usb_cam bring_up (roslaunch with imput arguments)

my_camera.launch

<launch>
  <arg name="foo"/>

  <node name="usb_cam" pkg="usb_cam" type="usb_cam_node"
    output="screen" >
    <param name="video_device" value="/dev/video0" />
    <param name="image_width" value="640" />
    <param name="image_height" value="480" />
    <param name="pixel_format" value="mjpeg" />
    <param name="camera_frame_id" value="usb_cam" />
    <param name="io_method" value="mmap"/>
    <param name="camera_info_url" type="string" value="file://$(find my_camera_launcher)/config/hp.yml" />
  </node>

  <!-- Launching image_view node -->
  <group if="$(arg foo)">
    <node name="image_view" pkg="image_view" type="image_view"
      respawn="false" output="screen">
        <remap from="image" to="/usb_cam/image_raw"/>
        <param name="autosize" value="true" />
      </node>
    </group>
</launch>