exif_imagetype()

(PHP 4 >= 4.3.0, PHP 5, PHP 7)

判断一个图像的类型

说明

exif_imagetype(string $filename): int

exif_imagetype()读取一个图像的第一个字节并检查其签名。

本函数可用来避免调用其它exif函数用到了不支持的文件类型上或和$_SERVER['HTTP_ACCEPT']结合使用来检查浏览器是否可以显示某个指定的图像。

参数

$filename

被检查的图像文件名。

返回值

如果发现了恰当的签名则返回一个对应的常量，否则返回FALSE。返回值和getimagesize()返回的数组中的索引 2 的值是一样的，但本函数快得多。

更新日志

预定义常量

定义有以下常量，并代表了exif_imagetype()可能的返回值：

范例

exif_imagetype()例子

<?php
if (exif_imagetype("image.gif") != IMAGETYPE_GIF) {
    echo "The picture is not a gif";
}
?>

参见

• getimagesize()取得图像大小

Because I only want to check for jpeg or png from a memory string, this is my 2 functions that are quick and don't have any dependencies :
<?php
 function is_jpeg(&$pict)
 {
  return (bin2hex($pict[0]) == 'ff' && bin2hex($pict[1]) == 'd8');
 }
 function is_png(&$pict)
 {
  return (bin2hex($pict[0]) == '89' && $pict[1] == 'P' && $pict[2] == 'N' && $pict[3] == 'G');
 }
?>

By trial and error, it seems that a file has to be 12 bytes or larger in order to avoid a "Read error!". Here's a work-around to avoid an error being thrown:
// exif_imagetype throws "Read error!" if file is too small
if (filesize($uploadfile) > 11)
  $mimetype = exif_imagetype($uploadfile);
else
  $mimetype = false;

Windows users: If you get the fatal error "Fatal error: Call to undefined function exif_imagetype()", and you have enabled php_exif.dll, make sure you enable php_mbstring.dll. You must put mbstring before exif in the php.ini, i.e.:
extension=php_mbstring.dll
extension=php_exif.dll
You can check whether this has worked by calling phpinfo() and searching for exif.

If the function exif_imagetype() is not available,
you can try the following workaround:
if ( ! function_exists( 'exif_imagetype' ) ) {
  function exif_imagetype ( $filename ) {
    if ( ( list($width, $height, $type, $attr) = getimagesize( $filename ) ) !== false ) {
      return $type;
    }
  return false;
  }
}

to checking file is image, I used this:
function is_image($path)
{
  $a = getimagesize($path);
  $image_type = $a[2];
  if(in_array($image_type , array(IMAGETYPE_GIF , IMAGETYPE_JPEG ,IMAGETYPE_PNG , IMAGETYPE_BMP)))
  {
    return true;
  }
  return false;
}

Seems to give a 'Read error' warning if the size of the file is very small (2 bytes). I think this is because it needs a min 3 bytes to determine the file type

libexif can also be used to parse image info out of id3 tags:
exif_read_data("mp3_with_2.4ID3TAGS, '', true, false);