(PECL imagick 2.0.0)
Imagick::contrastImage — Change the contrast of the image
$sharpen
   )Enhances the intensity differences between the lighter and darker elements of the image. Set sharpen to a value other than 0 to increase the image contrast otherwise the contrast is reduced.
sharpenThe sharpen value
   Returns TRUE on success.
  
Throws ImagickException on error.
Example #1 Imagick::contrastImage()
<?php
function contrastImage($imagePath, $contrastType) {
    $imagick = new \Imagick(realpath($imagePath));
    if ($contrastType != 2) {
        $imagick->contrastImage($contrastType);
    }
    header("Content-Type: image/jpg");
    echo $imagick->getImageBlob();
}
?>