PHP - 自定义验证码未调整大小

我找到了一些自定义验证码代码，它运行良好，但我无法调整它的大小。我的目标是让它高 28px，但每当我将"高度"变量更改为 28 时，它就会扭曲，它保持相同的大小，只是文本变得更大且不可读。我不知道还有什么要改变的，你能帮我吗？

session_start(); 
$text = rand(100,999).'-'.rand(100,999); 
$_SESSION["vercode"] = $text; 
$height = 80; 
$width = 130; 

$image_p = imagecreate($width, $height); 
$height = 1; 
$width = 5;
$noiseColor = imagecolorallocate($image_p, rand(50,255), rand(50,250), rand(50,255));// Sets the color of the interference
for( $i = 0; $i < ($width * $height)/150; $i++ ) 
{
    imageline($image_p, mt_rand(0, $width), mt_rand(0, $height), mt_rand(0, $width), mt_rand(0, $height), $noiseColor);
}

$black = imagecolorallocate($image_p, 255, 255, 255); 
$white = imagecolorallocate($image_p, 0, 0, 0); 
$font_size = 14;  
imagestring($image_p, $font_size, rand(20,32), rand(10,40), $text, $white); 
imagejpeg($image_p, null, 80);