(PECL imagick 2.0.0)
Imagick::setImageResolution — Sets the image resolution
$x_resolution
   , float $y_resolution
   )Sets the image resolution.
x_resolution
y_resolution
   Returns TRUE on success.
  
Throws ImagickException on error.
Example #1 Imagick::setImageResolution()
<?php
function setImageResolution($imagePath) {
    $imagick = new \Imagick(realpath($imagePath));
    $imagick->setImageResolution(50, 50);
    
    header("Content-Type: image/jpg");
    echo $imagick->getImageBlob();
}
?>