Example

function construct($image_path)
{
    $imagick = new \Imagick(realpath($image_path));
    $imageIterator = new \ImagickPixelIterator($imagick);

    /* Loop through pixel rows */
    foreach ($imageIterator as $pixels) {
        /* Loop through the pixels in the row (columns) */
        foreach ($pixels as $column => $pixel) {
            /** @var $pixel \ImagickPixel */
            if ($column % 2) {
                /* Paint every second pixel black*/
                $pixel->setColor("rgba(0, 0, 0, 0)");
            }
        }
        /* Sync the iterator, this is important to do on each iteration */
        $imageIterator->syncIterator();
    }

    header("Content-Type: image/jpeg");
    echo $imagick;
}