OpenCV中pyrUp()和pyrDown()函数使用

cmakelists:

cmake_minimum_required(VERSION 3.7)project(pyrUp_and_pyrDown)set(CMAKE_CXX_STANDARD 11)find_package(OpenCV REQUIRED)include_directories(${OpenCV_DIRS})set(SOURCE_FILES main.cpp)add_executable(pyrUp_and_pyrDown ${SOURCE_FILES})target_link_libraries(pyrUp_and_pyrDown ${OpenCV_LIBS})

程序：

#include <iostream>#include <opencv2/core/core.hpp>#include <opencv2/highgui/highgui.hpp>#include <opencv2/imgproc/imgproc.hpp>using namespace std;using namespace cv;int main(){    Mat src_image = imread("ubuntu.png");    Mat tmp_image, dst_image1, dst_image2;    tmp_image = src_image;    imshow("原始图片", src_image);    //看一下函数原型    //参数：源图像，目标图像    //这里的const Size& dstsize = Size()是有默认值的，不像resize()没有默认值。默认值是放大或缩小一倍    //第三个边界类型一般不管它，用默认值就好/*    CV_EXPORTS_W void pyrUp( InputArray src, OutputArray dst,                             const Size& dstsize = Size(),                             int borderType = BORDER_DEFAULT );*//*    CV_EXPORTS_W void pyrDown( InputArray src, OutputArray dst,                               const Size& dstsize = Size(),                               int borderType = BORDER_DEFAULT );*/    pyrUp(tmp_image, dst_image1, Size(tmp_image.cols*2, tmp_image.rows*2));    pyrDown(tmp_image, dst_image2, Size(tmp_image.cols/2, tmp_image.rows/2));    imshow("pyrUp放大图像", dst_image1);    imshow("pyrDown缩小图像", dst_image2);    waitKey(0);    return 0;}

这里注意一下，pyrup和pyrdown函数只能固定对图像进行长宽二倍或半倍的缩小和放大，不能是其他大小，也就是pyrDown(）中的Size(tmp_image.cols/2, tmp_image.rows/2)必须是这个大小，换成其他的会报错，同理pyrUp()也是一样，必须是*2。如果想多次放缩，可以用循环多次调用。
例如像这样：

int main(){    Mat src_image=imread("open2.JPG");    Mat src_image_gray;    cvtColor( src_image, src_image_gray, CV_BGR2GRAY );    //imshow("原始图：", src_image);    Mat tmp_image, imagel;    tmp_image = src_image_gray;    for (int i = 0; i < 2; ++i)    {        pyrDown(tmp_image, imagel, Size(tmp_image.cols/2, tmp_image.rows/2));        tmp_image=imagel;    }    cout<<imagel.cols<<"*"<<imagel.rows<<endl;    imshow("降低分辨率后：", imagel);    std::vector<KeyPoint> keypoints_1;    Ptr<ORB> orb = ORB::create();    orb->detect(imagel,keypoints_1);    cout<<keypoints_1.size()<<endl;    Mat imagel_with_keypoints;    drawKeypoints(imagel, keypoints_1, imagel_with_keypoints, Scalar::all(-1), DrawMatchesFlags::DEFAULT);    imshow("关键点图：", imagel_with_keypoints);    waitKey(0);    return 0;}