我正在尝试为一些使用OpenCV的C 代码编写python包装器,但是我很难将结果(即OpenCV C Mat对象)返回给python解释器。
我查看了OpenCV的源代码,发现文件cv2.cpp具有转换功能,可以在PyObject *和OpenCV的Mat之间进行来回转换。我使用了这些转换函数,但是在尝试使用它们时遇到了分段错误。
对于使用OpenCV的python和C 代码的接口,我基本上需要一些建议/示例代码/在线参考,尤其是具有将OpenCV的C Mat返回给python解释器的功能,或者关于如何/在何处开始调查原因的建议分割错误的原因。
目前,我正在使用Boost Python来包装代码。
在此先感谢您的任何答复。
相关代码:
// This is the function that is giving the segmentation fault. PyObject* ABC::doSomething(PyObject* image) { Mat m; pyopencv_to(image, m); // This line gives segmentation fault. // Some code to create cppObj from CPP library that uses OpenCV cv::Mat processedImage = cppObj->align(m); return pyopencv_from(processedImage); }
转换函数取自OpenCV的源代码。转换代码使用“if(!PyArray_Check(o))…”在注释行中给出分段错误。
static int pyopencv_to(const PyObject* o, Mat& m, const char* name = "<unknown>", bool allowND=true) { if(!o || o == Py_None) { if( !m.data ) m.allocator = &g_numpyAllocator; return true; } if( !PyArray_Check(o) ) // Segmentation fault inside PyArray_Check(o) { failmsg("%s is not a numpy array", name); return false; } int typenum = PyArray_TYPE(o); int type = typenum == NPY_UBYTE ? CV_8U : typenum == NPY_BYTE ? CV_8S : typenum == NPY_USHORT ? CV_16U : typenum == NPY_SHORT ? CV_16S : typenum == NPY_INT || typenum == NPY_LONG ? CV_32S : typenum == NPY_FLOAT ? CV_32F : typenum == NPY_DOUBLE ? CV_64F : -1; if( type < 0 ) { failmsg("%s data type = %d is not supported", name, typenum); return false; } int ndims = PyArray_NDIM(o); if(ndims >= CV_MAX_DIM) { failmsg("%s dimensionality (=%d) is too high", name, ndims); return false; } int size[CV_MAX_DIM+1]; size_t step[CV_MAX_DIM+1], elemsize = CV_ELEM_SIZE1(type); const npy_intp* _sizes = PyArray_DIMS(o); const npy_intp* _strides = PyArray_STRIDES(o); bool transposed = false; for(int i = 0; i < ndims; i++) { size[i] = (int)_sizes[i]; step[i] = (size_t)_strides[i]; } if( ndims == 0 || step[ndims-1] > elemsize ) { size[ndims] = 1; step[ndims] = elemsize; ndims++; } if( ndims >= 2 && step[0] < step[1] ) { std::swap(size[0], size[1]); std::swap(step[0], step[1]); transposed = true; } if( ndims == 3 && size[2] <= CV_CN_MAX && step[1] == elemsize*size[2] ) { ndims--; type |= CV_MAKETYPE(0, size[2]); } if( ndims > 2 && !allowND ) { failmsg("%s has more than 2 dimensions", name); return false; } m = Mat(ndims, size, type, PyArray_DATA(o), step); if( m.data ) { m.refcount = refcountFromPyObject(o); m.addref(); // protect the original numpy array from deallocation // (since Mat destructor will decrement the reference counter) }; m.allocator = &g_numpyAllocator; if( transposed ) { Mat tmp; tmp.allocator = &g_numpyAllocator; transpose(m, tmp); m = tmp; } return true; } static PyObject* pyopencv_from(const Mat& m) { if( !m.data ) Py_RETURN_NONE; Mat temp, *p = (Mat*)&m; if(!p->refcount || p->allocator != &g_numpyAllocator) { temp.allocator = &g_numpyAllocator; m.copyTo(temp); p = &temp; } p->addref(); return pyObjectFromRefcount(p->refcount); }
我的python测试程序:
import pysomemodule # My python wrapped library. import cv2 def main(): myobj = pysomemodule.ABC("faces.train") # Create python object. This works. image = cv2.imread('61.jpg') processedImage = myobj.doSomething(image) cv2.imshow("test", processedImage) cv2.waitKey() if __name__ == "__main__": main()
