php图片压缩不失真的实现方法：首先设置图片压缩比；然后通过“getimagesize”函数获取原图尺寸；最后使用“imagecopyresampled”函数压缩图片即可。

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PHP解决图片无损压缩

代码如下：

header("Content-type: image/jpeg");
$file = "111.jpg";
$percent = 1.5; //图片压缩比
list($width, $height) = getimagesize($file); //获取原图尺寸
//缩放尺寸
$newwidth = $width * $percent;
$newheight = $height * $percent;
$src_im = imagecreatefromjpeg($file);
$dst_im = imagecreatetruecolor($newwidth, $newheight);
imagecopyresized($dst_im, $src_im, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);
imagejpeg($dst_im); //输出压缩后的图片
imagedestroy($dst_im);
imagedestroy($src_im);

我发现用php的imagecopyresized把大图片缩成小图片时，图片会变得很模糊，这时候要提升清晰度不如用 imagecopyresampled 代替 imagecopyresized也许会更好。

注：压缩有损失是必然的，看的清楚与否实际上就是是否接受这个范围的问题.比如你图像上原图有些点是2px,但是你压缩5倍，那么这些点就会消失。

<?php 
/** 
* desription 压缩图片 
* @param sting $imgsrc 图片路径 
* @param string $imgdst 压缩后保存路径 
*/
function image_png_size_add($imgsrc,$imgdst){ 
 list($width,$height,$type)=getimagesize($imgsrc); 
 $new_width = ($width>600?600:$width)*0.9; 
 $new_height =($height>600?600:$height)*0.9; 
 switch($type){ 
 case 1: 
 $giftype=check_gifcartoon($imgsrc); 
 if($giftype){ 
 header('Content-Type:image/gif'); 
 $image_wp=imagecreatetruecolor($new_width, $new_height); 
 $image = imagecreatefromgif($imgsrc); 
 imagecopyresampled($image_wp, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height); 
 imagejpeg($image_wp, $imgdst,75); 
 imagedestroy($image_wp); 
 } 
 break; 
 case 2: 
 header('Content-Type:image/jpeg'); 
 $image_wp=imagecreatetruecolor($new_width, $new_height); 
 $image = imagecreatefromjpeg($imgsrc); 
 imagecopyresampled($image_wp, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height); 
 imagejpeg($image_wp, $imgdst,75); 
 imagedestroy($image_wp); 
 break; 
 case 3: 
 header('Content-Type:image/png'); 
 $image_wp=imagecreatetruecolor($new_width, $new_height); 
 $image = imagecreatefrompng($imgsrc); 
 imagecopyresampled($image_wp, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height); 
 imagejpeg($image_wp, $imgdst,75); 
 imagedestroy($image_wp); 
 break; 
 } 
} 
/** 
* desription 判断是否gif动画 
* @param sting $image_file图片路径 
* @return boolean t 是 f 否 
*/
function check_gifcartoon($image_file){ 
 $fp = fopen($image_file,'rb'); 
 $image_head = fread($fp,1024); 
 fclose($fp); 
 return preg_match("/".chr(0x21).chr(0xff).chr(0x0b).'NETSCAPE2.0'."/",$image_head)?false:true; 
} 
?>