1. header("Content-type: image/jpeg");
2. $file = "111.jpg";
3. $percent = 1.5; //图片压缩比
4. list($width, $height) = getimagesize($file); //获取原图尺寸
5. //缩放尺寸
6. $newwidth = $width * $percent;
7. $newheight = $height * $percent;
8. $src_im = imagecreatefromjpeg($file);
9. $dst_im = imagecreatetruecolor($newwidth, $newheight);
10. imagecopyresized($dst_im, $src_im, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);
11. imagejpeg($dst_im); //输出压缩后的图片
12. imagedestroy($dst_im);
13. imagedestroy($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。

1. <?php
2. /**
3. * desription 压缩图片
4. * @param sting $imgsrc 图片路径
5. * @param string $imgdst 压缩后保存路径
6. */
7. function image_png_size_add($imgsrc,$imgdst){
8. list($width,$height,$type)=getimagesize($imgsrc);
9. $new_width = ($width>600?600:$width)*0.9;
10. $new_height =($height>600?600:$height)*0.9;
11. switch($type){
12. case 1:
13. $giftype=check_gifcartoon($imgsrc);
14. if($giftype){
15. header('Content-Type:image/gif');
16. $image_wp=imagecreatetruecolor($new_width, $new_height);
17. $image = imagecreatefromgif($imgsrc);
18. imagecopyresampled($image_wp, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height);
19. imagejpeg($image_wp, $imgdst,75);
20. imagedestroy($image_wp);
21. }
22. break;
23. case 2:
24. header('Content-Type:image/jpeg');
25. $image_wp=imagecreatetruecolor($new_width, $new_height);
26. $image = imagecreatefromjpeg($imgsrc);
27. imagecopyresampled($image_wp, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height);
28. imagejpeg($image_wp, $imgdst,75);
29. imagedestroy($image_wp);
30. break;
31. case 3:
32. header('Content-Type:image/png');
33. $image_wp=imagecreatetruecolor($new_width, $new_height);
34. $image = imagecreatefrompng($imgsrc);
35. imagecopyresampled($image_wp, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height);
36. imagejpeg($image_wp, $imgdst,75);
37. imagedestroy($image_wp);
38. break;
39. }
40. }
41. /**
42. * desription 判断是否gif动画
43. * @param sting $image_file图片路径
44. * @return boolean t 是 f 否
45. */
46. function check_gifcartoon($image_file){
47. $fp = fopen($image_file,'rb');
48. $image_head = fread($fp,1024);
49. fclose($fp); //phpfensi.com
50. return preg_match("/".chr(0x21).chr(0xff).chr(0x0b).'NETSCAPE2.0'."/",$image_head)?false:true;
51. }
52. ?>