Ubuntu 18.04 配置 OpenCV 3.4.5 并编写测试代码

1.什么是OpenCV？

OpenCV是一个基于BSD许可（开源）发行的跨平台计算机视觉库，可以运行在Linux、Windows、Android和Mac OS操作系统上。它轻量级而且高效——由一系列 C 函数和少量 C++ 类构成，同时提供了Python、Ruby、MATLAB等语言的接口，实现了图像处理和计算机视觉方面的很多通用算法。
OpenCV用C++语言编写，它的主要接口也是C++语言，但是依然保留了大量的C语言接口。该库也有大量的Python、Java and MATLAB/OCTAVE（版本2.5）的接口。这些语言的API接口函数可以通过在线文档获得。如今也提供对于C#、Ch、Ruby,GO的支持。
——摘自百度

2.准备工作

首先,要更新 Ubuntu 的库

sudo apt-get update
sudo apt-get upgrade

然后安装一些 OpenCV 会用的库（这一步一定要认真做，否则后面会出现各种莫名其妙的错误！！！）

sudo apt-get install build-essential cmake libgtk2.0-dev libtiff4-dev libjasper-dev libavformat-dev libswscale-dev libavcodec-dev libjpeg62-dev pkg-config ffmpeg

在这一步中可能会遇到报错：

没有可用的软件包 libtiff4-dev，但是它被其它的软件包引用了。
这可能意味着这个缺失的软件包可能已被废弃，
或者只能在其他发布源中找到
然而下列软件包会取代它：
libtiff5-dev:i386 libtiff5-dev

解决方案是（其实是随便选了第二个…）：

sudo apt-get install libtiff5-dev

尤其是 libgtk2.0-dev 和 pkg-config 这两个库，否则在后面运行例程时会报错：

terminate called after throwing an instance of ‘cv::Exception’
what(): OpenCV(3.4.5) /home/cxy/文档/opencv-3.4.5/modules/highgui/src/window.cpp:617: error: (-2:Unspecified error) The function is not implemented. Rebuild the library with Windows, GTK+ 2.x or Carbon support. If you are on Ubuntu or Debian, install libgtk2.0-dev and pkg-config, then re-run cmake or configure script in function ‘cvNamedWindow’

如果忘记了装上面的某个库，在补装了以后要重新执行第4部分中的内容才可以正常编译工程。

3.OpenCV 下载

直接从官网提供的链接下载就行：OpenCV source download
下载解压后放在合适的位置，进入解压目录，进行如下操作，为OpenCV的编译作准备：

mkdir release
cd release

4.编译 OpenCV

首先，设置 cmake 编译参数：

sudo cmake …

然后开始编译 OpenCV：

sudo make
sudo make install

注：编译第一步可能耗时比较久，建议找点其他事做！

5.配置环境变量

网上可以查到很多种方法，这里提供一种亲测可行的方法，仅供参考：

sudo gedit /etc/ld.so.conf.d/opencv.conf

在文件 opencv.conf 内的末尾添加 “/usr/local/lib” 并保存；
更新系统的共享链接库：

sudo ldconfig

下一步：

sudo gedit /etc/bash.bashrc

在 bash.bashrc 的末尾添加 “export PKG_CONFIG_PATH=$PKG_CONFIG_PATH:/usr/local/lib/pkgconfig”

source /etc/bash.bashrc

至此，OpenCV环境搭建完毕（大功告成.jpg）。

6.编写测试项目

一开始以为配好环境，写一个 cpp 文件就可以运行了，其实不然…
正解：

6.1 创建工程目录，并进入目录

mkdir testcv
cd testcv

工程的名字根据个人喜好决定

6.2 创建cpp文件并编写测试代码

创建cpp文件：

sudo gedit test.cpp

编写代码如下：

#include "opencv2/core.hpp"
#include "opencv2/imgproc.hpp"
#include "opencv2/highgui.hpp"
#include 
using namespace cv;
using namespace std;
int main()
{
    cout << "Hello OpenCV " << CV_VERSION << endl;
    // Load image
    Mat myMat = imread("test.jpg", 1);
    // Create a window
    cvNamedWindow("Opencv Image", WINDOW_AUTOSIZE);
    // Show the image
    imshow("Opencv Image", myMat);
    // Wait 5000 ms
    waitKey(5000);
    return 0;
}

