支持文件上传兼容性好图片缩略图程序

下面提供三款生成缩代码，兼容性都相当的不错，也可以自定高度与宽度哦。

function imageresize($srcfile,$tow,$toh,$tofile="")
{
if($tofile==""){ $tofile = $srcfile; }
$info = "";
$data = getimagesize($srcfile,$info);
switch ($data[2])
{
case 1:
if(!function_exists("imagecreatefromgif")){
echo "你的gd库不能使用gif格式的图片，请使用jpeg或png格式！<a href='网页特效:go(-1);'>返回</a>";
exit();
}
$im = imagecreatefromgif($srcfile);
break;
case 2:
if(!function_exists("imagecreatefromjpeg")){
echo "你的gd库不能使用jpeg格式的图片，请使用其它格式的图片！<a href='javascript:go(-1);'>返回</a>";
exit();
}
$im = imagecreatefromjpeg($srcfile);
break;
case 3:
$im = imagecreatefrompng($srcfile);
break;
}
$srcw=imagesx($im);
$srch=imagesy($im);
$towh=$tow/$toh;
$srcwh=$srcw/$srch;
if($towh<=$srcwh){
$ftow=$tow;
$ftoh=$ftow*($srch/$srcw);
}
else{
$ftoh=$toh;
$ftow=$ftoh*($srcw/$srch);
}
if($srcw>$tow||$srch>$toh)
{
if(function_exists("imagecreatetruecolor")){
@$ni = imagecreatetruecolor($ftow,$ftoh);
if($ni) imagecopyresampled($ni,$im,0,0,0,0,$ftow,$ftoh,$srcw,$srch);
else{
$ni=imagecreate($ftow,$ftoh);
imagecopyresized($ni,$im,0,0,0,0,$ftow,$ftoh,$srcw,$srch);
}
}else{
$ni=imagecreate($ftow,$ftoh);
imagecopyresized($ni,$im,0,0,0,0,$ftow,$ftoh,$srcw,$srch);
}
if(function_exists('imagejpeg')) imagejpeg($ni,$tofile);
else imagepng($ni,$tofile);
imagedestroy($ni);
}
imagedestroy($im);
}

实例代码二

<?php教程
/*构造函数-生成缩略图+水印,参数说明:
$srcfile-图片文件名,
$dstfile-另存文件名,
$markwords-水印文字,
$markimage-水印图片,
$dstw-图片保存宽度,
$dsth-图片保存高度,
$rate-图片保存品质*/
makethumb("a.jpg","b.jpg","50","50");
function makethumb($srcfile,$dstfile,$dstw,$dsth,$rate=100,$markwords=null,$markimage=null)
{
$data = getimagesize($srcfile);
switch($data[2])
{
case 1:
$im=@imagecreatefromgif($srcfile);
break;
case 2:
$im=@imagecreatefromjpeg($srcfile);
break;
case 3:
$im=@imagecreatefrompng($srcfile);
break;
}
if(!$im) return false;
$srcw=imagesx($im);
$srch=imagesy($im);
$dstx=0;
$dsty=0;
if ($srcw*$dsth>$srch*$dstw)
{
$fdsth = round($srch*$dstw/$srcw);
$dsty = floor(($dsth-$fdsth)/2);
$fdstw = $dstw;
}
else
{
$fdstw = round($srcw*$dsth/$srch);
$dstx = floor(($dstw-$fdstw)/2);
$fdsth = $dsth;
}
$ni=imagecreatetruecolor($dstw,$dsth);
$dstx=($dstx<0)?0:$dstx;
$dsty=($dstx<0)?0:$dsty;
$dstx=($dstx>($dstw/2))?floor($dstw/2):$dstx;
$dsty=($dsty>($dsth/2))?floor($dsth/s):$dsty;
$white = imagecolorallocate($ni,255,255,255);
$black = imagecolorallocate($ni,0,0,0);
imagefilledrectangle($ni,0,0,$dstw,$dsth,$white);// 填充背景色
imagecopyresized($ni,$im,$dstx,$dsty,0,0,$fdstw,$fdsth,$srcw,$srch);
if($markwords!=null)
{
$markwords=iconv("gb2312","utf-8",$markwords);
//转换文字编码
imagettftext($ni,20,30,450,560,$black,"simhei.ttf",$markwords); //写入文字水印
//参数依次为，文字大小|偏转度|横坐标|纵坐标|文字颜色|文字类型|文字内容
}
elseif($markimage!=null)
{
$wimage_data = getimagesize($markimage);
switch($wimage_data[2])
{
case 1:
$wimage=@imagecreatefromgif($markimage);
break;
case 2:
$wimage=@imagecreatefromjpeg($markimage);
break;
case 3:
$wimage=@imagecreatefrompng($markimage);
break;
}
imagecopy($ni,$wimage,500,560,0,0,88,31); //写入图片水印,水印图片大小默认为88*31
imagedestroy($wimage);
}
imagejpeg($ni,$dstfile,$rate);
imagejpeg($ni,$srcfile,$rate);
imagedestroy($im);
imagedestroy($ni);
}
?>

