Index: branches/RC/core/units/general/helpers/image_helper.php
===================================================================
diff -u -N -r9256 -r9278
--- branches/RC/core/units/general/helpers/image_helper.php	(.../image_helper.php)	(revision 9256)
+++ branches/RC/core/units/general/helpers/image_helper.php	(.../image_helper.php)	(revision 9278)
@@ -60,21 +60,28 @@
 			if (function_exists('imagecreatefromjpeg')) {
 				// try to resize using GD
 				$resize_map = Array (
-					'image/jpeg' => 'imagecreatefromjpeg:imagejpeg',
-					'image/gif' => 'imagecreatefromgif:imagegif',
-					'image/png' => 'imagecreatefrompng:imagepng',
+					'image/jpeg' => 'imagecreatefromjpeg:imagejpeg:jpg',
+					'image/gif' => 'imagecreatefromgif:imagegif:gif',
+					'image/png' => 'imagecreatefrompng:imagepng:png',
 				);
 
 				$mime_type = $image_info['mime'];
 				if (!isset($resize_map[$mime_type])) {
 					return false;
 				}
 
-				list ($read_function, $write_function) = explode(':', $resize_map[$mime_type]);
+				list ($read_function, $write_function, $file_extension) = explode(':', $resize_map[$mime_type]);
 
 				$src_image_rs = @$read_function($src_image);
 				if ($src_image_rs) {
 					$dst_image_rs = imagecreatetruecolor($dst_width, $dst_height);
+
+					if ($file_extension == 'png') {
+						// preserve transparency of PNG images
+						$transparent_color = imagecolorallocate($dst_image_rs, 0, 0, 0);
+						imagecolortransparent($dst_image_rs, $transparent_color);
+					}
+
 					imagecopyresampled($dst_image_rs, $src_image_rs, 0, 0, 0, 0, $dst_width, $dst_height, $image_info[0], $image_info[1]);
 					return @$write_function($dst_image_rs, $dst_image, 100);
 				}