1.什麼是OpenCV？
OpenCV是一個基於BSD許可（開源）發行的跨平臺計算機視覺庫，可以運行在Linux、Windows、Android和Mac OS操作系統上。它輕量級而且高效——由一系列 C 函數和少量 C++ 類構成，同時提供了Python、Ruby、MATLAB等語言的接口，實現了圖像處理和計算機視覺方面的很多通用算法。
OpenCV用C++語言編寫，它的主要接口也是C++語言，但是依然保留了大量的C語言接口。該庫也有大量的Python、Java and MATLAB/OCTAVE（版本2.5）的接口。這些語言的API接口函數可以通過在線文檔獲得。如今也提供對於C#、Ch、Ruby,GO的支持。
——摘自百度
2.準備工作
首先,要更新 Ubuntu 的庫
sudo apt-get update
sudo apt-get upgrade
然後安裝一些 OpenCV 會用的庫（這一步一定要認真做，否則後面會出現各種莫名其妙的錯誤！！！）
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
在這一步中可能會遇到報錯：
沒有可用的軟件包 libtiff4-dev，但是它被其它的軟件包引用了。
這可能意味着這個缺失的軟件包可能已被廢棄，
或者只能在其他發佈源中找到
然而下列軟件包會取代它：
libtiff5-dev:i386 libtiff5-dev
解決方案是（其實是隨便選了第二個…）：
sudo apt-get install libtiff5-dev
尤其是 libgtk2.0-dev 和 pkg-config 這兩個庫，否則在後面運行例程時會報錯：
terminate called after throwing an instance of ‘cv::Exception’
what(): OpenCV(3.4.5) /home/cxy/文檔/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’
如果忘記了裝上面的某個庫，在補裝了以後要重新執行第4部分中的內容纔可以正常編譯工程。
3.OpenCV 下載
直接從官網提供的鏈接下載就行：OpenCV source download
下載解壓後放在合適的位置，進入解壓目錄，進行如下操作，爲OpenCV的編譯作準備：
mkdir release
cd release
4.編譯 OpenCV
首先，設置 cmake 編譯參數：
sudo cmake …
然後開始編譯 OpenCV：
sudo make
sudo make install
注：編譯第一步可能耗時比較久，建議找點其他事做！
5.配置環境變量
網上可以查到很多種方法，這裏提供一種親測可行的方法，僅供參考：
sudo gedit /etc/ld.so.conf.d/opencv.conf
在文件 opencv.conf 內的末尾添加 “/usr/local/lib” 並保存；
更新系統的共享鏈接庫：
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環境搭建完畢（大功告成.jpg）。
6.編寫測試項目
一開始以爲配好環境，寫一個 cpp 文件就可以運行了，其實不然…
正解：
6.1 創建工程目錄，並進入目錄
mkdir testcv
cd testcv
工程的名字根據個人喜好決定
6.2 創建cpp文件並編寫測試代碼
創建cpp文件：
sudo gedit test.cpp
編寫代碼如下：
#include "opencv2/core.hpp"
#include "opencv2/imgproc.hpp"
#include "opencv2/highgui.hpp"
#include <iostream>
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 創建CMakeLists.txt文件，編輯編譯代碼
以下內容，直接複製粘貼的（傳送門）
查看 opencv-3.4.5/samples/cpp/example_cmake 路徑下的 CMakeLists.txt:
這個是 cmake 的編譯文件，主要用於生成 Makefile，然後用 make 編譯工程
# 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})
將其中的一部分按照自己的情況修改：
# cmake needs this line 要求的最低版本
cmake_minimum_required(VERSION 2.8)
# Define project name 定義工程名
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 自動查找庫
find_package(OpenCV REQUIRED)
# Declare the executable target built from your sources 聲明可執行目標文件及源文件
add_executable(example example.cpp) # 目標文件，源文件0,源文件1,...
# Link your application with OpenCV libraries 將目標文件與庫鏈接
target_link_libraries(example ${OpenCV_LIBS}) # 目標文件，庫路徑
這裏附上自己修改過的 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 編譯並運行工程
生成Makefile：
cmake .
編譯工程：
make
運行可執行文件：
./test
