图片品质前后对比 ： var_dump(exif_read_data($img));查看 ，严重失真压缩比为 50%。

压缩前：

array (size=18)

'FileName' => string '1367000585017724053.JPG' (length=23)

'FileDateTime' => int 1367029384

'FileSize' => int 67872

'FileType' => int 2

'MimeType' => string 'image/jpeg' (length=10)

'SectionsFound' => string 'ANY_TAG, IFD0, THUMBNAIL, EXIF' (length=30)

'COMPUTED' =>

array (size=7)

'html' => string 'width="300" height="300"' (length=24)

'Height' => int 300

'Width' => int 300

'IsColor' => int 1

'ByteOrderMotorola' => int 1

'Thumbnail.FileType' => int 2

'Thumbnail.MimeType' => string 'image/jpeg' (length=10)

'Orientation' => int 1

'XResolution' => string '72/1' (length=4)

'YResolution' => string '72/1' (length=4)

'ResolutionUnit' => int 2

'Software' => string 'Adobe Photoshop CS Windows' (length=26)

'DateTime' => string '2013:04:26 10:56:18' (length=19)

'Exif_IFD_Pointer' => int 164

'THUMBNAIL' =>

array (size=6)

'Compression' => int 6

'XResolution' => string '72/1' (length=4)

'YResolution' => string '72/1' (length=4)

'ResolutionUnit' => int 2

'JPEGInterchangeFormat' => int 302

'JPEGInterchangeFormatLength' => int 5519

'ColorSpace' => int 1

'ExifImageWidth' => int 300

'ExifImageLength' => int 300

压缩之后：

array (size=8)

'FileName' => string '1367000585108300044.jpg' (length=23)

'FileDateTime' => int 1367029385

'FileSize' => int 38802

'FileType' => int 2

'MimeType' => string 'image/jpeg' (length=10)

'SectionsFound' => string 'COMMENT' (length=7)

'COMPUTED' =>

array (size=4)

'html' => string 'width="300" height="300"' (length=24)

'Height' => int 300

'Width' => int 300

'IsColor' => int 1

'COMMENT' =>

array (size=1)

0 => string 'CREATOR: gd-jpeg v1.0 (using IJG JPEG v62), quality = 100

' (length=58)

$img_thumb = imagecreatetruecolor($thumb_width, $thumb_height);

$bgcolor = trim($bgcolor,"#");

sscanf($bgcolor, "%2x%2x%2x", $red, $green, $blue);

$clr = imagecolorallocate($img_thumb, $red, $green, $blue);

imagefilledrectangle($img_thumb, 0, 0, $thumb_width, $thumb_height, $clr);

imagecopyresampled($img_thumb, $img_org, $dst_x, $dst_y, 0, 0, $lessen_width, $lessen_height, $org_info[0], $org_info[1]);

图片只要经过那个函数的压缩，仍旧是失真的，图片文件大小压缩率为 50%。