(PECL imagick 2.0.0)
Imagick::charcoalImage — Simulates a charcoal drawing
$radius
   , float $sigma
   )Simulates a charcoal drawing.
radiusThe radius of the Gaussian, in pixels, not counting the center pixel
sigmaThe standard deviation of the Gaussian, in pixels
   Returns TRUE on success.
  
Example #1 Imagick::charcoalImage()
<?php
function charcoalImage($imagePath, $radius, $sigma) {
    $imagick = new \Imagick(realpath($imagePath));
    $imagick->charcoalImage($radius, $sigma);
    header("Content-Type: image/jpg");
    echo $imagick->getImageBlob();
}
?>