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:

<?php 
$w?$resizewidth=$w:$resizewidth=400;// 生成图片的宽度 
$h?$resizeheight=$h:$resizeheight=400;// 生成图片的高度 
function resizeimage($im,$maxwidth,$maxheight,$name){ 
    $width = imagesx($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,$name); 
        imagedestroy ($newim); 
    }else{ 
        imagejpeg ($im,$name); 
    } 
} 
if($_files['uploadfile']['size']){ 
    if($_files['uploadfile']['type'] == "image/pjpeg"){ 
        $im = imagecreatefromjpeg($_files['uploadfile']['tmp_name']); 
    }elseif($_files['uploadfile']['type'] == "image/x-png"){ 
        $im = imagecreatefrompng($_files['uploadfile']['tmp_name']); 
    }elseif($_files['uploadfile']['type'] == "image/gif"){ 
        $im = imagecreatefromgif($_files['uploadfile']['tmp_name']); 
    } 
    if($im){ 
        if(file_exists('bbs.jpg')){ 
            unlink('bbs.jpg'); 
        } 
        resizeimage($im,$resizewidth,$resizeheight,'bbs.jpg'); 
        imagedestroy ($im); 
   
    } 
} 
//$uploadfile="www.phprm.com.jpg";

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