Image filtering methods.

brightness.php

<?php

// ref: http://www.phpied.com/image-fun-with-php-part-2/
// ref: http://www.php.net/manual/en/function.imagefilter.php

require('./image.php');
$value = (int) $_GET['value'];

$image = imagecreatefromjpeg($imagefile);
header("Content-type: image/jpeg");
imagefilter($image, IMG_FILTER_BRIGHTNESS, $value);
imagejpeg($image);
imagedestroy($image);

?>

contrast.php

<?php

// ref: http://www.phpied.com/image-fun-with-php-part-2/
// ref: http://www.php.net/manual/en/function.imagefilter.php

require('./image.php');
$value = (int) $_GET['value'];

$image = imagecreatefromjpeg($imagefile);
header("Content-type: image/jpeg");
imagefilter($image, IMG_FILTER_CONTRAST, $value);
imagejpeg($image);
imagedestroy($image);

?>

greyscale.php

<?php

// ref: http://www.phpied.com/image-fun-with-php-part-2/
// ref: http://www.php.net/manual/en/function.imagefilter.php

require('./image.php');

$image = imagecreatefromjpeg($imagefile);
header("Content-type: image/jpeg");
imagefilter($image, IMG_FILTER_GRAYSCALE);
imagejpeg($image);
imagedestroy($image);

?>

hue.php

<?php

// ref: http://stackoverflow.com/questions/1890409/change-hue-of-an-image-with-php-gd-library

function imagehue(&$image, $angle) {
  if($angle % 360 == 0) return;
  $width = imagesx($image);
  $height = imagesy($image);

  for($x = 0; $x < $width; $x++) {
    for($y = 0; $y < $height; $y++) {
      $rgb = imagecolorat($image, $x, $y);
      $r = ($rgb >> 16) & 0xFF;
      $g = ($rgb >> 8) & 0xFF;
      $b = $rgb & 0xFF;            
      $alpha = ($rgb & 0x7F000000) >> 24;
      list($h, $s, $l) = rgb2hsl($r, $g, $b);
      $h += $angle / 360;
      if($h > 1) $h--;
      list($r, $g, $b) = hsl2rgb($h, $s, $l);            
      imagesetpixel($image, $x, $y, imagecolorallocatealpha($image, $r, $g, $b, $alpha));
    }
  }
}

function rgb2hsl($r, $g, $b) {
  $var_R = ($r / 255);
  $var_G = ($g / 255);
  $var_B = ($b / 255);
  
  $var_Min = min($var_R, $var_G, $var_B);
  $var_Max = max($var_R, $var_G, $var_B);
  $del_Max = $var_Max - $var_Min;
  
  $v = $var_Max;
  
  if ($del_Max == 0) {
    $h = 0;
    $s = 0;
  } else {
    $s = $del_Max / $var_Max;
  
    $del_R = ( ( ( $var_Max - $var_R ) / 6 ) + ( $del_Max / 2 ) ) / $del_Max;
    $del_G = ( ( ( $var_Max - $var_G ) / 6 ) + ( $del_Max / 2 ) ) / $del_Max;
    $del_B = ( ( ( $var_Max - $var_B ) / 6 ) + ( $del_Max / 2 ) ) / $del_Max;
  
    if      ($var_R == $var_Max) $h = $del_B - $del_G;
    else if ($var_G == $var_Max) $h = ( 1 / 3 ) + $del_R - $del_B;
    else if ($var_B == $var_Max) $h = ( 2 / 3 ) + $del_G - $del_R;
  
    if ($h < 0) $h++;
    if ($h > 1) $h--;
  }
  
  return array($h, $s, $v);
}

function hsl2rgb($h, $s, $v) {
  if($s == 0) {
    $r = $g = $B = $v * 255;
  } else {
    $var_H = $h * 6;
    $var_i = floor( $var_H );
    $var_1 = $v * ( 1 - $s );
    $var_2 = $v * ( 1 - $s * ( $var_H - $var_i ) );
    $var_3 = $v * ( 1 - $s * (1 - ( $var_H - $var_i ) ) );

    if       ($var_i == 0) { $var_R = $v     ; $var_G = $var_3  ; $var_B = $var_1 ; }
    else if  ($var_i == 1) { $var_R = $var_2 ; $var_G = $v      ; $var_B = $var_1 ; }
    else if  ($var_i == 2) { $var_R = $var_1 ; $var_G = $v      ; $var_B = $var_3 ; }
    else if  ($var_i == 3) { $var_R = $var_1 ; $var_G = $var_2  ; $var_B = $v     ; }
    else if  ($var_i == 4) { $var_R = $var_3 ; $var_G = $var_1  ; $var_B = $v     ; }
    else                   { $var_R = $v     ; $var_G = $var_1  ; $var_B = $var_2 ; }

    $r = $var_R * 255;
    $g = $var_G * 255;
    $B = $var_B * 255;
  }    
  return array($r, $g, $B);
}

require('./image.php');
$value = (float) $_GET['value'];

$image = imagecreatefromjpeg($imagefile);
header("Content-type: image/jpeg");
imagehue($image, $value);
imagejpeg($image);
imagedestroy($image);

