Change dpi of an image in OpenCV

Question

When I open an image in OpenCv (which may be of 300 dpi, 72 dpi etc.), the dpi of the image is automatically changed to 96 dpi. I want to variate this dpi. Please help. Thanks in advance...

#include "stdafx.h"
#include <cv.h>
#include <cxcore.h>
#include <highgui.h>
#include <iostream>
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
    IplImage *img1=cvLoadImage("input.jpg");
    cvSaveImage("output.jpg",img1);
    return(0);
}

Answer 1

OpenCV does not support meta-data mangling like this. You need to use another tool to re-set the DPI or consider incorporating libjpeg directly.

Another option is to take the OpenCV jpeg writer code and change it according to your needs.

Answer 2

You need to edit the image meta data libexif(c) or exiv2 (c++)