public function countGlobalColors()
    {
        $byte = substr($this->logicalScreenDescriptor, 4, 1);

        if (strlen($byte) == 1) {
            $byte = unpack('C', $byte)[1];
            $bit = $byte & bindec('00000111');
        }
        
        // length of the global color table is 2^(N+1)        
        return isset($bit) ? pow(2, $bit + 1) : 0;
    }
public function countGlobalColors()
    {
        $byte = substr($this->logicalScreenDescriptor, 4, 1);

        if (strlen($byte) == 1) {
            $byte = unpack('C', $byte)[1];
            $bit = $byte & bindec('00000111');
        }
        
        // length of the global color table is 2^(N+1)        
        return isset($bit) ? pow(2, $bit + 1) : 0;
    }
public function countGlobalColors ( ) { $ byte = substr ( $ this -> logicalScreenDescriptor , 4 , 1 ) ; if ( strlen ( $ byte ) == 1 ) { $ byte = unpack ( 'C' , $ byte ) [ 1 ] ; $ bit = $ byte & bindec ( '00000111' ) ; } // length of the global color table is 2^(N+1)         return isset ( $ bit ) ? pow ( 2 , $ bit + 1 ) : 0 ; }
Get number colors in global color palette

@return int
Get number colors in global color palette