支持图片上传代码

<?php

 $pic_name=date("dmyhis");

 // 生成图片的宽度
 $pic_width=$_post['width'];

 // 生成图片的高度
 $pic_height=$_post['length'];

 function resizeimage($im,$maxwidth,$maxheight,$name){
  //取得当前图片大小
  $width = imagesx($im);
  $height = imagesy($im);
  //生成缩略图的大小
  if(($width > $maxwidth) || ($height > $maxheight)){
   $widthratio = $maxwidth/$width;  
   $heightratio = $maxheight/$height; 
   if($widthratio < $heightratio){
    $ratio = $widthratio;
   }else{
    $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,$name . ".jpg");
   imagedestroy ($newim);
  }else{
   imagejpeg ($im,$name . ".jpg");
  }
 }

 if($_files['image']['size']){
  //echo $_files['image']['type'];
  if($_files['image']['type'] == "image/pjpeg"||$_files['image']['type'] == "image/jpg"||$_files['image']['type'] == "image/jpeg"){
   $im = imagecreatefromjpeg($_files['image']['tmp_name']);
  }elseif($_files['image']['type'] == "image/x-png"){
   $im = imagecreatefrompng($_files['image']['tmp_name']);
  }elseif($_files['image']['type'] == "image/gif"){
   $im = imagecreatefromgif($_files['image']['tmp_name']);
  }
  if($im){
   if(file_exists($pic_name.'.jpg')){
    unlink($pic_name.'.jpg');
   }
   resizeimage($im,$pic_width,$pic_height,$pic_name);
   imagedestroy ($im);
  }
 }
?>

<img src="<? echo $pic_name.'.jpg'; ?>"><br><br>
<form enctype="multipart/form-data" method="post" action="small_picture.php">
<br>
<input type="file" name="image" size="50" value="浏览"><p>
生成缩略图宽度：<input type="text" name="width" size="5"><p>
生成缩略图长度：<input type="text" name="length" size="5"><p>
<input type="submit" value="上传图片">
</form>

图片按在比较进行放大缩小，这得利用php教程 gd库的函数现实现，我们会利用到imagecreatetruecolor(),imagecopyresampled()来操作

function my_image_resize($src_file, $dst_file, $dst_width=32, $dst_height=32) {
    if($dst_width <1 || $dst_height <1) {
        echo "params width or height error !";
        exit();
    }
    if(!file_exists($src_file)) {
        echo $src_file . " is not exists !";
        exit();
    }

    $type=exif_imagetype($src_file);
    $support_type=array(imagetype_jpeg , imagetype_png , imagetype_gif);

    if(!in_array($type, $support_type,true)) {
        echo "this type of image does not support! only support jpg , gif or png";
        exit();
    }

    switch($type) {
        case imagetype_jpeg :
            $src_img=imagecreatefromjpeg($src_file);
            break;
        case imagetype_png :
            $src_img=imagecreatefrompng($src_file);        
            break;
        case imagetype_gif :
            $src_img=imagecreatefromgif($src_file);
            break;
        default:
            echo "load image error!";
            exit();
    }
    $src_w=imagesx($src_img);
    $src_h=imagesy($src_img);
    $ratio_w=1.0 * $dst_width/$src_w;
    $ratio_h=1.0 * $dst_height/$src_h;
    if ($src_w<=$dst_width && $src_h<=$dst_height) {
        $x = ($dst_width-$src_w)/2;
        $y = ($dst_height-$src_h)/2;
        $new_img=imagecreatetruecolor($dst_width,$dst_height);
        imagecopy($new_img,$src_img,$x,$y,0,0,$dst_width,$dst_height);
        switch($type) {
            case imagetype_jpeg :
                imagejpeg($new_img,$dst_file,100);
                break;
            case imagetype_png :
                imagepng($new_img,$dst_file);
                break;
            case imagetype_gif :
                imagegif($new_img,$dst_file);
                break;
            default:
                break;
        }
    } else {
        $dstwh = $dst_width/$dst_height;
        $srcwh = $src_w/$src_h;
        if ($ratio_w <= $ratio_h) {
            $zoom_w = $dst_width;
            $zoom_h = $zoom_w*($src_h/$src_w);
        } else {
            $zoom_h = $dst_height;
            $zoom_w = $zoom_h*($src_w/$src_h);
        }

