如何把OpenCV Python获取的图像传递到C层处理

用OpenCV Python来开发，如果想要用到一些C/C++的图像处理库，就需要创建Python的C/C++扩展，然后把数据从Python传递到底层处理。这里分享下如何在C/C++层获取数据。

参考原文：How to Convert OpenCV Image Data from Python to C

作者：Xiao Ling

翻译：yushulx

开发环境

• Dynamsoft Barcode Reader 4.2
• Python version: 2.7.0
• OpenCV version: 2.4.10. Download cv2.pyd
• Windows 10
• USB webcam

Python C/C++扩展

把DynamsoftBarcodeReaderx86.dll和cv2.pyd拷贝到目录Python27\Lib\site-packages。

OpenCV Python获取的图像数据类型是numpy.ndarray:

> rval, frame = vc.read();> print type(frame)> <type 'numpy.ndarray'>

在C层我们希望能获取到数据的指针。查看OpenCV源码文件opencv\modules\python\src2\cv2.cv.hpp可以找到方法：

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 * height

这样就可以了。现在可以用这个数据做点事情，比如调用barcode接口来做检测。我依然用Dynamsoft Barcode Reader SDK做示例。首先需要构建一下数据：

char *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];for (int i = 1; i <= height; i++) {    memcpy(data, buffer + stride * (height - i), stride);    data += stride;}

接下来就可以检测barcode了：

// 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;    for (int i = 0; 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);

在Windows上构建Python扩展需要先设置一下，不然会出错。我使用Visual Studio 2015。命令行如下：

SET VS90COMNTOOLS=%VS140COMNTOOLS%python setup.py build install

好了。现在可以用Python脚本来调用了。首先打开摄像头：

import cv2from dbr import *import time vc = cv2.VideoCapture(0)

接下来读取一帧的数据：

cv2.imshow(windowName, frame)rval, frame = vc.read();

现在可以实时检测barcode了：

initLicense("<license>") # Invalid license is fine.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"

 

源码

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