(PECL imagick 0.9.10-0.9.9)
Imagick::setCompressionQuality — Sets the object's default compression quality
$quality
   ) : boolSets the object's default compression quality.
This method only works for new images e.g. those created through Imagick::newPseudoImage. For existing images you should use Imagick::setImageCompressionQuality().
quality
   成功时返回 TRUE。
  
Example #1 Imagick::setCompressionQuality()
<?php
function setCompressionQuality($imagePath, $quality) {
    $backgroundImagick = new \Imagick(realpath($imagePath));
    $imagick = new \Imagick();
    $imagick->setCompressionQuality($quality);
    $imagick->newPseudoImage(
        $backgroundImagick->getImageWidth(),
        $backgroundImagick->getImageHeight(),
        'canvas:white'
    );
    $imagick->compositeImage(
        $backgroundImagick,
        \Imagick::COMPOSITE_ATOP,
        0,
        0
    );
    
    $imagick->setFormat("jpg");    
    header("Content-Type: image/jpg");
    echo $imagick->getImageBlob();
}
?>