OpenCV 3.9及以上，
IplImage 与 Mat 转换出现问题
./src/image_opencv.cpp: In function ‘image mat_to_image(cv::Mat)’:
./src/image_opencv.cpp:63:20: error: conversion from ‘cv::Mat’ to non-scalar type ‘IplImage {aka _IplImage}’ requested
IplImage ipl = m;
^
compilation terminated due to -Wfatal-errors.
Makefile:86: recipe for target 'obj/image_opencv.o' failed
make: *** [obj/image_opencv.o] Error 1
测试程序