我解决了这个问题,所以我想在这里与可能有相同问题的其他人分享。
基本上,要摆脱分段错误,我需要调用numpy的import_array()函数。
从python运行C ++代码的“高级”视图是这样的:
假设您foo(arg)在python中有一个函数,该函数是某些C 函数的绑定。当您调用时foo(myObj),必须有一些代码将python对象“ myObj”转换为您的C 代码可以执行的形式。通常使用SWIG或Boost :: Python之类的工具半自动创建此代码。(在下面的示例中,我使用Boost :: Python。)
foo(arg)
foo(myObj)
现在,foo(arg)是一些C 函数的python绑定。此C 函数将接收通用PyObject指针作为参数。您将需要C 代码才能将此PyObject指针转换为“等效” C 对象。就我而言,我的python代码将OpenCV图像的OpenCV numpy数组作为函数的参数传递。C 中的“等效”形式是OpenCV C Mat对象。OpenCV在cv2.cpp中提供了一些代码(如下所示),以将PyObject指针(代表numpy数组)转换为C ++ Mat。诸如int和string之类的简单数据类型不需要用户编写这些转换函数,因为它们由Boost :: Python自动转换。
PyObject
将PyObject指针转换为合适的C 形式后,C 代码可以对其执行操作。当必须将数据从C 返回到python时,会出现类似的情况,即需要C 代码将数据的C ++表示形式转换为的某种形式PyObject。Boost :: Python将把剩下的工作转换PyObject为相应的python形式。当foo(arg)以python返回结果时,其格式为python可用。而已。
下面的代码显示了如何包装C 类“ ABC”并公开其方法“ doSomething”,该方法从python获取一个numpy数组(用于图像),将其转换为OpenCV的C Mat,进行一些处理,然后将结果转换为PyObject *,并将其返回给python解释器。您可以公开任意数量的函数/方法(请参见下面的代码中的注释)。
abc.hpp:
#ifndef ABC_HPP #define ABC_HPP #include <Python.h> #include <string> class ABC { // Other declarations ABC(); ABC(const std::string& someConfigFile); virtual ~ABC(); PyObject* doSomething(PyObject* image); // We want our python code to be able to call this function to do some processing using OpenCV and return the result. // Other declarations }; #endif
abc.cpp:
#include "abc.hpp" #include "my_cpp_library.h" // This is what we want to make available in python. It uses OpenCV to perform some processing. #include "numpy/ndarrayobject.h" #include "opencv2/core/core.hpp" // The following conversion functions are taken from OpenCV's cv2.cpp file inside modules/python/src2 folder. static PyObject* opencv_error = 0; static int failmsg(const char *fmt, ...) { char str[1000]; va_list ap; va_start(ap, fmt); vsnprintf(str, sizeof(str), fmt, ap); va_end(ap); PyErr_SetString(PyExc_TypeError, str); return 0; } class PyAllowThreads { public: PyAllowThreads() : _state(PyEval_SaveThread()) {} ~PyAllowThreads() { PyEval_RestoreThread(_state); } private: PyThreadState* _state; }; class PyEnsureGIL { public: PyEnsureGIL() : _state(PyGILState_Ensure()) {} ~PyEnsureGIL() { PyGILState_Release(_state); } private: PyGILState_STATE _state; }; #define ERRWRAP2(expr) \ try \ { \ PyAllowThreads allowThreads; \ expr; \ } \ catch (const cv::Exception &e) \ { \ PyErr_SetString(opencv_error, e.what()); \ return 0; \ } using namespace cv; static PyObject* failmsgp(const char *fmt, ...) { char str[1000]; va_list ap; va_start(ap, fmt); vsnprintf(str, sizeof(str), fmt, ap); va_end(ap); PyErr_SetString(PyExc_TypeError, str); return 0; } static size_t REFCOUNT_OFFSET = (size_t)&(((PyObject*)0)->ob_refcnt) + (0x12345678 != *(const size_t*)"\x78\x56\x34\x12\0\0\0\0\0")*sizeof(int); static inline PyObject* pyObjectFromRefcount(const int* refcount) { return (PyObject*)((size_t)refcount - REFCOUNT_OFFSET); } static inline int* refcountFromPyObject(const PyObject* obj) { return (int*)((size_t)obj + REFCOUNT_OFFSET); } class NumpyAllocator : public MatAllocator { public: