php生成图片缩略图的入门例子

function make_thumb($src,$dest,$desired_width)
{
 
  /* read the source image */
  $source_image = imagecreatefromjpeg($src);
  $width = imagesx($source_image);
  $height = imagesy($source_image);
  /* find the "desired height" of this thumbnail, relative to the desired width */
  $desired_height = floor($height*($desired_width/$width));
  /* create a new, "virtual" image */
  $virtual_image = imagecreatetruecolor($desired_width,$desired_height);
  /* copy source image at a resized size */
  imagecopyresized($virtual_image,$source_image,0,0,0,0,$desired_width,$desired_height,$width,$height);
  /* create the physical thumbnail image to its destination */
  imagejpeg($virtual_image,$dest, 83);
}

<?php
/*
*@im //需要缩放的图片资源
*@filetype //制作的缩略图文件类型
*@dstimW   //缩放的图片的宽度
*@dstimH  //缩放的图片的高度
*@thumbname //缩略图文件名字
function makethumb($im,$dstimW,$dstimH,$thumbname ,$filetype){
//获取im的宽度和高度
$pic_W=imagesx($im);
$pic_H=imagesy($im);
$arr = array();
swith($filetype){
case 'jpg':
$arr[$filetype]="imagejpeg";
break;
case 'png';
$arr[$filetype]="imagepng";
break;
case 'jif';
$arr[$filetype]="imagegif";
}
if(($dstimgW && $dstimgW<$pic_W) || ($dstimgH && $dstimgH<$pic_H) ){
if($dstimgW && $dstimgW<$pic_W){
$dsimgWratio = $dstimgW / $pic_w;
$resizereagW =true;
}
if($dstimgH && $ $dstimgH <$pic_H){
$dsimgHratio = $dstimgH/$pic_H;
$resizerreagH =true;
}
//缩略图宽高和原图宽高比，取最小的那个
if($resizereagW && $resizerreagH){
if($dsimgWratio<$dsimgHratio)
$radio = $dsimgWratio;
else
$radio = $dsimgHratio; 
} //www.jb200.com
if($resizereagW && !$resizerreagH ){
$radio = $dsimgWratio;
}
if(!$resizereagW && $resizerreagH){
   $radio = $dsimgHratio ;
}
$imgnewW = $pic_W * $radio;
$imgnewH = $pic_H * $radio;
if(function_exists("imgcopyresampled")){
  //创建目标资源画布
$dst = imagecreatetruecolor ($imgnewW, $imgnewH);
imagecopyresampled ($dst,$im,0,0,0,0,$imgnewW,$imgnewH,$pic_W,$pic_H);
}else{
 $dst=imagecreate($imgnewW, $imgnewH);
 imagecopyresized ($dst, $im,0,0,0,0,$imgnewW,$imgnewH,$imgnewH,$pic_W,$pic_H);
}
$arr[$filetype]($dst,$thumbname.".$filetype");
imagedestroy ($dst);
}else{//缩略图自身的宽和高已经大于了原图的宽和高
   //则缩略图的宽和缩略的高就是原图的宽和原图的高
 $arr[$filetype]($im,$thumbname.".$filetype");
 imagedestroy();
}
}
?>