FaceDetector.php

<?php
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
//
// @Author Karthik Tharavaad
//         karthik_tharavaad@yahoo.com
// @Contributor Maurice Svay
//              maurice@svay.Com

class Face_Detector {

    protected $detection_data;
    protected $canvas;
    protected $faces;
    protected $ratio;
    public static $offset;
    private $reduced_canvas;

    public function __construct($detection_file = 'detection.dat') {
        if (is_file($detection_file)) {
            $this->detection_data = unserialize(file_get_contents($detection_file));
        } else {
            throw new Exception("Couldn't load detection data");
        }
    }

    public function face_detect(&$file) {
        if (is_resource($file)) {
            $this->canvas = $file;
        }
        elseif (is_file($file)) {
            $info = getimagesize($file);
            if( $info[2] == IMAGETYPE_JPEG ) {
                $this->canvas = imagecreatefromjpeg($file);
            }
            elseif( $info[2] == IMAGETYPE_GIF ) {
                $this->canvas = imagecreatefromgif($file);
            }
            elseif( $info[2] == IMAGETYPE_PNG ) {
                $this->canvas = imagecreatefrompng($file);
            }
            else {
                throw new Exception("Unknown file format: .".$info[2].", ".$file);
            }
        }
        else {
            throw new Exception("Can not load $file");
        }

        $im_width = imagesx($this->canvas);
        $im_height = imagesy($this->canvas);

        self::$offset = 10;

        //Resample before detection?
        $this->ratio = 0;
        $diff_width = 320 - $im_width;
        $diff_height = 240 - $im_height;
        if ($diff_width > $diff_height) {
            $this->ratio = $im_width / 320;
        } else {
            $this->ratio = $im_height / 240;
        }

        if ($this->ratio != 0) {
            $this->reduced_canvas = imagecreatetruecolor($im_width / $this->ratio, $im_height / $this->ratio);
            imagecopyresampled($this->reduced_canvas, $this->canvas, 0, 0, 0, 0, $im_width / $this->ratio, $im_height / $this->ratio, $im_width, $im_height);
        }

        // find faces
        $stats = $this->get_img_stats($this->ratio ? $this->reduced_canvas : $this->canvas);
        $this->do_detect_greedy_big_to_small($stats['ii'], $stats['ii2'], $stats['width'], $stats['height']);

        foreach( $this->faces as &$face ) {
            if ($this->ratio && $face['w'] > 0) {
                $face['x'] = (int)round( $face['x'] * $this->ratio );
                $face['y'] = (int)round( $face['y'] * $this->ratio );
                $face['w'] = (int)round( $face['w'] * $this->ratio );
            }
        }

        return ($this->faces[0]['w'] > 0);
    }


    public function toJpeg($index = 0) {
        $color = imagecolorallocate($this->canvas, 255, 0, 0); //red
        imagerectangle($this->canvas, $this->faces[$index]['x'], $this->faces[$index]['y'], $this->faces[$index]['x']+$this->faces[$index]['w'], $this->faces[$index]['y']+ $this->faces[$index]['w'], $color);
        header('Content-type: image/jpeg');
        imagejpeg($this->canvas);
    }

    public function toJson() {
        return json_encode($this->faces);
    }

    public function getFaces() {
        return $this->faces;
    }

    protected function get_img_stats($canvas){
        $image_width = imagesx($canvas);
        $image_height = imagesy($canvas);
        $iis =  $this->compute_ii($canvas, $image_width, $image_height);
        return array(
            'width' => $image_width,
            'height' => $image_height,
            'ii' => $iis['ii'],
            'ii2' => $iis['ii2']
        );
    }

    protected function compute_ii($canvas, $image_width, $image_height ){
        $ii_w = $image_width+1;
        $ii_h = $image_height+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++ ){
                $rgb = ImageColorAt($canvas, $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] + $rowsum2;
            }
        }
        return array('ii'=>$ii, 'ii2' => $ii2);
    }

    protected function do_detect_greedy_big_to_small( $ii, $ii2, $width, $height ){
        $s_w = $width/20.0;
        $s_h = $height/20.0;
        $start_scale = $s_h < $s_w ? $s_h : $s_w;
        $scale_update = 1 / 1.2;
        $offset = self::$offset;
        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 ){

                    // ignore existing face areas
                    $continue = false;
                    if ( is_array( $this->faces ) ) {
                        foreach( $this->faces as $face ) {
                            if ( $face && $x >= $face['x'] - $offset && $x + $face['w'] - $offset <= $face['x'] + $face['w'] && $y >= $face['y'] - $offset && $y + $face['w'] - $offset <= $face['y'] + $face['w'] ) {
                                $continue = true;
                                $x += $face['w']; // skip ahead
                            }
                        }
                    }

                    if ( $continue )
                        continue;

                    $passed = $this->detect_on_sub_image( $x, $y, $scale, $ii, $ii2, $w, $width+1, $inv_area);
                    if( $passed ) {
                        $this->faces[] = array('x'=>$x, 'y'=>$y, 'w'=>$w);
                    }
                } // end x
            } // end y
        }  // end scale
        return null;
    }

    protected function detect_on_sub_image( $x, $y, $scale, $ii, $ii2, $w, $iiw, $inv_area){
        $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;

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

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

            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;
                    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;
    }
}