camera image not received for gscam kind camera in trailnet_debug_gscam.launch/trailnet_debug_zed_gscam.launch

[vxgu86]

when I debug trailnet_debug_gscam.launch/trailnet_debug_zed_gscam.launch in rviz, for gscam kind camera,
the camera part -- image topic shows that image not received, and camera is whole black,
but the real-time camera could be shown in rqt--image window.
below is my param, I did know what is the problem?

<node>   
 <param name="gscam_config" value="v4l2src device=$(arg device) ! video/x-raw, width=$(arg img_width), height=$(arg img_height) ! videoconvert" />
    <param name="frame_id"        value="$(arg frame_id)" /> 
</node>