BuddyPress.org

Hi,
How to calculate the avatar filename?
Example : 4ad4e42876148e5930307699dee8bd7f-bpfull.jpg
I read this code
$email = apply_filters( ‘bp_core_gravatar_email’, $email, $item_id, $object );
$gravatar = apply_filters( ‘bp_gravatar_url’, $host ) . md5( strtolower( $email ) ) . ‘?d=’ . $default_grav . ‘&s=’ . $grav_size;

but I have no clue what this first line does.
$email = apply_filters( ‘bp_core_gravatar_email’, $email, $item_id, $object );
Any help?

Regards,