        $zoom_img=imagecreatetruecolor($zoom_w, $zoom_h);
        imagecopyresampled($zoom_img,$src_img,0,0,0,0,$zoom_w,$zoom_h,$src_w,$src_h);
        $new_img=imagecreatetruecolor($dst_width,$dst_height);
        $x = ($dst_width-$zoom_w)/2;
        $y = ($dst_height-$zoom_h)/2+1;
        imagecopy($new_img,$zoom_img,$x,$y,0,0,$dst_width,$dst_height);
        switch($type) {
            case imagetype_jpeg :
                imagejpeg($new_img,$dst_file,100);
                break;
            case imagetype_png :
                imagepng($new_img,$dst_file);
                break;
            case imagetype_gif :
                imagegif($new_img,$dst_file);
                break;
            default:
                break;
        }
    }
}

总结，我们要生成比例生成小图就利用$dstwh = $dst_width/$dst_height;
        $srcwh = $src_w/$src_h;进行判断，然后再生成。

class securecode
{
    private static $instance=null;
    private $code = '';
    private $fontfile;
    private $validate;
    private $image;
    private $specialadd = 'special string for securecode';
    private $codeexpire=86400;
    private $codecookiename='secure_code';

    /**
     * 构造方法
     */
    private function securecode()
    {
        $this->fontfile = dirname( __file__ ) . '/arial.ttf';
    }

    private function __construct()
    {
        $this->securecode();
    }
   
    public static function getinstance()
    {
        if (self::$instance==null)
            self::$instance=new self();
       
        return self::$instance;
    }

    /**
     * 指定字体文件所在路径，默认为当前文件夹下arial.ttf文件
     * @param $fontfile 文件路径
     * @return void
     */
    function loadfont($fontfile)
    {
        $this->fontfile = $fontfile;
    }

    /**
     * 图片输出方法，在执行本方法前程序不应该有任何形式的输出
     * @return void;
     */
    function stroke()
    {
        $this->savecode();
        self::sendheader();
        imagegif( $this->validate );
        imagedestroy( $this->validate );
        imagedestroy( $this->image );
    }

    /**
     * 图片保存方法
     * @param $filename 保存路径
     * @return void
     */
    function save($filename)
    {
        $this->savecode();
        imagegif( $this->validate , $filename );
        imagedestroy( $this->validate );
        imagedestroy( $this->image );
    }
   
  /**
     * 验证码验证方法
     * @param $input 要验证的字符串，即用户的输入内容
     * @return boolean 验证结果
     */
    function verify($input)
    {
        $input=strtolower($input);
        $targetcode=$this->authcode($input);
        $code=$this->getcookie();
        if (empty($code)||$code!=$targetcode)
            $result= false;
        else
            $result=true;
        $_cookie[$this->codecookiename]='';
        setcookie ( $this->codecookiename, '', - 1 );
        return $result;
    }

    /**
     * 图片创建方法
     * @return void;
     */
    function createimage()
    {
        $this->randcode();
       
        $size = 30;
        $width = 90;
        $height = 35;
        $degrees = array (
            rand( 0 , 30 ), rand( 0 , 30 ), rand( 0 , 30 ), rand( 0 , 30 )
        );
       

        for ($i = 0; $i < 4; ++$i)
        {
            if (rand() % 2);
            else $degrees[$i] = -$degrees[$i];
        }
       
        $this->image = imagecreatetruecolor( $size , $size );
        $this->validate = imagecreatetruecolor( $width , $height );
        $back = imagecolorallocate( $this->image , 255 , 255 , 255 );
        $border = imagecolorallocate( $this->image , 0 , 0 , 0 );
        imagefilledrectangle( $this->validate , 0 , 0 , $width , $height , $back );
       
        for ($i = 0; $i < 4; ++$i)
        {
            $temp = self::rgbtohsv( rand( 0 , 250 ) , rand( 0 , 150 ) , rand( 0 , 250 ) );
           
            if ($temp[2] > 60) $temp[2] = 60;
           