?>

image.php

<?php

switch ($_GET['image']) {
	case "nathalie.jpg":
	case "mg5652.jpg":
	  $imagefile = $_GET['image'];
	  break;
  default:
    die(header($_SERVER['SERVER_PROTOCOL'] . ' 500 Internal Server Error', true, 500));
}

?>

saturation.php

<?php

// ref: http://stackoverflow.com/questions/1890409/change-hue-of-an-image-with-php-gd-library

function imagesaturation(&$image, $change) {
  $width = imagesx($image);
  $height = imagesy($image);

  for($x = 0; $x < $width; $x++) {
    for($y = 0; $y < $height; $y++) {
      $rgb = imagecolorat($image, $x, $y);
      $r = ($rgb >> 16) & 0xFF;
      $g = ($rgb >> 8) & 0xFF;
      $b = $rgb & 0xFF;            
      $alpha = ($rgb & 0x7F000000) >> 24;
      list($h, $s, $l) = rgb2hsl($r, $g, $b);
      $s = $s * $change;
      if($s > 1) $s = 1;
      if($s < 0) $s = 0;
      list($r, $g, $b) = hsl2rgb($h, $s, $l);            
      imagesetpixel($image, $x, $y, imagecolorallocatealpha($image, $r, $g, $b, $alpha));
    }
  }
}

function rgb2hsl($r, $g, $b) {
  $var_R = ($r / 255);
  $var_G = ($g / 255);
  $var_B = ($b / 255);
  
  $var_Min = min($var_R, $var_G, $var_B);
  $var_Max = max($var_R, $var_G, $var_B);
  $del_Max = $var_Max - $var_Min;
  
  $v = $var_Max;
  
  if ($del_Max == 0) {
    $h = 0;
    $s = 0;
  } else {
    $s = $del_Max / $var_Max;
  
    $del_R = ( ( ( $var_Max - $var_R ) / 6 ) + ( $del_Max / 2 ) ) / $del_Max;
    $del_G = ( ( ( $var_Max - $var_G ) / 6 ) + ( $del_Max / 2 ) ) / $del_Max;
    $del_B = ( ( ( $var_Max - $var_B ) / 6 ) + ( $del_Max / 2 ) ) / $del_Max;
  
    if      ($var_R == $var_Max) $h = $del_B - $del_G;
    else if ($var_G == $var_Max) $h = ( 1 / 3 ) + $del_R - $del_B;
    else if ($var_B == $var_Max) $h = ( 2 / 3 ) + $del_G - $del_R;
  
    if ($h < 0) $h++;
    if ($h > 1) $h--;
  }
  
  return array($h, $s, $v);
}

function hsl2rgb($h, $s, $v) {
  if($s == 0) {
    $r = $g = $B = $v * 255;
  } else {
    $var_H = $h * 6;
    $var_i = floor( $var_H );
    $var_1 = $v * ( 1 - $s );
    $var_2 = $v * ( 1 - $s * ( $var_H - $var_i ) );
    $var_3 = $v * ( 1 - $s * (1 - ( $var_H - $var_i ) ) );

    if       ($var_i == 0) { $var_R = $v     ; $var_G = $var_3  ; $var_B = $var_1 ; }
    else if  ($var_i == 1) { $var_R = $var_2 ; $var_G = $v      ; $var_B = $var_1 ; }
    else if  ($var_i == 2) { $var_R = $var_1 ; $var_G = $v      ; $var_B = $var_3 ; }
    else if  ($var_i == 3) { $var_R = $var_1 ; $var_G = $var_2  ; $var_B = $v     ; }
    else if  ($var_i == 4) { $var_R = $var_3 ; $var_G = $var_1  ; $var_B = $v     ; }
    else                   { $var_R = $v     ; $var_G = $var_1  ; $var_B = $var_2 ; }

    $r = $var_R * 255;
    $g = $var_G * 255;
    $B = $var_B * 255;
  }    
  return array($r, $g, $B);
}

require('./image.php');
$value = abs((float) $_GET['value']);

$image = imagecreatefromjpeg($imagefile);
header("Content-type: image/jpeg");
imagesaturation($image, $value);
imagejpeg($image);
imagedestroy($image);

?>

sharpen.php

<?php 

// ref: http://us1.php.net/imageconvolution
// ref: http://loriweb.pair.com/8udf-basics.html
// ref: http://loriweb.pair.com/8udf-sharpen.html

require('./image.php');
$value = abs((float) $_GET['value']);

$image = imagecreatefromjpeg($imagefile);
header("Content-type: image/png");

$sharpenMatrix = array( 
  array(-1.2, -1, -1.2), 
  array(-1, $value, -1), 
  array(-1.2, -1, -1.2) 
  ); 

// calculate the sharpen divisor 
$divisor = array_sum(array_map('array_sum', $sharpenMatrix));

$offset = 0; 

// apply the matrix 
imageconvolution($image, $sharpenMatrix, $divisor, $offset);

imagepng($image);
imagedestroy($image);

?>