gistfile1.php

<?php

$img = new Imagick();
$img->readImage('car.jpg');

$draw = new ImagickDraw();

/*
 * Contrast enhancement
 *
 * Contrast of each image is enhanced through histogram equalization technique. This method usually increases the
 * global contrast of many images, especially when the usable data of the image is represented by close contrast values.
 *
 * http://en.wikipedia.org/wiki/Histogram_equalization
*/

$img->equalizeImage();

/*
 * Median filtering
 *
 * Replaces the gray value of a pixel by the median of the
 * gray values of its neighbors. We have used 3 × 3 masks to get eight neighbors of a pixel and their
 * corresponding gray values. This operation removes salt-and-peeper noise from the image.
 */

$img->medianFilterImage(3);


// Convert to 8-bit gray scale
$img->quantizeimage(256, Imagick::COLORSPACE_GRAY, 8, true, true);

// 3x3 gx Sobel mask for vertical edge detection
$gy = array(
    array(-1, 0, 1),
    array(-2, 0, 2),
    array(-1, 0, 1),
);


// edge detection using Sobel mask
$it = $img->getPixelIterator();
foreach ($it as $y => $pixels) {
    /** @var $pixel \ImagickPixel */
    foreach ($pixels as $x => $pixel) {

        $rawColour = $pixel->getcolor();

        $sumY = 0;

        for ($i = -1; $i <= 1; $i++) {
            for ($j = -1; $j <= 1; $j++) {
                $rawColour = $img->getimagepixelcolor($x + $i, $y + $j)->getcolor();

                $r = $rawColour['r'];
                $g = $rawColour['g'];
                $b = $rawColour['b'];
                $rgb = ($r + $g + $b);

                $sumY += ($rgb * $gy[$i+1][$j+1]) / 4;
            }
        }

        // combine gradient approximations to give the gradient magnitude
        $gray = abs(sqrt($sumY * $sumY));
        if ($gray > 255) {
            $gray = 255;
        }

        $pix  = new ImagickPixel("rgb($gray, $gray, $gray)");
        $draw->setFillColor($pix);
        $draw->point($x, $y);
    }

    $it->syncIterator();

    echo "computed column {$y}\n";
}

$img->drawImage($draw);
$img->writeimage('temp.jpg');

fwiw, this is only an experiment, I do not advice to use this code in production, PHP is not the right tool for this :)