php生成缩略图的方法介绍

<?php
// +----------------------------------------------------------------------
// | 把大图缩略到缩略图指定的范围内,可能有留白（原图细节不丢失）
// +---------------------------------------------------------------------- 
$w = $_GET['w']?$_GET['w']:200;
$h = $_GET['h']?$_GET['h']:200;
$filename = "stand_test_".$w."_".$h.".jpg";
image_resize( 'test.jpg',$filename, $w, $h);
header("content-type:image/png");//设定生成图片格式
echo file_get_contents($filename);
 
function image_resize($f, $t, $tw, $th){
// 按指定大小生成缩略图，而且不变形，缩略图函数
 $temp = array(1=>'gif', 2=>'jpeg', 3=>'png');
 
 list($fw, $fh, $tmp) = getimagesize($f);
 
 if(!$temp[$tmp]){
 return false;
 }
 $tmp = $temp[$tmp];
 $infunc = "imagecreatefrom$tmp";
 $outfunc = "image$tmp";
 
 $fimg = $infunc($f);
 
 // 使缩略后的图片不变形，并且在 缩略图宽高范围内
 if($fw/$tw > $fh/$th){
 $th = $tw*($fh/$fw);
 }else{
 $tw = $th*($fw/$fh);
 }
 
 $timg = imagecreatetruecolor($tw, $th);
 imagecopyresampled($timg, $fimg, 0,0, 0,0, $tw,$th, $fw,$fh);
 if($outfunc($timg, $t)){
 return true;
 }else{
 return false;
 }
}
?>

<?php
// +----------------------------------------------------------------------
// | 把大图缩略到缩略图指定的范围内，不留白（原图会居中缩放，把超出的部分裁剪掉）
// +----------------------------------------------------------------------
$w = $_GET['w']?$_GET['w']:200;
$h = $_GET['h']?$_GET['h']:200;
$filename = "cut_test_".$w."_".$h.".jpg";
image_resize( 'test.jpg',$filename, $w, $h);
header("content-type:image/png");//设定生成图片格式
echo file_get_contents($filename);
 
// 按指定大小生成缩略图，而且不变形，缩略图函数
function image_resize($f, $t, $tw, $th){
 $temp = array(1=>'gif', 2=>'jpeg', 3=>'png');
 list($fw, $fh, $tmp) = getimagesize($f);
 if(!$temp[$tmp]){
 return false;
 }
 $tmp = $temp[$tmp];
 $infunc = "imagecreatefrom$tmp";
 $outfunc = "image$tmp";
 
 $fimg = $infunc($f);
// $fw = 10;
// $fh = 4;
// $tw = 4;
// $th = 2;
 // 把图片铺满要缩放的区域
 if($fw/$tw > $fh/$th){
 $zh = $th;
 $zw = $zh*($fw/$fh);
 $_zw = ($zw-$tw)/2;
 }else{
 $zw = $tw;
 $zh = $zw*($fh/$fw);
 $_zh = ($zh-$th)/2;
 }
// echo $zw."<br>"; 
// echo $zh."<br>"; 
// echo $_zw."<br>"; 
// echo $_zh."<br>"; 
// exit;
 $zimg = imagecreatetruecolor($zw, $zh);
 // 先把图像放满区域
 imagecopyresampled($zimg, $fimg, 0,0, 0,0, $zw,$zh, $fw,$fh);
 
 // 再截取到指定的宽高度
 $timg = imagecreatetruecolor($tw, $th);
 imagecopyresampled($timg, $zimg, 0,0, 0+$_zw,0+$_zh, $tw,$th, $zw-$_zw*2,$zh-$_zh*2);
// 
 if($outfunc($timg, $t)){
 return true;
 }else{
 return false;
 }
}
 
?>

<?php
// +----------------------------------------------------------------------
// | 把大图缩略到缩略图指定的范围内，不留白（原图会剪切掉不符合比例的右边和下边）
// +----------------------------------------------------------------------
$w = $_GET['w']?$_GET['w']:200;
$h = $_GET['h']?$_GET['h']:200;
$filename = "strict_test_".$w."_".$h.".jpg";
image_resize( 'test.jpg',$filename, $w, $h);
header("content-type:image/png");//设定生成图片格式
echo file_get_contents($filename);
 
function image_resize($f, $t, $tw, $th){
// 按指定大小生成缩略图，而且不变形，缩略图函数
 $temp = array(1=>'gif', 2=>'jpeg', 3=>'png');
 
 list($fw, $fh, $tmp) = getimagesize($f);
 
 if(!$temp[$tmp]){
 return false;
 }
 $tmp = $temp[$tmp];
 $infunc = "imagecreatefrom$tmp";
 $outfunc = "image$tmp";
 
 $fimg = $infunc($f);
 
 if($fw/$tw > $fh/$th){
 $fw = $tw * ($fh/$th);
 }else{
 $fh = $th * ($fw/$tw);
 }
 
 $timg = imagecreatetruecolor($tw, $th);
 imagecopyresampled($timg, $fimg, 0,0, 0,0, $tw,$th, $fw,$fh);
 if($outfunc($timg, $t)){
 return true;
 }else{
 return false;
 }
}
?>