Detecting image type from base64 string in PHP
Is it possible to find out the type of an image encoded as a base64 String in PHP?
I have no method of accessing the original image file, just the encoded string. From what I've seen, imagecreatefromstring()
can create an image resource from a string representation (after it's been decoded from base64), but it automatically detects the image type and the image resource itself is a special PHP representation. In case I want to save the image as a file again, I would have no idea if the type I am saving it as corresponds to the original type from which the String representation was created.
FileInfo can do that for you:
$encoded_string = "....";
$imgdata = base64_decode($encoded_string);
$f = finfo_open();
$mime_type = finfo_buffer($f, $imgdata, FILEINFO_MIME_TYPE);
If you dont want to use these functions because of their dependencies you can use the first bytes of the data:
function getBytesFromHexString($hexdata)
{
for($count = 0; $count < strlen($hexdata); $count+=2)
$bytes[] = chr(hexdec(substr($hexdata, $count, 2)));
return implode($bytes);
}
function getImageMimeType($imagedata)
{
$imagemimetypes = array(
"jpeg" => "FFD8",
"png" => "89504E470D0A1A0A",
"gif" => "474946",
"bmp" => "424D",
"tiff" => "4949",
"tiff" => "4D4D"
);
foreach ($imagemimetypes as $mime => $hexbytes)
{
$bytes = getBytesFromHexString($hexbytes);
if (substr($imagedata, 0, strlen($bytes)) == $bytes)
return $mime;
}
return NULL;
}
$encoded_string = "....";
$imgdata = base64_decode($encoded_string);
$mimetype = getImageMimeType($imgdata);