private function writeHeader($initialFrame)
{
$data = 'GIF89a';
if (ord($initialFrame[10]) & 0x80) {
$cmap = 3 * (2 << (ord($initialFrame[10]) & 0x7));
$data .= substr($initialFrame, 6, 7);
$data .= substr($initialFrame, 13, $cmap);
if ($this->loopCount >= 0) {
$data .= "!ΓΏ\vNETSCAPE2.0" . $this->gifWord($this->loopCount) . "";
}
}
return $data;
}