            $temp = self::hsvtorgb( $temp[0] , $temp[1] , $temp[2] );
            $textcolor[$i] = imagecolorallocate( $this->image , $temp[0] , $temp[1] , $temp[2] );
        }
       
        for ($i = 0; $i < 200; ++$i)
        {
            $randpixelcolor = imagecolorallocate( $this->validate , rand( 0 , 255 ) , rand( 0 , 255 ) , rand( 0 , 255 ) );
            imagesetpixel( $this->validate , rand( 1 , 87 ) , rand( 1 , 35 ) , $randpixelcolor );
        }
       
        $temp = self::rgbtohsv( rand( 220 , 255 ) , rand( 220 , 255 ) , rand( 220 , 255 ) );
       
        if ($temp[2] < 200) $temp[2] = 255;
       
        $temp = self::hsvtorgb( $temp[0] , $temp[1] , $temp[2] );
        $randlinecolor = imagecolorallocate( $this->image , $temp[0] , $temp[1] , $temp[2] );
       
        self::imagelinethick( $this->validate , $textcolor[rand( 0 , 3 )] );
       
        imagefilledrectangle( $this->image , 0 , 0 , $size , $size , $back );
        putenv( 'gdfontpath=' . realpath( '.' ) );
       
        // name the font to be used (note the lack of the .ttf extension
        imagettftext( $this->image , 15 , 0 , 8 , 20 , $textcolor[0] , $this->fontfile , $this->code[0] );
       
        $this->image = imagerotate( $this->image , $degrees[0] , $back );
        imagecolortransparent( $this->image , $back );
        imagecopymerge( $this->validate , $this->image , 1 , 4 , 4 , 5 , imagesx( $this->image ) - 10 , imagesy( $this->image ) - 10 , 100 );
       
        $this->image = imagecreatetruecolor( $size , $size );
        imagefilledrectangle( $this->image , 0 , 0 , $size , $size , $back );
        imagettftext( $this->image , 15 , 0 , 8 , 20 , $textcolor[1] , $this->fontfile , $this->code[1] );
        $this->image = imagerotate( $this->image , $degrees[1] , $back );
        imagecolortransparent( $this->image , $back );
        imagecopymerge( $this->validate , $this->image , 21 , 4 , 4 , 5 , imagesx( $this->image ) - 10 , imagesy( $this->image ) - 10 , 100 );
       
        $this->image = imagecreatetruecolor( $size , $size );
        imagefilledrectangle( $this->image , 0 , 0 , $size - 1 , $size - 1 , $back );
        imagettftext( $this->image , 15 , 0 , 8 , 20 , $textcolor[2] , $this->fontfile , $this->code[2] );
        $this->image = imagerotate( $this->image , $degrees[2] , $back );
        imagecolortransparent( $this->image , $back );
        imagecopymerge( $this->validate , $this->image , 41 , 4 , 4 , 5 , imagesx( $this->image ) - 10 , imagesy( $this->image ) - 10 , 100 );
       
        $this->image = imagecreatetruecolor( $size , $size );
        imagefilledrectangle( $this->image , 0 , 0 , $size - 1 , $size - 1 , $back );
        imagettftext( $this->image , 15 , 0 , 8 , 20 , $textcolor[3] , $this->fontfile , $this->code[3] );
        $this->image = imagerotate( $this->image , $degrees[3] , $back );
        imagecolortransparent( $this->image , $back );
        imagecopymerge( $this->validate , $this->image , 61 , 4 , 4 , 5 , imagesx( $this->image ) - 10 , imagesy( $this->image ) - 10 , 100 );
        imagerectangle( $this->validate , 0 , 0 , $width - 1 , $height - 1 , $border );
    }
   
    /**
     * 获取随机生成的验证码
     * @return string 随机验证码，返回的验证码不进行任何处理
     */
    function getcode()
    {
        return $this->code;
    }

    /**
     * 生成随机码方法
     * @return void;
     */
    protected function randcode()
    {
        $alphastr = 'abcdefghijklmnpqrstuvwxyz123456789';
        $randstr = array (
            $alphastr{rand( 0 , 33 )}, $alphastr{rand( 0 , 33 )}, $alphastr{rand( 0 , 33 )}, $alphastr{rand( 0 , 33 )}
        );
        $this->code = strtolower( $randstr[0] . $randstr[1] . $randstr[2] . $randstr[3] );
    }

