ColorThief\ColorThief::naturalOrder PHP Method

    public static function naturalOrder($a, $b)
    {
        return $a < $b ? -1 : ($a > $b ? 1 : 0);
    }

 private static function quantize($pixels, $maxcolors)
 {
     // short-circuit
     if (!count($pixels) || $maxcolors < 2 || $maxcolors > 256) {
         // echo 'wrong number of maxcolors'."\n";
         return false;
     }
     $histo = static::getHisto($pixels);
     // check that we aren't below maxcolors already
     //if (count($histo) <= $maxcolors) {
     // XXX: generate the new colors from the histo and return
     //}
     $vbox = static::vboxFromPixels($pixels, $histo);
     $pq = new PQueue(function ($a, $b) {
         return ColorThief::naturalOrder($a->count(), $b->count());
     });
     $pq->push($vbox);
     // first set of colors, sorted by population
     static::quantizeIter($pq, self::FRACT_BY_POPULATIONS * $maxcolors, $histo);
     // Re-sort by the product of pixel occupancy times the size in color space.
     $pq2 = new PQueue(function ($a, $b) {
         return ColorThief::naturalOrder($a->count() * $a->volume(), $b->count() * $b->volume());
     });
     for ($i = $pq->size(); $i > 0; $i--) {
         $pq2->push($pq->pop());
     }
     // next set - generate the median cuts using the (npix * vol) sorting.
     static::quantizeIter($pq2, $maxcolors - $pq2->size(), $histo);
     // calculate the actual colors
     $cmap = new CMap();
     for ($i = $pq2->size(); $i > 0; $i--) {
         $cmap->push($pq2->pop());
     }
     return $cmap;
 }