Image auto cropping

class.image_auto_crop.inc.php

<?php

namespace Spot;

define('USE_GDLIB', FALSE);

class ImageAutoCrop {
    protected static function get_line_contrast($img, $y) {
        $contrast = 0;
        $x = 0;
        $oldlevel = FALSE;
        if (USE_GDLIB === FALSE) {
            $width = imageWidth($img);
        } else {
            $width = imagesx($img);
        }
        do {
            if (USE_GDLIB === FALSE) {
                list($r_, $g_, $b_, $a_) = get($img, $x, $y);
                $r = (int) round($r_ * 255.0);
                $g = (int) round($g_ * 255.0);
                $b = (int) round($b_ * 255.0);                
            } else {
                $rgb = imagecolorat($img, $x, $y);
                $r = ($rgb >> 16) & 0xff;
                $g = ($rgb >> 8) & 0xff;
                $b = $rgb & 0xff;
            }
            $level = ($r * 77 + $g * 151 + $b * 28 + 128) >> 8;
            if ($oldlevel !== FALSE) {
                if ($oldlevel > $level) {
                    $contrast += $oldlevel - $level;
                } else {
                    $contrast += $level - $oldlevel;            
                }
            }
            $oldlevel = $level;
            $x++;
        } while ($x < $width);
        
        return $contrast;
    }
    
    protected static function get_column_contrast($img, $x) {
        $contrast = 0;
        $y = 0;
        $oldlevel = FALSE;
        if (USE_GDLIB === FALSE) {
            $width = imageHeight($img);            
        } else {
            $width = imagesy($img);
        }
        do {
            if (USE_GDLIB === FALSE) {
                list($r_, $g_, $b_, $a_) = get($img, $x, $y);                
                $r = (int) round($r_ * 255.0);
                $g = (int) round($g_ * 255.0);
                $b = (int) round($b_ * 255.0);                
            } else {
                $rgb = imagecolorat($img, $x, $y);
                $r = ($rgb >> 16) & 0xff;
                $g = ($rgb >> 8) & 0xff;
                $b = $rgb & 0xff;
            }
            $level = ($r * 77 + $g * 151 + $b * 28 + 128) / 256;
            if ($oldlevel !== FALSE) {
                if ($oldlevel > $level) {
                    $contrast += $oldlevel - $level;
                } else {
                    $contrast += $level - $oldlevel;            
                }
            }
            $oldlevel = $level;
            $y++;
        } while ($y < $width);

        return $contrast;
    }
    
    protected static function get_max_cropping_ratio() {
        return 0.25;
    }
    
    protected static function get_contrast_barrier_for_cropping() {
        return 0.032;
    }
    
    protected static function get_autocrop_edges($img, $contrast_barrier_for_cropping,
                                                 $max_cropping_ratio, $x0, $y0, $x1, $y1) {
        $width = 1 + $x1 - $x0;
        $height = 1 + $y1 - $y0;
        if ($width < 2 || $height < 2) {
            return FALSE;
        }
        $line_contrasts = array();
        $total_contrast = 0;
        $y = $y0;
        do {
            $line_contrasts[$y] = self::get_line_contrast($img, $y);
            $total_contrast += $line_contrasts[$y];
            $y++;
        } while ($y <= $y1);
        $cutoff_contrast = round($total_contrast * $contrast_barrier_for_cropping);
        $local_contrast = 0;    
        $crop_y0 = $y0;
        $crop_y0_max = $y0 + floor($height * $max_cropping_ratio);
        do {
            $local_contrast += $line_contrasts[$crop_y0];
            if ($local_contrast >= $cutoff_contrast) {
                break;
            }
            $crop_y0++;
        } while ($crop_y0 <= $y1 && $crop_y0 < $crop_y0_max);
        $local_contrast = 0;
        $crop_y1 = $y1;
        $crop_y1_min = $y1 - floor($height * $max_cropping_ratio);
        do {
            $local_contrast += $line_contrasts[$crop_y1];
            if ($local_contrast >= $cutoff_contrast) {
                break;
            }
            $crop_y1--;
        } while ($crop_y1 >= $y0 && $crop_y1 > $crop_y1_min);
        
