how to change the DPI of an image from 72DPI to 300DPI with Imagick

Question

I have an image of 72DPI and i want to change this to 300DPI for printing purposes, I want all the stuff need to be done with imagick, tried with the code following but no positive results.

<?
$im = new Imagick();
$im->setResolution(72,72);
$im->setOption('density','300x300');
$im->readImage("test.png");
header("Content-Type: image/png");
echo $im;
?>

can someone help/clarify me the usage of setoption or can some one explain hot to change DPI in either iMagick or GD

Answer 1

I think this is what you want:

I have setted resolution as pixel/inch with 300 dpi:

<?php
$im = new Imagick();
$im->setImageUnits(imagick::RESOLUTION_PIXELSPERINCH);
$im->setImageResolution(300,300);
$im->readImage("test.png");
$im->setImageFormat("png");
header("Content-Type: image/png");
echo $im;
?>

Hope this will help you!