发送图像 opencv c++ 到 python

Question

我用python打开图片，发给C++function处理，返回图片。 如何从 c ++ function 正确获取图片？

分段错误

代码示例：

C++

// t_lib.cpp 
#include "opencv2/opencv.hpp"

extern "C" unsigned char*  getfg(int rows,int cols, unsigned char* fdata)
//extern "C" void getfg(int rows,int cols, unsigned char* fdata)
{
    cv::Mat frame = cv::Mat(rows, cols, CV_8UC3, (void *) fdata);
    // Work 
    //cv::imshow("Display window C++", frame);
    //cv::waitKey(0);

    // do something

    return frame.data; //fdata;
}

Python 2.7

# test.py
import cv2
import numpy as np
import ctypes
lib = ctypes.cdll.LoadLibrary('./lib.so')

def getfg(img):
    ptr = lib.getfg(img.shape[0], img.shape[1], img.ctypes.data_as(ctypes.POINTER(ctypes.c_ubyte)))
    buf = (ctypes.c_ubyte * img.shape[0] * img.shape[1]  * 3).from_address(ptr)
    res = np.ndarray(buffer=buf, dtype=np.uint8, shape=(img.shape[0], img.shape[1], 3), order="C")
    return res

f = cv2.imread("sample.jpg")
#gray_image = cv2.cvtColor(f, cv2.COLOR_BGR2GRAY)
AS = getfg(f)
print AS.shape
#np.array(AS)[0]
cv2.imshow("Window Python", AS)
cv2.waitKey(0)

汇编：

g++ -c -fPIC t_lib.cpp -o lib -lX11 $(pkg-config opencv --cflags --libs) -I/usr/include/python2.7 -I/usr/lib/python2.7;

g++ -shared -Wl,-soname,lib.so -o lib.so lib -lopencv_core -lopencv_highgui -lopencv_imgproc

查看 opencv 库的命令：

pkg-config opencv --cflags --libs

output：

-I/usr/include/opencv -lopencv_shape -lopencv_stitching 
-lopencv_superres -lopencv_videostab -lopencv_aruco 
-lopencv_bgsegm -lopencv_bioinspired -lopencv_ccalib
-lopencv_datasets -lopencv_dpm -lopencv_face 
-lopencv_freetype -lopencv_fuzzy -lopencv_hdf 
-lopencv_line_descriptor -lopencv_optflow -lopencv_video 
-lopencv_plot -lopencv_reg -lopencv_saliency -lopencv_stereo 
-lopencv_structured_light -lopencv_phase_unwrapping -lopencv_rgbd 
-lopencv_viz -lopencv_surface_matching -lopencv_text 
-lopencv_ximgproc -lopencv_calib3d -lopencv_features2d 
-lopencv_flann -lopencv_xobjdetect -lopencv_objdetect 
-lopencv_ml -lopencv_xphoto -lopencv_highgui 
-lopencv_videoio -lopencv_imgcodecs -lopencv_photo 
-lopencv_imgproc -lopencv_core

版本 c++ OpenCV 3.2.0

Answer 1

你必须编译该C ++代码到一个共享库，根据本然后写一个包装

Answer 2

您可以使用的方法之一，使用 memcpy

python3.x main.py

import cv2
import numpy as np
import ctypes

cv_lib = ctypes.CDLL("./cpp_function.so")

def opencv_cpp_operation(im):
    ND_POINTER_1 = np.ctypeslib.ndpointer(dtype=np.float64, 
                                        ndim=im.ndim,
                                        flags="C")
    cv_lib.opencv_op.argtypes = [ND_POINTER_1,ctypes.c_size_t]
    cv_lib.opencv_op.restype = np.ctypeslib.ndpointer(dtype=np.float64, ndim=im.ndim, shape=im.shape, flags="C")
    ret_img = cv_lib.opencv_op(im, *im.shape, im.shape[0] * im.shape[1])
    return ret_img

im = cv2.imread("./imagepath.jpg", 0)
np_array = opencv_cpp_operation(im)

c++ cpp_function.cpp

编译使用g++ -shared -fPIC cpp_function.cpp -o cpp_function.so -I /usr/include/opencv4/ -L /usr/lib -lopencv_core -lopencv_imgproc

#include <iostream>
#include <opencv2/opencv.hpp>

using namespace cv;
extern "C" {
    double* opencv_op(double *a1, size_t a1_h, size_t a1_w, int size){
            cv::Mat A(a1_h,a1_w,CV_64F);
            std::memcpy(A.data, a1, a1_h*a1_w*sizeof(double));   

            // Now use Mat A for your processing than return it python

            cv::Mat C(a1_h,a1_w,CV_64F);
            C = A * 2; 
            double* ret_arr = new double[size]; 
            std::memcpy(ret_arr, C.data, a2_h*a2_w*sizeof(double));
            
            return ret_arr;

    }
}