ubuntu20.04 opencv4.2 安装笔记

参考：

https://docs.opencv.org/4.x/d7/d9f/tutorial_linux_install.html

Build with opencv_contrib

# 1. Install minimal prerequisites， libgtk2.0-dev pkg-config 用来显示图像
sudo apt update && sudo apt install -y cmake g++ wget unzip libgtk2.0-dev pkg-config

# 2. Download and unpack sources
# cd 到自己要放 opencv 的路径下，比如我们的是：/home/h/programs/cv
cd /home/h/programs/cv
sudo wget -O opencv.zip https://github.com/opencv/opencv/archive/4.2.0.zip --no-check-certificate
sudo wget -O opencv_contrib.zip https://github.com/opencv/opencv_contrib/archive/4.2.0.zip --no-check-certificate
unzip opencv.zip && unzip opencv_contrib.zip

# 3. Create build directory and switch into it
mkdir build && cd build

# 4. Configure， build 目录内
cmake -DOPENCV_EXTRA_MODULES_PATH=../opencv_contrib-4.2.0/modules ../opencv-4.2.0

# 5. build 目录内
make -j 8

# 删除压缩包
cd .. && sudo rm opencv.zip opencv_contrib.zip

编译时候报错：opencv_contrib/modules/xfeatures2d/src/boostdesc.cpp:673:20: fatal error: boostdesc_bgm.i: No such file or directory
opencv_contrib-4.2.0/modules/xfeatures2d/src/boostdesc.cpp:654:20: fatal error: boostdesc_bgm.i: 没有那个文件或目录
解决：网络问题，添加代理，然后重复 4，5 步
参考：https://www.cnblogs.com/arxive/p/11778731.html

Using OpenCV with gcc and CMake

参考：https://docs.opencv.org/4.x/db/df5/tutorial_linux_gcc_cmake.html

// DisplayImage.cpp
#include <stdio.h>
#include <opencv2/opencv.hpp>

using namespace cv;
int main(int argc, char** argv )
{
	if ( argc != 2 )
	{
		printf("usage: DisplayImage.out <Image_Path>\n");
		return -1;
	}
	Mat image;
	image = imread( argv[1], IMREAD_COLOR );
	if ( !image.data )
	{
		printf("No image data \n");
		return -1;
	}
	namedWindow("Display Image", WINDOW_AUTOSIZE );
	imshow("Display Image", image);
	waitKey(0);
	return 0;
}

CMakeLists.txt:

cmake_minimum_required(VERSION 2.8)
set(OpenCV_DIR /home/h/programs/cv/build)
project( DisplayImage )
find_package( OpenCV REQUIRED )
include_directories( ${OpenCV_INCLUDE_DIRS} )
add_executable( DisplayImage DisplayImage.cpp )
target_link_libraries( DisplayImage ${OpenCV_LIBS} )

Create build directory and switch into it

mkdir build && cd build

目录：

.
├── build
├── CMakeLists.txt
└── DisplayImage.cpp

cmake ..

报错： By not providing “FindOpenCV.cmake” in CMAKE_MODULE_PATH this project has
asked CMake to find a package configuration file provided by “OpenCV”, but
CMake did not find one.
Could not find a package configuration file provided by “OpenCV” with any
of the following names:
OpenCVConfig.cmake
opencv-config.cmake
Add the installation prefix of “OpenCV” to CMAKE_PREFIX_PATH or set
“OpenCV_DIR” to a directory containing one of the above files. If “OpenCV”
provides a separate development package or SDK, be sure it has been
installed.

解决：

方式1：

# CMakeLists.txt:
set(OpenCV_DIR /home/h/programs/cv/build)

方式2：

cmake -DOpenCV_DIR=/home/h/programs/cv/build  ..

然后：

# 在build 文件夹下
make
./DisplayImage lena.jpg

报错：

Gtk-Message: 23:48:54.655: Failed to load module “canberra-gtk-module”

解决：

sudo apt-get install libcanberra-gtk-module

其他：

为python3构建opencv：https://stackoverflow.com/a/39409570