程序testOpenCV.cpp：读取图像，显示图像，滤波，降采样，存图像，读像素值

#include<iostream>
#include<opencv2/opencv.hpp>
using namespace std;
int main(int argc,char **argv)
{
	if(argc==1)
	{
		cout<<"usage: ./testOpenCV <Image_Path>\n";
		return 1;
	}

	cv::Mat image_raw;
	//读取图像
	image_raw=cv::imread(argv[1],1); //1：彩色图     0：灰度图     -1：带深度的图

	if(image_raw.empty())
	{
		cout<<"No image data \n";
		return 1;
	}
    //创建个显示窗口
	cv::namedWindow("window0",cv::WINDOW_AUTOSIZE);
	//显示图像
	cv::imshow("window0",image_raw);

	cv::Mat image_gray;
	cv::cvtColor(image_raw,image_gray,CV_BGR2GRAY);//RGB图转灰度图
	cv::namedWindow("window1",cv::WINDOW_AUTOSIZE);
	cv::imshow("window1",image_gray);

	cv::Mat image_pyrDown1;
	cv::pyrDown(image_gray,image_pyrDown1);//滤波和降采样（大小变为原来1/2）
	cv::namedWindow("window2",cv::WINDOW_AUTOSIZE);
	cv::imshow("window2",image_pyrDown1);

	cv::Mat image_pyrDown2;
	cv::pyrDown(image_pyrDown1,image_pyrDown2);//再次滤波和降采样
	cv::namedWindow("window3",cv::WINDOW_AUTOSIZE);
	cv::imshow("window3",image_pyrDown2);

	cv::imwrite("gray_pyrdown_image.jpg",image_pyrDown2);  //写，存储图像

	cv::Mat image_canny;
	cv::Canny(image_pyrDown2,image_canny,10,100,3,true);//Canny边缘检测
	cv::namedWindow("window4",cv::WINDOW_AUTOSIZE);
	cv::imshow("window4",image_canny);

	cv::imwrite("pyrdown_canny_image.jpg",image_canny);  //写，存储图像

	//读取像素值（RGB图）
	int length=image_raw.cols-1;//  .cols，.rows 访问图像的列数（长）和行数（高）
	int high=image_raw.rows-1;
	cout<<"length = "<<length<<endl<<"high = "<<high<<endl;
	for (int i=0;i<4;i++)
	{
		for(int j=0;j<3;j++)
		{
			cv::Vec3b pixel=image_raw.at<cv::Vec3b>(i,j); //(列，行)
			cout<<"pixel["<<i<<","<<j<<"]"<<" value (B,G,R): ("<<(int)pixel[0]<<" , "<<(int)pixel[1]<<" , "<<(int)pixel[2]<<" )"<<endl;
		}
	}

	//读取像素值（灰度图）
	for (int i=0; i<4; i++)
	{
		for(int j=0; j<3; j++)
		{
			uchar pixel=image_gray.at<uchar>(i,j);
			cout<<"pixel["<<i<<","<<j<<"]"<<" value (gray): ("<<(short)pixel<<")"<<endl;
		}
	}



	cv::waitKey(0);

	return 0;
}

CMakeLists.txt文件

cmake_minimum_required(VERSION 3.0)
project(testOpenCV)
find_package(OpenCV 3  REQUIRED)

message("OpenCV version::::${OpenCV_VERSION}")
message("OpenCV_INCLUDE_DIRS:::::${OpenCV_INCLUDE_DIRS}")
message("OpenCV_LIBS::::::::${OpenCV_LIBS}")

set(EXECUTABLE_OUTPUT_PATH ${PROJECT_SOURCE_DIR}/bin)

include_directories(${OpenCV_INCLUDE_DIRS})

add_executable(${PROJECT_NAME} src/testOpenCV.cpp)

target_link_libraries(${PROJECT_NAME} ${OpenCV_LIBS})