6.3 创建CMakeLists.txt文件，编辑编译代码

以下内容，直接复制粘贴的（传送门）
查看 opencv-3.4.5/samples/cpp/example_cmake 路径下的 CMakeLists.txt:

这个是 cmake 的编译文件，主要用于生成 Makefile，然后用 make 编译工程

# cmake needs this line
cmake_minimum_required(VERSION 2.8)
 
# Define project name
project(opencv_example_project)
 
# Find OpenCV, you may need to set OpenCV_DIR variable
# to the absolute path to the directory containing OpenCVConfig.cmake file
# via the command line or GUI
find_package(OpenCV REQUIRED)
 
# If the package has been found, several variables will
# be set, you can find the full list with descriptions
# in the OpenCVConfig.cmake file.
# Print some message showing some of them
message(STATUS "OpenCV library status:")
message(STATUS "    version: ${OpenCV_VERSION}")
message(STATUS "    libraries: ${OpenCV_LIBS}")
message(STATUS "    include path: ${OpenCV_INCLUDE_DIRS}")
 
if(CMAKE_VERSION VERSION_LESS "2.8.11")
  # Add OpenCV headers location to your include paths
  include_directories(${OpenCV_INCLUDE_DIRS})
endif()
 
# Declare the executable target built from your sources
add_executable(opencv_example example.cpp)
 
# Link your application with OpenCV libraries
target_link_libraries(opencv_example ${OpenCV_LIBS})

将其中的一部分按照自己的情况修改：

# cmake needs this line 要求的最低版本
cmake_minimum_required(VERSION 2.8)
# Define project name 定义工程名 
project(example_project)
# Find OpenCV, you may need to set OpenCV_DIR variable
# to the absolute path to the directory containing OpenCVConfig.cmake file
# via the command line or GUI 自动查找库
find_package(OpenCV REQUIRED)
# Declare the executable target built from your sources 声明可执行目标文件及源文件
add_executable(example example.cpp)  # 目标文件，源文件0,源文件1,...
# Link your application with OpenCV libraries 将目标文件与库链接
target_link_libraries(example ${OpenCV_LIBS})  # 目标文件，库路径

这里附上自己修改过的 CMakeLists.txt 文件：

# cmake needs this line
cmake_minimum_required(VERSION 2.8)
 
# Define project name
project(testcv)
 
# Find OpenCV, you may need to set OpenCV_DIR variable
# to the absolute path to the directory containing OpenCVConfig.cmake file
# via the command line or GUI
find_package(OpenCV REQUIRED)
 
# If the package has been found, several variables will
# be set, you can find the full list with descriptions
# in the OpenCVConfig.cmake file.
# Print some message showing some of them
message(STATUS "OpenCV library status:")
message(STATUS "    version: ${OpenCV_VERSION}")
message(STATUS "    libraries: ${OpenCV_LIBS}")
message(STATUS "    include path: ${OpenCV_INCLUDE_DIRS}")
 
if(CMAKE_VERSION VERSION_LESS "2.8.11")
  # Add OpenCV headers location to your include paths
  include_directories(${OpenCV_INCLUDE_DIRS})
endif()
 
# Declare the executable target built from your sources
add_executable(test test.cpp)
 
# Link your application with OpenCV libraries
target_link_libraries(test ${OpenCV_LIBS})

6.4 编译并运行工程

生成Makefile：

cmake .

编译工程：

make

运行可执行文件：

./test

参考：

1.OpenCV 环境搭建
2.Ubuntu 创建 OpenCV 工程