Hi Namrata,

for pie chart u can use following methods:

$graph->set_title_font("/usr/share/fonts/ttf/windows/times.ttf",18);
$graph->set_value_font("/usr/share/fonts/ttf/windows/times.ttf",12);
$graph->set_label_font("/usr/share/fonts/ttf/windows/times.ttf",14);
[download]

where 1st argument is font type & second one is font size :)