NumpyAllocator() {} ~NumpyAllocator() {} void allocate(int dims, const int* sizes, int type, int*& refcount, uchar*& datastart, uchar*& data, size_t* step) { PyEnsureGIL gil; int depth = CV_MAT_DEPTH(type); int cn = CV_MAT_CN(type); const int f = (int)(sizeof(size_t)/8); int typenum = depth == CV_8U ? NPY_UBYTE : depth == CV_8S ? NPY_BYTE : depth == CV_16U ? NPY_USHORT : depth == CV_16S ? NPY_SHORT : depth == CV_32S ? NPY_INT : depth == CV_32F ? NPY_FLOAT : depth == CV_64F ? NPY_DOUBLE : f*NPY_ULONGLONG + (f^1)*NPY_UINT; int i; npy_intp _sizes[CV_MAX_DIM+1]; for( i = 0; i < dims; i++ ) { _sizes[i] = sizes[i]; } if( cn > 1 ) { /*if( _sizes[dims-1] == 1 ) _sizes[dims-1] = cn; else*/ _sizes[dims++] = cn; } PyObject* o = PyArray_SimpleNew(dims, _sizes, typenum); if(!o) { CV_Error_(CV_StsError, ("The numpy array of typenum=%d, ndims=%d can not be created", typenum, dims)); } refcount = refcountFromPyObject(o); npy_intp* _strides = PyArray_STRIDES(o); for( i = 0; i < dims - (cn > 1); i++ ) step[i] = (size_t)_strides[i]; datastart = data = (uchar*)PyArray_DATA(o); } void deallocate(int* refcount, uchar*, uchar*) { PyEnsureGIL gil; if( !refcount ) return; PyObject* o = pyObjectFromRefcount(refcount); Py_INCREF(o); Py_DECREF(o); } }; NumpyAllocator g_numpyAllocator; enum { ARG_NONE = 0, ARG_MAT = 1, ARG_SCALAR = 2 }; static int pyopencv_to(const PyObject* o, Mat& m, const char* name = "<unknown>", bool allowND=true) { //NumpyAllocator g_numpyAllocator; if(!o || o == Py_None) { if( !m.data ) m.allocator = &g_numpyAllocator; return true; } if( !PyArray_Check(o) ) { failmsg("%s is not a numpy array", name); return false; } int typenum = PyArray_TYPE(o); int type = typenum == NPY_UBYTE ? CV_8U : typenum == NPY_BYTE ? CV_8S : typenum == NPY_USHORT ? CV_16U : typenum == NPY_SHORT ? CV_16S : typenum == NPY_INT || typenum == NPY_LONG ? CV_32S : typenum == NPY_FLOAT ? CV_32F : typenum == NPY_DOUBLE ? CV_64F : -1; if( type < 0 ) { failmsg("%s data type = %d is not supported", name, typenum); return false; } int ndims = PyArray_NDIM(o); if(ndims >= CV_MAX_DIM) { failmsg("%s dimensionality (=%d) is too high", name, ndims); return false; } int size[CV_MAX_DIM+1]; size_t step[CV_MAX_DIM+1], elemsize = CV_ELEM_SIZE1(type); const npy_intp* _sizes = PyArray_DIMS(o); const npy_intp* _strides = PyArray_STRIDES(o); bool transposed = false; for(int i = 0; i < ndims; i++) { size[i] = (int)_sizes[i]; step[i] = (size_t)_strides[i]; } if( ndims == 0 || step[ndims-1] > elemsize ) { size[ndims] = 1; step[ndims] = elemsize; ndims++; } if( ndims >= 2 && step[0] < step[1] ) { std::swap(size[0], size[1]); std::swap(step[0], step[1]); transposed = true; } if( ndims == 3 && size[2] <= CV_CN_MAX && step[1] == elemsize*size[2] ) { ndims--; type |= CV_MAKETYPE(0, size[2]); } if( ndims > 2 && !allowND ) { failmsg("%s has more than 2 dimensions", name); return false; } m = Mat(ndims, size, type, PyArray_DATA(o), step); if( m.data ) { m.refcount = refcountFromPyObject(o); m.addref(); // protect the original numpy array from deallocation // (since Mat destructor will decrement the reference counter) }; m.allocator = &g_numpyAllocator; if( transposed ) { Mat tmp; tmp.allocator = &g_numpyAllocator; transpose(m, tmp); m = tmp; } return true; } static PyObject* pyopencv_from(const Mat& m) { if( !m.data ) Py_RETURN_NONE; Mat temp, *p = (Mat*)&m; if(!p->refcount || p->allocator != &g_numpyAllocator) { temp.allocator = &g_numpyAllocator; m.copyTo(temp); p = &temp; } p->addref(); return pyObjectFromRefcount(p->refcount); } ABC::ABC() {} ABC::~ABC() {} // Note the import_array() from NumPy must be called else you will experience segmentation faults. ABC::ABC(const std::string &someConfigFile) { // Initialization code. Possibly store someConfigFile etc. import_array(); // This is a function from NumPy that MUST be called. // Do other stuff } // The conversions functions above are taken from OpenCV. The following function is // what we define to access the C++ code we are interested in. PyObject* ABC::doSomething(PyObject* image) { cv::Mat cvImage; pyopencv_to(image, cvImage); // From OpenCV's source MyCPPClass obj; // Some object from the C++ library. cv::Mat processedImage = obj.process(cvImage); return pyopencv_from(processedImage); // From OpenCV's source }
使用Boost Python创建python模块的代码。我从http://jayrambhia.wordpress.com/tag/boost/中获取了以下Makefile文件:
pysomemodule.cpp:
#include <string> #include<boost/python.hpp> #include "abc.hpp" using namespace boost::python; BOOST_PYTHON_MODULE(pysomemodule) { class_<ABC>("ABC", init<const std::string &>()) .def(init<const std::string &>()) .def("doSomething", &ABC::doSomething) // doSomething is the method in class ABC you wish to expose. One line for each method (or function depending on how you structure your code). Note: You don't have to expose everything in the library, just the ones you wish to make available to python. ; }
最后,Makefile(可以在Ubuntu上成功编译,但是应该可以在其他地方进行少量调整)。
PYTHON_VERSION = 2.7 PYTHON_INCLUDE = /usr/include/python$(PYTHON_VERSION) # location of the Boost Python include files and library BOOST_INC = /usr/local/include/boost BOOST_LIB = /usr/local/lib OPENCV_LIB = `pkg-config --libs opencv` OPENCV_CFLAGS = `pkg-config --cflags opencv` MY_CPP_LIB = lib_my_cpp_library.so TARGET = pysomemodule SRC = pysomemodule.cpp abc.cpp OBJ = pysomemodule.o abc.o $(TARGET).so: $(OBJ) g++ -shared $(OBJ) -L$(BOOST_LIB) -lboost_python -L/usr/lib/python$(PYTHON_VERSION)/config -lpython$(PYTHON_VERSION) -o $(TARGET).so $(OPENCV_LIB) $(MY_CPP_LIB) $(OBJ): $(SRC) g++ -I$(PYTHON_INCLUDE) -I$(BOOST_INC) $(OPENCV_CFLAGS) -fPIC -c $(SRC) clean: rm -f $(OBJ) rm -f $(TARGET).so
成功编译库后,目录中应该有一个文件“ pysomemodule.so”。将此lib文件放在python解释器可访问的位置。然后,您可以导入该模块并创建上述类“ ABC”的实例,如下所示:
import pysomemodule foo = pysomemodule.ABC("config.txt") # This will create an instance of ABC
现在,给定一个OpenCV numpy数组图像,我们可以使用以下命令调用C ++函数:
processedImage = foo.doSomething(image) # Where the argument "image" is a OpenCV numpy image.
请注意,您将需要Boost Python,Numpy dev和Python dev库来创建绑定。
以下两个链接中的NumPy文档在帮助人们理解转换代码中使用的方法以及为什么必须调用import_array()方面特别有用。特别是,官方的numpy文档有助于理解OpenCV的python绑定代码。
http://dsnra.jpl.nasa.gov/software/Python/numpydoc/numpy-13.html http://docs.scipy.org/doc/numpy/user/c-info.how-to- extend.html
希望这可以帮助。