Как можно ускорить код php?

<?php
class HalFaceRec {
    protected $detection_data;
    protected $img;
    protected $face;
    private $reduced_img;
    
    public function __construct() {
        $this->detection_data = unserialize(file_get_contents('detection.dat'));
    }
    
    public function getImgStats($img) {
        $imgw = imagesx($img);
        $imgh = imagesy($img);
        $iis = $this->computeII($img,$imgw,$imgh);
        return [
            'width'=>$imgw,
            'height'=>$imgh,
            'ii'=>$iis['ii'],
            'ii2'=>$iis['ii2']
        ];
    }
    
    public function computeII($img,$imgw,$imgh) {
        $ii_w = $imgw+1;
        $ii_h = $imgh+1;
        $ii = array();
        $ii2 = array();

        for ($i=0; $i<$ii_w; $i++) {
            $ii[$i] = 0;
            $ii2[$i] = 0;
        }

        for ($i=1; $i<$ii_h-1; $i++) {
            $ii[$i*$ii_w] = 0;
            $ii2[$i*$ii_w] = 0;
            $rowsum = 0;
            $rowsum2 = 0;
            for ($j=1; $j<$ii_w-1; $j++) {
                $rgb = ImageColorAt($img, $j, $i);
                $red = ($rgb >> 16) & 0xFF;
                $green = ($rgb >> 8) & 0xFF;
                $blue = $rgb & 0xFF;
                $grey = (0.2989*$red + 0.587*$green + 0.114*$blue)>>0;  // this is what matlab uses
                $rowsum += $grey;
                $rowsum2 += $grey*$grey;

                $ii_above = ($i-1)*$ii_w + $j;
                $ii_this = $i*$ii_w + $j;

                $ii[$ii_this] = $ii[$ii_above] + $rowsum;
                $ii2[$ii_this] = $ii2[$ii_above] + $rowsum2;
            }
        }
        return ['ii'=>$ii, 'ii2' => $ii2];
    }
    
    public function detectOnSubImage($x,$y,$scale,$ii,$ii2,$w,$iiw,$inv_area,$count_data) {
        $mean  = ($ii[($y+$w)*$iiw + $x + $w] + $ii[$y*$iiw+$x] - $ii[($y+$w)*$iiw+$x] - $ii[$y*$iiw+$x+$w])*$inv_area;

        $vnorm = ($ii2[($y+$w)*$iiw + $x + $w]
                  + $ii2[$y*$iiw+$x]
                  - $ii2[($y+$w)*$iiw+$x]
                  - $ii2[$y*$iiw+$x+$w])*$inv_area - ($mean*$mean);

        $vnorm = $vnorm > 1 ? sqrt($vnorm) : 1;

        for ($i_stage = 0; $i_stage < $count_data; $i_stage++) {
            $stage = $this->detection_data[$i_stage];
            $trees = $stage[0];

            $stage_thresh = $stage[1];
            $stage_sum = 0;

            $count_trees = count($trees);

            for ($i_tree = 0; $i_tree < $count_trees; $i_tree++) {
                $tree = $trees[$i_tree];
                $current_node = $tree[0];
                $tree_sum = 0;
                while ($current_node != null) {
                    $vals = $current_node[0];
                    $node_thresh = $vals[0];
                    $leftval = $vals[1];
                    $rightval = $vals[2];
                    $leftidx = $vals[3];
                    $rightidx = $vals[4];
                    $rects = $current_node[1];

                    $rect_sum = 0;
                    $count_rects = count($rects);

                    for ($i_rect = 0; $i_rect < $count_rects; $i_rect++) {
                        $s = $scale;
                        $rect = $rects[$i_rect];
                        $rx = ($rect[0]*$s+$x)>>0;
                        $ry = ($rect[1]*$s+$y)>>0;
                        $rw = ($rect[2]*$s)>>0;
                        $rh = ($rect[3]*$s)>>0;
                        $wt = $rect[4];

                        $r_sum = ($ii[($ry+$rh)*$iiw + $rx + $rw]
                                  + $ii[$ry*$iiw+$rx]
                                  - $ii[($ry+$rh)*$iiw+$rx]
                                  - $ii[$ry*$iiw+$rx+$rw])*$wt;

                        $rect_sum += $r_sum;
                    }

                    $rect_sum *= $inv_area;

                    $current_node = null;

                    if ($rect_sum >= $node_thresh*$vnorm) {

                        if ($rightidx == -1) {

                            $tree_sum = $rightval;

                        } else {

                            $current_node = $tree[$rightidx];

                        }

                    } else {

                        if ($leftidx == -1) {

                            $tree_sum = $leftval;

