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