ubuntu20.04+opencv4.5.1

我的环境可以进行科学上网,编译的时候就不会出现各种下载错误~

1.安装依赖

sudo apt-get install libjpeg-dev libpng-dev libtiff5-dev libjasper-dev libdc1394-22-dev libeigen3-dev libtheora-dev libvorbis-dev libxvidcore-dev libx264-dev sphinx-common libtbb-dev yasm libfaac-dev libopencore-amrnb-dev libopencore-amrwb-dev libopenexr-dev libgstreamer-plugins-base1.0-dev libavutil-dev libavfilter-dev libavresample-dev
sudo apt-get install build-essential cmake git libgtk2.0-dev libgtk-3-dev pkg-config libavcodec-dev libavformat-dev libswscale-dev

如果提示找不到libfaac-dev软件包

sudo apt-add-repository "deb http://us.archive.ubuntu.com/ubuntu trusty main multiverse"
sudo apt update
sudo apt install libjasper1 libjasper-dev

如果提示找不到libjasper-dev软件包

sudo apt-add-repository "deb http://security.ubuntu.com/ubuntu xenial-security main"
sudo apt update
sudo apt install libjasper1 libjasper-dev

2. 下载源码

cd ~/ #my_working_directory是你保存opencv和opencv_contrib的文件夹
git clone https://github.com/opencv/opencv.git
git clone https://github.com/opencv/opencv_contrib.git
mv  opencv_contrib/  opencv/	#将opencv_contrib移动到opencv目录里

3.编译

cd opencv
mkdir build
cd build
cmake -D CMAKE_BUILD_TYPE=Release -D CMAKE_INSTALL_PREFIX=/usr/local -D OPENCV_EXTRA_MODULES_PATH=../opencv_contrib/modules -D OPENCV_GENERATE_PKGCONFIG=ON ..

cmake参数解释：
CMAKE_INSTALL_PREFIX=/usr/local 该路径是opencv的默认安装目录，不建议修改。
OPENCV_EXTRA_MODULES_PATH=…/opencv_contrib/modules 该路径是opencv_contrib所在的文件夹。层次关系：

	opencv
		opencv_contrib
		build

OPENCV_GENERATE_PKGCONFIG=ON 表示会生成opencv.pc文件，要使之后添加的环境变量有效，就必须得有这个文件，很重要。

执行

sudo make -j4 #时间较长
sudo make install
sudo ldconfig  #生效,可以第5步测试可不可以,不可以就继续进行第四步

4.添加路径

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

末尾添加（可能空的）

/usr/local/lib

生效

sudo ldconfig

sudo gedit /etc/ld.so.conf

末尾添加（若已经有了第一行就直接添加第二行）

include /etc/ld.so.conf.d/*.conf
include /usr/local/lib

生效

sudo ldconfig

sudo gedit /etc/bash.bashrc

末尾添加

PKG_CONFIG_PATH=$PKG_CONFIG_PATH:/usr/local/lib/pkgconfig
export PKG_CONFIG_PATH

生效

source /etc/bash.bashrc

5.测试

cd ../samples/cpp/example_cmake
cmake .
make
./opencv_example

或（我采用这种方式）

pkg-config opencv --modversion		#opencv3
pkg-config --modversion opencv4   #opencv4

显示出版本号就说明安装完毕。
出现错误

Package opencv was not found in the pkg-config search path.
Perhaps you should add the directory containing `opencv.pc'
to the PKG_CONFIG_PATH environment variable
No package 'opencv' found

意思是它找不到opencv.pc这个文件，实际上该文件在/usr/local/lib/pkgconfig目录下，我在该目录下发现文件名字是opencv4.pc，复制了一个名为opencv.pc，然后解决了。

参考1：https://blog.csdn.net/qq_45488453/article/details/110289423
参考2：https://blog.csdn.net/qq_41169447/article/details/109139884