                        } else {

                            $current_node = $tree[$leftidx];
                        }
                    }
                }

                $stage_sum += $tree_sum;
            }
            if ($stage_sum < $stage_thresh) {
                return false;
            }
        }
        return true;
    }
    
    public function detectGreedyBigToSmall($ii,$ii2,$width,$height,$s_w,$s_h) {
        $start_scale = $s_h < $s_w ? $s_h : $s_w;
        $scale_update = 1 / 1.2;
        $count_data = count($this->detection_data);
        $out = [];
        for ($scale = $start_scale; $scale > 1; $scale *= $scale_update) {
            $w = (20*$scale) >> 0;
            $endx = $width - $w - 1;
            $endy = $height - $w - 1;
            $step = max($scale, 2) >> 0;
            $inv_area = 1 / ($w*$w);
            for ($y = 0; $y < $endy; $y += $step) {
                for ($x = 0; $x < $endx; $x += $step) {
                    $passed = $this->detectOnSubImage($x, $y, $scale, $ii, $ii2, $w, $width+1, $inv_area,$count_data);
                    if ($passed) {
                        $out[] = ['x'=>$x, 'y'=>$y, 'w'=>$w];
                    }
                } // end x
            } // end y
        }  // end scale
        return $out;
    }
    
    public function faceDetect($img) {
        if (is_resource($img)) {
            $this->img = $img;
        } else if (is_file($img)) {
            $ex = explode('.',$img);
            $ex = $ex[count($ex)-1];
            if ($ex == 'png') {
                $this->img = imagecreatefrompng($img);
            } else if ($ex == 'bmp') {
                $this->img = imagecreatefrombmp($img);
            } else {
                $this->img = imagecreatefromjpeg($img);
            }
        } else if (is_string($img)) {
            $this->img = imagecreatefromstring($img);
        } else {
            throw new Exception("Can't load your image");
        }
        
        $imgw = imagesx($this->img);
        $imgh = imagesy($this->img);
        
        $diffw = 320 - $imgw;
        $diffh = 240 - $imgh;
        if ($diffw > $diffh) {
            $ratio = $imgw / 320;
        } else {
            $ratio = $imgh / 240;
        }
        
        if ($ratio != 0) {
            $this->reduced_img = imagecreatetruecolor($imgw/$ratio,$imgh/$ratio);
            imagecopyresampled(
                $this->reduced_img,
                $this->img,
                0,
                0,
                0,
                0,
                $imgw/$ratio,
                $imgh/$ratio,
                $imgw,
                $imgh
            );
            
            $stats = $this->getImgStats($this->reduced_img);
            $this->face = $this->detectGreedyBigToSmall(
                $stats['ii'],
                $stats['ii2'],
                $stats['width'],
                $stats['height'],
                $stats['width']/20,
                $stats['height']/20
            );
            
            if (count($this->face) > 0) {
                for ($i = 0; $i < count($this->face); $i++) {
                    $this->face[$i]['x'] *= $ratio;
                    $this->face[$i]['y'] *= $ratio;
                    $this->face[$i]['w'] *= $ratio;
                }
            }
            return $this->face;
        } else {
            $stats = $this->getImgStats($this->img);
            $this->face = $this->detectGreedyBigToSmall(
                $stats['ii'],
                $stats['ii2'],
                $stats['width'],
                $stats['height'],
                $stats['width']/20,
                $stats['height']/20
            );
            return $this->face;
        }
    }
    
    public function draw($img,$result) {
        $color = imagecolorallocate($img,255,0,0);
        foreach ($result as $res) {
            imagerectangle(
                $img,
                $res['x'],
                $res['y'],
                $res['x']+$res['w'],
                $res['y']+$res['w'],
                $color
            );
        }
        return $img;
    }
    
    public function cropFace($img,$result) {
        $res = $result[0];
        $thumb = imagecreatetruecolor($res['w'],$res['w']);
        imagecopy($thumb,$img,0,0,$res['x'],$res['y'],$res['w'],$res['w']);
        return $thumb;
    }
}

$facerec = new HalFaceRec();
if (!empty($_GET['req']) and !empty($_FILES['img'])) {
    $req = $_GET['req'];
    if ($req == 'detectAndDraw') {
        $img = imagecreatefromjpeg($_FILES['img']['tmp_name']);
        header('Content-Type: image/jpeg');
        imagejpeg($facerec->draw($img,$facerec->faceDetect($img)));
    } else if ($req == 'detectAndCrop') {
        $img = imagecreatefromjpeg($_FILES['img']['tmp_name']);
        header('Content-Type: image/jpeg');
        imagejpeg($facerec->cropFace($img,$facerec->faceDetect($img)));
    }
}
?>