[image_transport] Topics '/usb_cam/image_color' and '/usb_cam/camera_info' do not appear to be synchronized

please help me :( $ rosrun image_transport republish compressed in:=usb_cam/image raw out:=usb_cam/image $ ROS_NAMESPACE=usb_cam rosrun image_proc image_proc image_raw:=image _approximate_s=true _queue_size:=20 [ WARN] [1545066099.656226554]: [image_transport] Topics '/usb_cam/image_color' and '/usb_cam/camera_info' do not appear to be synchronized. In the last 10s: Image messages received: 0 CameraInfo messages received: 45 Synchronized pairs: 0