    /**
     * rgb色到hsv色转变方法
     * @param $r
     * @param $g
     * @param $b
     * @return array hsv数组
     */
    protected static function rgbtohsv($r, $g, $b)
    {
        $tmp = min( $r , $g );
        $min = min( $tmp , $b );
        $tmp = max( $r , $g );
        $max = max( $tmp , $b );
        $v = $max;
        $delta = $max - $min;
       
        if ($max != 0) $s = $delta / $max; // s
        else
        {
            $s = 0;
            //$h = undefinedcolor;
            return;
        }
        if ($r == $max) $h = ($g - $b) / $delta; // between yellow & magenta
        else if ($g == $max) $h = 2 + ($b - $r) / $delta; // between cyan & yellow
        else $h = 4 + ($r - $g) / $delta; // between magenta & cyan
       

        $h *= 60; // degrees
        if ($h < 0) $h += 360;
        return array (
            $h, $s, $v
        );
    }

    /**
     * 同上一方法功能相反
     * @param $h
     * @param $s
     * @param $v
     * @return array rgb数组
     */
    protected static function hsvtorgb($h, $s, $v)
    {
        if ($s == 0)
        {
            // achromatic (grey)
            $r = $g = $b = $v;
            return;
        }
       
        $h /= 60; // sector 0 to 5
        $i = floor( $h );
        $f = $h - $i; // factorial part of h
        $p = $v * (1 - $s);
        $q = $v * (1 - $s * $f);
        $t = $v * (1 - $s * (1 - $f));
       
        switch ($i)
        {
            case 0 :
                $r = $v;
                $g = $t;
                $b = $p;
                break;
            case 1 :
                $r = $q;
                $g = $v;
                $b = $p;
                break;
            case 2 :
                $r = $p;
                $g = $v;
                $b = $t;
                break;
            case 3 :
                $r = $p;
                $g = $q;
                $b = $v;
                break;
            case 4 :
                $r = $t;
                $g = $p;
                $b = $v;
                break;
            default : // case 5:
                $r = $v;
                $g = $p;
                $b = $q;
                break;
        }
        return array (
            $r, $g, $b
        );
    }

    /**
     * 使用cookie保存验证码的方法
     * @return void
     */
    protected function savecode()
    {
        $code = $this->authcode($this->code);
        $this->setcookie($code);
    }

    /**
     * 验证码cookie值获取方法
     * @return string cookie值
     */
    protected function getcookie()
    {
        if (empty( $_cookie[$this->codecookiename] ))
        {
            return '';
        }
        else
        {
            return addslashes($_cookie[$this->codecookiename]);
        }
    }
   
    /**
     * 验证码cookie创建方法
     * @param string $code 要保存的验证码
     * @return void
     */
    protected function setcookie($code)
    {
        $expire = $this->codeexpire > 0 ? $this->codeexpire + time() : 0;
        setcookie( $this->codecookiename , $code, $expire );
    }
   
    /**
     * 验证码加密方法
     * @param string $code 要加密的随机码
     * @return mixed 执行结果
     */
    protected function authcode($code)
    {
        return md5($code.$this->specialadd);
    }
   
    /**
     * 干扰线生成方法
     * @param resource $image 图片资源句柄
     * @param string $color 干扰线颜色
     */
    protected static function imagelinethick($image, $color)
    {
        $k = rand( 5 , 20 );
        for ($px = 0; $px < 400; $px = $px + 1)
        {
            $y = $k * sin( 0.1 * ($px) ); //$y=200+10*sin(0.1*($px-200));
            for ($i = 0; $i < 2; $i++)
            {
                imagesetpixel( $image , $px , $y + 10 + $i , $color );
            }
       
        }
    }

    /**
     * http标头设置方法
     * @return void
     */
    protected static function sendheader()
    {
        header( "pragma: no-cache" );
        header( "cache-control: max-age=1, s-maxage=1, no-cache, must-revalidate" );
        header( 'content-type: image/gif' );
    }
}
http://down.111cn.net/down/code/php/qitayuanma/2010/1220/22330.html

imagecreatetruecolor（）返回一个图像标识符代表指定大小的黑色形象。

根据你的php教程和gd版本中函数定义与否。对于php 4.0.6通过4.1.x这个函数总是存在的

，
*/
$im=imagecreatetruecolor(100,100);        //创建图像
$string='n';            //定义字符
$white=imagecolorallocate($im,255,255,255);      //定义白色
$black=imagecolorallocate($im,0,0,0);       //定义黑色
$red=imagecolorallocate($im,255,0,0);       //定义红色
//在白色的背景上输出一个黑色的"z"，其实是颠倒的n
imagecharup($im,6,20,20,$string,$white);
imagechar($im,2,40,40,"r",$red);        //使用红色画出字符
header('content-type: image/png');        //输出头部信息
imagepng($im);            //输出png文件
imagedestroy($im);         //销毁图像

