OpenCV 中Resize 和 cvPydown的使用

載入一幅圖像分別使用cvResize() 和 cvPyrDown()進行圖片的三次縮放，比較結果；

#include <iostream>
#include <opencv2/opencv.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/core/core.hpp>
#include <stdio.h>
#include <cstdlib>

using namespace std;
using namespace cv;

IplImage * doPryDown(IplImage * in,int filter=CV_GAUSSIAN_5x5)
{
    //assert(in->width%2==0 && in->height%2==0);
    IplImage * out=cvCreateImage(cvSize(in->width/2,in->height/2),in->depth,in->nChannels);
    cvPyrDown(in,out,CV_GAUSSIAN_5x5);//filter=7 目前只支持CV_GAUSSIAN_5x5
    return (out);
}

int main(int argc, const char * argv[]) {
    /*1.載入圖像，並轉化爲灰度圖像*/
    const char filename[] = "/Users/linwang/Downloads/30.png";
    IplImage * Img = cvLoadImage(filename,CV_LOAD_IMAGE_GRAYSCALE);
    cvShowImage("Gray-Lena", Img);
    
    /*2. 將這幅圖像縮小三次，並顯示結果*/
    double fscale = 0.5;
    CvSize czSize;
    IplImage * dst =  0;
    for(int i = 0;i<3;i++)
    {
        czSize.width  = Img->width  * pow(fscale, i+1);
        czSize.height = Img->height * pow(fscale, i+1);
        dst =  cvCreateImage(czSize, Img->depth, Img->nChannels);
        cvResize(Img, dst);
    }
    cvShowImage("Gray-Lena", dst);
    
    
    /*3.利用cvPryDown（）函數在原始圖像上進行三次降採樣操作*/
    int count = 3;
    while (count>0) {
        IplImage * out = doPryDown(Img);
        Img = cvCloneImage(out);
        count--;
    }
    cvShowImage("PyrDown", Img);
    cvWaitKey(0);
    return 1;
}

Resize()：將圖像精確的轉換爲目標圖像的尺寸，需要用到一些插值方法；

cvPyrdown會失真。