image_type_to_mime_type()

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

取得 getimagesize，exif_read_data，exif_thumbnail，exif_imagetype 所返回的图像类型的 MIME 类型

说明

image_type_to_mime_type(int $imagetype): string

image_type_to_mime_type()函数可以判断一个 IMAGETYPE 常量的 MIME 类型。

image_type_to_mime_type(file)

<?php
header("Content-type: " . image_type_to_mime_type(IMAGETYPE_PNG));
?>

返回值如下：

Note:本函数不需要 GD 库。

参见getimagesize()，exif_imagetype()，exif_read_data()和exif_thumbnail()。

If you are working with Images only and you need mime type (e.g. for headers), then this is a fast and reliable technique:
 
<?php
$file = 'path/to/image.jpg';
$image_mime = image_type_to_mime_type(exif_imagetype($file));
?>
It will output true image mime type even if you rename your image file.

I was looking to detect the format of images, Im not sure if this is the best way but it works for me.
<?php
$filename = 'http://static.php.net/www.php.net/images/php.gif';
$size = getimagesize($filename);
switch ($size['mime']) {
  case "image/gif":
    echo "Image is a gif";
    break;
  case "image/jpeg":
    echo "Image is a jpeg";
    break;
  case "image/png":
    echo "Image is a png";
    break;
  case "image/bmp":
    echo "Image is a bmp";
    break;
}
?>

Map the image type enum to file extension:
$extensions = array(
  IMAGETYPE_GIF => "gif",
  IMAGETYPE_JPEG => "jpg",
  IMAGETYPE_PNG => "png",
  IMAGETYPE_SWF => "swf",
  IMAGETYPE_PSD => "psd",
  IMAGETYPE_BMP => "bmp",
  IMAGETYPE_TIFF_II => "tiff",
  IMAGETYPE_TIFF_MM => "tiff",
  IMAGETYPE_JPC => "jpc",
  IMAGETYPE_JP2 => "jp2",
  IMAGETYPE_JPX => "jpx",
  IMAGETYPE_JB2 => "jb2",
  IMAGETYPE_SWC => "swc",
  IMAGETYPE_IFF => "iff",
  IMAGETYPE_WBMP => "wbmp",
  IMAGETYPE_XBM => "xbm",
  IMAGETYPE_ICO => "ico"
);