php 图片格式转换-亲测ok

/**
* 图片格式转换
* @param string $image_path 文件路径或url
* @param string $to_ext 待转格式，支持png,gif,jpeg,wbmp,webp,xbm
* @param null|string $save_path 存储路径，null则返回二进制内容，string则返回true|false
* @return boolean|string $save_path是null则返回二进制内容，是string则返回true|false
* @throws Exception
* @author klinson <klinson@163.com>
*/
function transform_image($image_path, $to_ext = 'png', $save_path = null)
{
if (! in_array($to_ext, ['png', 'gif', 'jpeg', 'wbmp', 'webp', 'xbm'])) {
throw new \Exception('unsupport transform image to ' . $to_ext);
}
switch (exif_imagetype($image_path)) {
case IMAGETYPE_GIF :
$img = imagecreatefromgif($image_path);
break;
case IMAGETYPE_JPEG :
case IMAGETYPE_JPEG2000:
$img = imagecreatefromjpeg($image_path);
break;
case IMAGETYPE_PNG:
$img = imagecreatefrompng($image_path);
break;
case IMAGETYPE_BMP:
case IMAGETYPE_WBMP:
$img = imagecreatefromwbmp($image_path);
break;
case IMAGETYPE_XBM:
$img = imagecreatefromxbm($image_path);
break;
case IMAGETYPE_WEBP: //(从 PHP 7.1.0 开始支持)
$img = imagecreatefromwebp($image_path);
break;
default :
throw new \Exception('Invalid image type');
}
$function = 'image'.$to_ext;
if ($save_path) {
return $function($img, $save_path);
} else {
$tmp = __DIR__.'/'.uniqid().'.'.$to_ext;
if ($function($img, $tmp)) {
$content = file_get_contents($tmp);
unlink($tmp);
return $content;
} else {
unlink($tmp);
throw new \Exception('the file '.$tmp.' can not write');
}
}
}