Dynamic image from text and 24bit PNG transparency

[r0b0t]

I'm trying to write a function that creates 24bit PNG's with transparent backgrounds from strings. I used [url=http://www.alistapart.com/articles/dynatext]A List Apart's dynamic text replacement function[/url] as a starting point but the edges were aliasing on the edges didn't work with the multicolored background images on the site that the titles were intended for.

I simplified and modified the code and [url=http://www.uventus.com/dynamic_text.html]the resulting image[/url] looked better around the edges of the font but left blocks of the black background generated by the imagecreatetruecolor function. I tried the function in two different environments: PHP 5.1.1/Windows XP/Apache 2/GD 2.0.28 and PHP 4.3.2/Fedora Enterprise 3/GD 2.0.12 and received the same results.

Code and example image link are below. Thanks in advance for any advice.
-Chris


Example Image: [url=http://www.uventus.com/dynamic_text.html]http://www.uventus.com/dynamic_text.html[/url]
[img]http://www.uventus.com/dyanamic_text.png[/img]
Code:
[code]  php:function toPng($str, $font_file, $font_size, $font_color,  $destination)
    {
        $font_rgb = hex_to_rgb($font_color) ;
        $dip = get_dip($font_file,$font_size) ;
        $box = imagettfbbox($font_size,0,$font_file,$str) ;
        $image = imagecreatetruecolor(abs($box[2]-$box[0]),abs($box[5]-$dip)) ;
        imagesavealpha($image, true);
        imagealphablending($image, false);
        $background_color =  imagecolorallocate($image, 0, 0, 0) ;
        $font_color = imagecolorallocate($image,$font_rgb['red'], $font_rgb['green'],$font_rgb['blue']) ; 
        imagettftext($image,$font_size,0,-$box[0],abs($box[5]-$box[3])-$box[1], $font_color, $font_file, $str) ;   
        imagecolortransparent($image, $background_color) ;
        imagepng($image, $destination) ;
        imagedestroy($image) ;
    }
    function get_dip($font,$size)
    {
        $test_chars = 'abcdefghijklmnopqrstuvwxyz' .
                      'abcdefghijklmnopqrstuvwxyz' .
                      '1234567890' .
                      '!#$%^&*()\'"\\/;.,`~<>[]{}-+_-=' ;
        $box = imagettfbbox($size,0,$font,$test_chars) ;
        return $box[3] ;
    }
    function hex_to_rgb($hex)
    {
        if(substr($hex,0,1) == '#')
            $hex = substr($hex,1) ;
        if(strlen($hex) == 3)
        {
            $hex = substr($hex,0,1) . substr($hex,0,1) .
                  substr($hex,1,1) . substr($hex,1,1) .
                  substr($hex,2,1) . substr($hex,2,1) ;
        }

        if(strlen($hex) != 6)
        {
        }
        $rgb['red'] = hexdec(substr($hex,0,2)) ;
        $rgb['green'] = hexdec(substr($hex,2,2)) ;
        $rgb['blue'] = hexdec(substr($hex,4,2)) ;

        return $rgb ;
    }
    ?>[/code]