(PECL imagick 2.0.0)
Imagick::sharpenImage — Sharpens an image
$radius
   , float $sigma
   [, int $channel = Imagick::CHANNEL_ALL
  ] )Sharpens an image. We convolve the image with a Gaussian operator of the given radius and standard deviation (sigma). For reasonable results, the radius should be larger than sigma. Use a radius of 0 and Imagick::sharpenImage() selects a suitable radius for you.
radius
sigma
channel
   Returns TRUE on success.
  
Example #1 Imagick::sharpenImage()
<?php
function sharpenImage($imagePath, $radius, $sigma, $channel) {
    $imagick = new \Imagick(realpath($imagePath));
    $imagick->sharpenimage($radius, $sigma, $channel);
    header("Content-Type: image/jpg");
    echo $imagick->getImageBlob();
}
?>