how to change font size when write picture

hi: I am a new user. I want to make a program which will make a button. I draw the button but when I write text at it, I have meet some question. First , I do not know how to change the text size.The system give 5 font size, but I want define the size by myself.Please help me , thank you . the source is under here. $im = imagecreate($width,$height); $imagebackcolor = ImageColorAllocate($im, intval("0x".substr($backcolor,0,2),16),intval("0x".substr($backcolor,2,2),16),intval("0x".substr($backcolor,4,2),16)); $imagetextcolor = ImageColorAllocate($im, intval("0x".substr($textcolor,0,2),16),intval("0x".substr($textcolor,2,2),16),intval("0x".substr($textcolor,4,2),16)); imagestring($im, $textfont,$textplacex, $textplacey, $text, $imagetextcolor); Imagejpeg($im); ImageDestroy($im);