How does PHP determine if a GIF image is animated?

The first thing to think about is to look at the type with getimagesize () and find it all gif.

Then I think GIF animation is gif89 format, found that the beginning of the file is gif89, but many transparent pictures are also used in the gif89 format.

It seems necessary to analyze the paper. Baidu a bit, found that phpx.com has been resolved.

Description of Dinning:

Check if the file contains

Chr (0x21). chr (0xff). chr (0x0b). NETSCAPE2.0 '

Chr (0x21). Chr (0xff) is the header of an extended segment in a GIF picture

' NETSCAPE2.0 ' is the program name that the extended function executes

Finally, a function is organized:

/* * Determine if the picture is dynamic */function isanimatedgif ($filename) {$fp = fopen ($filename, ' RB '); $filecontent = Fread ($fp, FileSize ($file name); fclose ($fp); return Strpos ($filecontent, Chr (0x21) Chr (0xff). chr (0x0b). ' NETSCAPE2.0 ') = = = FALSE? 0:1;}

How does PHP determine if a GIF image is animated?