#include <iostream>
#include <opencv2\opencv.hpp> 
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include "stdio.h"
using namespace std;
using namespace cv;


int main(int argc,char *argv[])
{
 Mat img1=imread("1.JPG");
         Mat img2;
//将原图像变为40×30
         resize(img1,img2,Size(40,30),0,0,CV_INTER_LINEAR);
         namedWindow("WindowOrg");
         namedWindow("WindowNew");
         imshow("WindowOrg",img1);
         imshow("WindowNew",img2);
         imwrite( "改变后.JPG", img2);
         waitKey();
}

opencv2改变图像像素大小到指定像素并保存改变后的图像