Image transparency in imagepng() and imagegif() - php

Question

I want to resize 2 types of images (png, gif) with transparent background...
But in png it works well in big size of the original image.
eg. Original file dimension is 150x150
change into 200x200 or exceeding the original size it works well. but in 100x100 it displays
Then the last GIF it doesn't work.
Here my code for png
$new_img = imagecreatetruecolor($max_w, $max_h);
imagealphablending($new_img, false);
imagesavealpha($new_img, true);
$transparentindex = imagecolorallocatealpha($new_img, 255, 255, 255, 127);
imagefill($new_img, 0, 0, $transparentindex);
imagepng($new_img, $dir);
Here my code for gif
imagegif($new_img, $dir);

Answer 1

I know no PHP, but this seems to do the trick:
#!/usr/local/bin/php -f
<?php
$neww=100;
$newh=100;
// Load original image and get its dimensions
$img = imagecreatefrompng("badge.png");
$w=imagesx($img);
$h=imagesy($img);
// Create output image, and fill with lots of transparency
$out = imagecreatetruecolor($neww,$newh);
imagealphablending($out,false);
$transparentindex = imagecolorallocatealpha($out,0,0,0,127);
imagefill($out,0,0,$transparentindex);
imagesavealpha($out, true);
// Copy original image, reized on top
imagecopyresized($out,$img,0,0,0,0,$neww,$newh,$w,$h);
imagepng($out,"out.png");
?>

Answer 2

Here is a little hack :)
Don't have any other ideas.
It involves a second image (1x1 trasparent gif)
create image
resize
create a transparent background with same size as resized image
use imagecolortransparent() to get the rgb index
imagecopymerge() images
voilà
.
$dir = 'http://i.stack.imgur.com/DbhrJ.png';
$max_w = 50;
$max_h = 50;
// get image size
list($src_w, $src_h) = getimagesize($dir);
if ($src_w > $max_w) {
$ratio = $max_w / $src_w;
$max_w = $src_w * $ratio;
}
else if ($src_h > $max_h) {
$ratio = $max_h / $src_h;
$max_h = $src_h * $ratio;
}
// resize image to $max_w and $max_h, and also save alpha
$src = imagecreatefromstring(file_get_contents($dir));
$new_img = imagecreatetruecolor($max_w, $max_h);
imagealphablending($new_img, false);
imagesavealpha($new_img, true);
imagecopyresampled($new_img, $src, 0, 0, 0, 0, $max_w, $max_h, $src_w, $src_h);
// create a new image with $max_w and $max_h
$maxsize = imagecreatetruecolor($max_w, $max_h);
// add 1x1 gif and resize, then copy over $maxsize
$background = imagecreatefromgif("http://i.imgur.com/atRjCdk.gif"); // transparent 1x1 gif
imagecopyresampled($maxsize, $background, 0, 0, 0, 0, $max_w, $max_h, 1, 1);
// allocate transparency
$transparent = imagecolortransparent($maxsize);
$transparent_index = imagecolorallocate($maxsize, $transparent['red'], $transparent['green'], $transparent['blue']);
imagecolortransparent($maxsize, $transparent_index);
// image copy
imagecopymerge($maxsize, $new_img, 0, 0, 0, 0, $max_w, $max_h, 100);
// save or output
imagegif($maxsize, $path_to_save);
// destroy images
imagedestroy($maxsize);
imagedestroy($new_img);
imagedestroy($background);
imagedestroy($src);