(PECL imagick 2, PECL imagick 3)
Imagick::setImageCompressionQuality — Sets the image compression quality
$quality): boolSets the image compression quality.
qualityThe image compression quality as an integer
   Returns true on success.
  
Throws ImagickException on error.
Example #1 Imagick::setImageCompressionQuality()
<?php
function setImageCompressionQuality($imagePath, $quality) {
    $imagick = new \Imagick(realpath($imagePath));
    $imagick->setImageCompressionQuality($quality);
    header("Content-Type: image/jpg");
    echo $imagick->getImageBlob();
}
?>