Synchronization with 8 incoming channels, registerCallback boost::bind -> compilation error

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Hi all,

UPDATE: I found a workaround which I posted at the end of this question

I try to use ApproximateTime Synchronization with 8 channels, but I get a compilation error. Strangely it works with 4.

Here's some of the code: (The error is at sync_->registerCallback(boost::bind(&S2::filter_image, this, _1, _2, _3, _4, _5, _6, _7, _8, "ok")); )

class S2 {
    ros::NodeHandle nh_;

    image_transport::ImageTransport image_transporter_;
    boost::unordered_map<std::string, boost::shared_ptr<image_transport::SubscriberFilter> > response_; //images from C1

    //Synchronizer
    typedef message_filters::sync_policies::ApproximateTime<sensor_msgs::Image, sensor_msgs::Image,
        sensor_msgs::Image, sensor_msgs::Image,
        sensor_msgs::Image, sensor_msgs::Image,
        sensor_msgs::Image, sensor_msgs::Image> syncPolicy;


    typedef message_filters::Synchronizer<syncPolicy> mySynchronizer;
    boost::shared_ptr<mySynchronizer>  sync_;

public:

    S2(ros::NodeHandle nh): image_transporter_(nh) {
        nh_ = nh;
        read_parameters();
    }

    void read_parameters(){


    //Subscribe to C1 images

            sync_.reset( new mySynchronizer ( syncPolicy(10),
                *C1_response_[subscribe_strings.at(0)].get(),
                *C1_response_[subscribe_strings.at(1)].get(),
                    *C1_response_[subscribe_strings.at(2)].get(),
                    *C1_response_[subscribe_strings.at(3)].get(),
                    *C1_response_[subscribe_strings.at(4)].get(),
                    *C1_response_[subscribe_strings.at(5)].get(),
                    *C1_response_[subscribe_strings.at(6)].get(),
                    *C1_response_[subscribe_strings.at(7)].get()));             
            sync_->registerCallback(boost::bind(&S2::filter_image, this,  _1, _2, _3, _4, _5, _6, _7, _8, "ok"));




    }


    void filter_image(const sensor_msgs::ImageConstPtr& original_image1, const sensor_msgs::ImageConstPtr& original_image2,
            const sensor_msgs::ImageConstPtr& original_image3, const sensor_msgs::ImageConstPtr& original_image4,std::string name){

    }

};

int main(int argc, char **argv){

  ros::init(argc, argv, "S2_node");
  ros::NodeHandle nh;

    S2 s2(nh);
ros::spin();
    return 0;
}

The error I get is:

S2_new_node.cpp: In member function ‘void S2::read_parameters()’:
S2_new_node.cpp:88:102: error: no matching function for call to ‘bind(void (S2::*)(const ImageConstPtr&, const ImageConstPtr&, const ImageConstPtr&, const ImageConstPtr&, std::string), S2* const, boost::arg<1>&, boost::arg<2>&, boost::arg<3>&, boost::arg<4>&, boost::arg<5>&, boost::arg<6>&, boost::arg<7>&, boost::arg<8>&, const char [3])’
/work/ros/hmax/src/S2_new_node.cpp:88:102: note: candidates are:
/usr/include/boost/bind/bind.hpp:1298:5: note: template<class R, class F> boost::_bi::bind_t<R, F, boost::_bi::list0> boost::bind(F)
/usr/include/boost/bind/bind.hpp:1306:5: note: template<class R, class F, class A1> boost::_bi::bind_t<R, F, typename boost::_bi::list_av_1<A1>::type> boost::bind(F, A1)
/usr/include/boost/bind/bind.hpp:1314:5: note: template<class R, class F, class A1, class A2> boost::_bi::bind_t<R, F, typename boost::_bi::list_av_2<A1, A2>::type> boost::bind(F, A1, A2)
/usr/include/boost/bind/bind.hpp:1322:5: note: template<class R, class F, class A1, class A2, class A3> boost::_bi::bind_t<R, F, typename boost::_bi::list_av_3<A1, A2, A3>::type> boost::bind(F, A1, A2, A3)
/usr/include/boost/bind/bind.hpp:1330:5: note: template<class R, class F, class A1, class A2, class A3, class A4> boost::_bi::bind_t<R, F, typename boost::_bi::list_av_4<A1, A2, A3, A4>::type> boost::bind(F, A1, A2, A3, A4)
/usr/include/boost/bind/bind.hpp:1338:5: note: template<class R, class F, class A1, class ...