本程序是根据用户上传图片后再把上传的图片按比例生成缩略图,程序实例代码如下:

1. <?php 
2. $w?$resizewidth=$w:$resizewidth=400;// 生成图片的宽度 
3. $h?$resizeheight=$h:$resizeheight=400;// 生成图片的高度 
4. function resizeimage($im,$maxwidth,$maxheight,$name){ 
5.     $width = imagesx($im); 
6.     $height = imagesy($im); 
7.     if(($maxwidth && $width > $maxwidth) || ($maxheight && $height > $maxheight)){ 
8.         if($maxwidth && $width > $maxwidth){ 
9.             $widthratio = $maxwidth/$width; 
10.             $resizewidth=true; 
11.         } 
12.         if($maxheight && $height > $maxheight){ 
13.             $heightratio = $maxheight/$height; 
14.             $resizeheight=true; 
15.         } 
16.         if($resizewidth && $resizeheight){ 
17.             if($widthratio < $heightratio){ 
18.                 $ratio = $widthratio; 
19.             }else{ 
20.                 $ratio = $heightratio; 
21.             } 
22.         }elseif($resizewidth){ 
23.             $ratio = $widthratio; 
24.         }elseif($resizeheight){ 
25.             $ratio = $heightratio; 
26.         } 
27.         $newwidth = $width * $ratio; 
28.         $newheight = $height * $ratio; 
29.         if(function_exists("imagecopyresampled")){ 
30.               $newim = imagecreatetruecolor($newwidth, $newheight); 
31.               imagecopyresampled($newim, $im, 0, 0, 0, 0, $newwidth, $newheight, $width, $height); 
32.         }else{ 
33.             $newim = imagecreate($newwidth, $newheight); 
34.               imagecopyresized($newim, $im, 0, 0, 0, 0, $newwidth, $newheight, $width, $height); 
35.         } 
36.         imagejpeg ($newim,$name); 
37.         imagedestroy ($newim); 
38.     }else{ 
39.         imagejpeg ($im,$name); 
40.     } 
41. } 
42. if($_files['uploadfile']['size']){ 
43.     if($_files['uploadfile']['type'] == "image/pjpeg"){ 
44.         $im = imagecreatefromjpeg($_files['uploadfile']['tmp_name']); 
45.     }elseif($_files['uploadfile']['type'] == "image/x-png"){ 
46.         $im = imagecreatefrompng($_files['uploadfile']['tmp_name']); 
47.     }elseif($_files['uploadfile']['type'] == "image/gif"){ 
48.         $im = imagecreatefromgif($_files['uploadfile']['tmp_name']); 
49.     } 
50.     if($im){ 
51.         if(file_exists('bbs.jpg')){ 
52.             unlink('bbs.jpg'); 
53.         } 
54.         resizeimage($im,$resizewidth,$resizeheight,'bbs.jpg'); 
55.         imagedestroy ($im); 
56.    
57.     } 
58. } 
59. //$uploadfile="www.phpfensi.com.jpg"; 
60. ?> 
61.  

出处：http://www.phpfensi.com/php/20140817/4348.html