php 生成等比缩略图

<?
/**
* $filename:   源图片
* $targetfile: 保存图片位置
* $maxwidth:   保存图片宽
* $maxheight:  保存图片高
* demo:        resizeimage('./1.jpg', 500, 250, './2.jpg');
*/
function resizeimage($filename, $maxwidth, $maxheight, $targetfile){
	if(file_exists($filename)){
		$size = getimagesize($filename);
		switch($size[2]){ 
			case 1: 
				$im = @imagecreatefromgif($filename); 
				break; 
			case 2: 
				$im = @imagecreatefromjpeg($filename); 
				break; 
			case 3: 
				$im = @imagecreatefrompng($filename); 
				break; 
		}
	}else{
		return false;
	}

	$width  = imagesx($im);
	$height = imagesy($im);
	if(($maxwidth && $width > $maxwidth) && ($maxheight && $height > $maxheight)){
		if($maxwidth && $width > $maxwidth){
			$widthratio = $maxwidth/$width;
			$resizewidth = true;
		}
		if($maxheight && $height > $maxheight){
			$heightratio = $maxheight/$height;
			$resizeheight = true;
		}
		if($resizewidth && $resizeheight){
			if($widthratio < $heightratio){
				$ratio = $widthratio;
			}else{
				$ratio = $heightratio;
			}
		}elseif($resizewidth){
			$ratio = $widthratio;
		}elseif($resizeheight){
			$ratio = $heightratio;
		}
		$newwidth = $width * $ratio;
		$newheight = $height * $ratio;
		if(function_exists("imagecopyresampled")){
			$newim = imagecreatetruecolor($newwidth, $newheight);
			imagecopyresampled($newim, $im, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);
		}else{
			$newim = imagecreate($newwidth, $newheight);
			imagecopyresized($newim, $im, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);
		}
		imagejpeg($newim, $targetfile ? $targetfile : $filename);
		imagedestroy($newim);
	}else{
		imagejpeg($im, $filename);
		imagedestroy($im);
	}
}

?>