我有一个代码可以这样做:
switch (strtolower($imgOrginalsize['mime'])) {
case 'image/jpeg':
$img = imagecreatefromjpeg($file);
$new = imagecreatetruecolor($w, $h);
imagecopyresampled($new, $img, 0, 0, 0, 0, $w, $h, $imgOrginalsize[0], $imgOrginalsize[1]);
header('Content-Type: image/jpeg');
imagepng($new, $pathToSave . $file_name, 9);
imagedestroy($new);
break;
case 'image/png':
$img = imagecreatefrompng($file);
$new = imagecreatetruecolor($w, $h);
imagecopyresampled($new, $img, 0, 0, 0, 0, $w, $h, $imgOrginalsize[0], $imgOrginalsize[1]);
header('Content-Type: image/png');
imagepng($new, $pathToSave . $file_name, 9);
imagedestroy($new);
break;
default:
die();
}