PHP: Converting png's and gif's into grayscale

Question

Hello, im using the following script to convert jpgs into grayscale-images. http://bubble.ro/How_to_convert_an_image_to_grayscale_using_PHP.html

i want to upgrade it to also convert pngs (with transparency) and gifs (with transparency) into grayscale images.

At the moment it's not working. I'm querying the image-src for its file-extension. If jpg, if, gif, or if png i call the appropriate imagecreatefrom-jpg-gif-png

However i'm always running the same for-loop and gifs unfortunately only get gray rectangles, every pixel is gray. Png's almost work, however transprency in pngs gets transformed to black.

Any ideas?

Answer 1

Use this found here http://hm2k.googlecode.com/svn/trunk/code/php/functions/imagegray.php

<?php

function imagegray($img) {
  if (!file_exists($img)) { user_error("'$img' file was not found."); return; }
  list($width, $height, $type) = getimagesize($img);
  switch ($type) {
    case 1:
    $img = imagecreatefromgif($img);
    break;
    case 2:
    $img = imagecreatefromjpeg($img);
    break;
    case 3:
    default:
    $img = imagecreatefrompng($img);
    break;
  }
  imagefilter($img, IMG_FILTER_GRAYSCALE);
  header('Content-type: image/png');
  imagepng($img);
  imagedestroy($img);
}

/*because i'm british*/
function imagegrey($img) {
  return imagegray($img);
}

/*

//example usage

$i=isset($_REQUEST['i'])?$_REQUEST['i']:'';
if ($i) { imagegrey($i); }

*/

Answer 2

$image = ImageCreateFromString(file_get_contents('/path/to/image.ext'));

ImageFilter($image, IMG_FILTER_GRAYSCALE);

ImageGIF($image); // or ImagePNG($image);

Answer 3

thank you!

imagefilter($img, IMG_FILTER_GRAYSCALE);

it's almost working. i'm still having problems with transprency. pngs with transparent background get transformed to black (the background is black). The same happens to gifs and moreover gifs with transprency don't get properly grayscaled. There are a few very graytoned colors, however there are pale greentones and redtones in it.

<?php                                                                       
$src = $_GET['src'];

$img_ext;
if (preg_match('/\.(\w{3,4})$/i', $src, $reg)) {
    $img_ext = strtolower($reg[1]);
}

$source_file = $src;
if ($img_ext == "jpg" || $img_ext == "jpeg") { //jpg
    $im = imagecreatefromjpeg($source_file);
} else if ($img_ext == "gif") {
    $im = imagecreatefromgif($source_file); //gif
} else if ($img_ext == "png") {
    $im = imagecreatefrompng($source_file); //png
} else {
}

ImageFilter($im, IMG_FILTER_GRAYSCALE);


if ($img_ext == "jpg" || $img_ext == "jpeg") { //jpg
    header('Content-type: image/jpeg');
    imagejpeg($im);
} else if ($img_ext == "gif") { //gif
    header('Content-type: image/gif');
    imagegif($im);
} else if ($img_ext == "png") { //png
    header('Content-type: image/png');
    imagepng($im);
} else {
}

?>