//

$img=imagecreatetruecolor(400,400);      //创建图像
$white=imagecolorallocate($img,255,255,255);     //定义白色
$black=imagecolorallocate($img,0,0,0);      //定义黑色
imagearc($img,200,200,350,350,0,360,$white);     //画椭圆弧
header("content-type: image/png");       //输出头信息
imagepng($img);          //输出为png图像
imagedestroy($img);          //销毁图像

//
$size=300;
$image=imagecreatetruecolor($size,$size);
//用白色背景加黑色边框画个方框
$back=imagecolorallocate($image,255,255,255);
$border=imagecolorallocate($image,0,0,0);
imagefilledrectangle($image,0,0,$size-1,$size-1,$back);
imagerectangle($image,0,0,$size-1,$size-1,$border);
$yellow_x=100;
$yellow_y=75;
$red_x=120;
$red_y=165;
$blue_x=187;
$blue_y=125;
$radius=150;
//用alpha值分配一些颜色
$yellow=imagecolorallocatealpha($image,255,255,0,75);
$red=imagecolorallocatealpha($image,255,0,0,75);
$blue=imagecolorallocatealpha($image,0,0,255,75);
//画三个交迭的圆
imagefilledellips教程e($image,$yellow_x,$yellow_y,$radius,$radius,$yellow);
imagefilledellipse($image,$red_x,$red_y,$radius,$radius,$red);
imagefilledellipse($image,$blue_x,$blue_y,$radius,$radius,$blue);
//输出header文件头
header('content-type: image/png');
//最后输出结果
imagepng($image);
imagedestroy($image);

//

$im=imagecreate(100,100);         //创建图像
$string='php';            //定义字符串
$bg=imagecolorallocate($im,255,255,255);      //定义白色
$black=imagecolorallocate($im,0,0,0);       //定义黑色
//在左上角输出指定字符
imagechar($im,1,0,0,$string,$black);
header('content-type: image/png');        //输出头部信息
imagepng($im);            //输出png文件
imagedestroy($im);           //销毁图像

?>

我利用了getimagesize来获取原图片的大小然后再x0.5就是把图片/5哦。

array getimagesize ( string $filename [, array &$imageinfo ] )
getimagesize() 函数将测定任何 gif，jpg，png，swf，swc，ps教程d，tiff，bmp，iff，jp2，jpx，jb2，jpc，xbm 或 wbmp 图像文件的大小并返回图像的尺寸以及文件类型和一个可以用于普通 html 文件中 <img> 标记中的 height/width 文本字符串。
如果不能访问 filename 指定的图像或者其不是有效的图像，getimagesize() 将返回 false 并产生一条 e_warning 级的错误

*/
//定义一个文件
$filename='1.jpg';
$percent=0.5;
//发送头部文件
header('content-type: image/jpeg');
//获取图像的大小
list($width,$height)=getimagesize($filename);
//定义新的大小
$new_width=$width * $percent;
$new_height=$height * $percent;
$image_p=imagecreatetruecolor($new_width, $new_height);
/*
: int imagecreate(int x_size, int y_size);

返回值: 整数

内容说明

本函数用来建立一张全空的图形。参数 x_size、y_size 为图形的尺寸，单位为像素 (pixel)。

*/
$image=imagecreatefromjpeg($filename);

/*
resource imagecreatefromjpeg ( string filename ) 　　imagecreatefromjpeg() 返回一图像标识符，代表了从给定的文件名取得的图像。 　　imagecreatefromjpeg() 在失败时返回一个空字符串，并且输出一条错误信息，不幸地在浏览器中显示为断链接。为减轻调试工作下面的例子会产生一个错误 jpeg：
*/
imagecopyresampled($image_p,$image,0,0,0,0,$new_width,$new_height,$width,$height);

/*
):imagecopyresamples() ,其像素插值算法得到的图像边缘比较平滑.质量较好(但该函数的速度比 imagecopyresized() 慢). 　　两个函数的参数是一样的.如下: 　　imagecopyresampled(dest,src,dx,dy,sx,sy,dw,dh,sw,sh);
*/
//输出图像
imagejpeg($image_p, null, 100);
/*
执行该代码，将把原图像缩放50%，并以新图像输出
*/