-webcam-barcode-reader/tree/master/raspberrypi