Synchronizing two or more image_transport subscriptions

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Hi All,

I wish to be able to take two subscriptions from two image_transports and synchronize them using boost::bind and message_filters::Synchronizer. But message_filters::Synchronizer only uses sensor_msgs::Image and message_filters::Subscriber.

How do I synchronize image_transport and not message_filters::Subscriber ? so that I can finally use the input with cv_bridge to get a cv::Mat .