本文介绍了关于PHP解决图片无损压缩的问题，分享给大家，具体如下：
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;
}
?>
