Smileys and Parser.php

Hello iam having a slight problem. I would like to display my smileys at there actual sizes instead of jsut having one specific size for every smiley.

Here are the few lines of code that seem to be limiting my smileys to a certain size.

for ($i = 0; $i < $num_smilies; ++$i)
        $text = preg_replace("#(?<=.\W|\W.|^\W)".preg_quote($smiley_text[$i], '#')."(?=.\W|\W.|\W$)#m", '$1<img src="img/smilies/'.$smiley_img[$i].'" width="15" height="15" alt="'.substr($smiley_img[$i], 0, strrpos($smiley_img[$i], '.')).'" />$2', $text);

How should i change this code in order to fix this small problem of mine.

Help woulld be greatly appreciated