        $local_contrast = 0;
        $crop_x0 = $x0;
        $crop_x0_max = $x0 + floor($width * $max_cropping_ratio);
        do {
            $local_contrast += self::get_column_contrast($img, $crop_x0);
            if ($local_contrast >= $cutoff_contrast) {
                break;
            }
            $crop_x0++;
        } while ($crop_x0 <= $x1 && $crop_x0 < $crop_x0_max);
        $local_contrast = $x0;
        $crop_x1 = $x1;
        $crop_x1_min = $x1 - floor($width * $max_cropping_ratio);
        do {
            $local_contrast += self::get_column_contrast($img, $crop_x1);
            if ($local_contrast >= $cutoff_contrast) {
                break;
            }
            $crop_x1--;
        } while ($crop_x1 >= $x0 && $crop_x1 > $crop_x1_min);
        return array('crop_x0' => $crop_x0, 'crop_x1' => $crop_x1,
                     'crop_y0' => $crop_y0, 'crop_y1' => $crop_y1);
    }
    
    static function autocrop($img) {
        if (USE_GDLIB === FALSE) {
            $width = imageWidth($img);
            $height = imageHeight($img);
        } else {
            $width = imagesx($img); 
            $height = imagesy($img);
        }
        $edges = self::get_autocrop_edges($img, self::get_contrast_barrier_for_cropping(),
                                          self::get_max_cropping_ratio(),
                                          0, 0, $width - 1, $height -1);
        if ($edges === FALSE) {
            return FALSE;
        }
        $crop_x0 = $edges['crop_x0'];
        $crop_x1 = $edges['crop_x1'];
        $crop_y0 = $edges['crop_y0'];
        $crop_y1 = $edges['crop_y1'];
        
        $new_edges = self::get_autocrop_edges($img, self::get_contrast_barrier_for_cropping(),
                                              self::get_max_cropping_ratio(),
                                              $crop_x0, $crop_y0, $crop_x1, $crop_y1);
        $new_center_x = ($new_edges['crop_x0'] + $new_edges['crop_x1']) / 2;
        $new_center_y = ($new_edges['crop_y0'] + $new_edges['crop_y1']) / 2;
        
        $new_width = 1 + $crop_x1 - $crop_x0;
        $new_height = 1 + $crop_y1 - $crop_y0;
        
        $original_ratio = (double) $width / (double) $height;
        $new_ratio = (double) $new_width / (double) $new_height;
        $new_height_with_xcrop = $new_width / $original_ratio;
        $new_width_with_ycrop = $new_height * $original_ratio;  
        $xcrop = FALSE;
        $ycrop = FALSE;
        if ($new_height_with_xcrop / (double) $height < $new_width_with_ycrop / (double) $width) {
            $ycrop = TRUE;
        } else {
            $xcrop = TRUE;
        }
        if ($xcrop === TRUE) {
            $t = $new_height_with_xcrop / 2;
            if ($new_center_y < $t) {
                $crop_y0 = 0;
            } elseif ($new_center_y >= $height - $t) {
                $crop_y0 = $height - $new_height_with_xcrop;
            } else {
                $crop_y0 = $new_center_y - $t;
            }
            $new_height = $new_height_with_xcrop;
        } else {
            $t = $new_width_with_ycrop / 2; 
            if ($new_center_x < $t) {           
                $crop_x0 = 0;
            } elseif ($new_center_x >= $width - $t) {
                $crop_x0 = $width - $new_width_with_ycrop;
            } else {
                $crop_x0 = $new_center_x - $t;
            }
            $new_width = $new_width_with_ycrop;
        }
        return array('offsetx' => (int) $crop_x0, 'offsety' => (int) $crop_y0,
                     'width' => (int) $new_width, 'height' => (int) $new_height);
    }    
}