libuvc iris and exposure have no effect

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Hello folks,

I am using libuvc paired with a Logitech C270 camera for some vision processing. I need to change exposure and iris parameters in order to reduce over-exposure.

I've got the suggested launch file from here and changed the auto_exposure to 0. This produced a constant image on the camera. But, changing exposure_absolute and iris_absolute produced no effect on the viewed image. Also, I have no errors while running

Here is my launch file:

<launch>
  <group ns="camera">
    <node pkg="libuvc_camera" type="camera_node" name="mycam">
      <!-- Parameters used to find the camera -->
      <param name="vendor" value="0x046d"/>
      <param name="product" value="0x0825"/>
      <param name="serial" value=""/>
      <!-- If the above parameters aren't unique, choose the first match: -->
      <param name="index" value="0"/>

      <!-- Image size and type -->
      <param name="width" value="640"/>
      <param name="height" value="480"/>
      <!-- choose whichever uncompressed format the camera supports: -->
      <param name="video_mode" value="uncompressed"/> <!-- or yuyv/nv12/jpeg -->
      <param name="frame_rate" value="30"/>

      <param name="timestamp_method" value="start"/> <!-- start of frame -->
      <param name="camera_info_url" value="file:///home/roque/ROS/cal.yml"/>

      <param name="auto_exposure" value="3"/> <!-- use aperture_priority auto exposure -->
      <param name="auto_white_balance" value="false"/>
      <param name="auto_focus" value="false" />
      <param name="auto_hue" value="false"/>

      <param name="exposure_absolute" value="0.01"/>
      <param name="iris_absolute" value="1" />
      <param name="focus_absolute" value="1"/>
      <param name="brightness" value="1000"/>
      <param name="contrast" value="0"/>
      <param name="gain" value="0"/>
      <param name="saturation" value="0"/>
      <param name="sharpness" value="0"/>
    </node>
    <node name="image_view" pkg="image_view" type="image_view" respawn="false" output="screen">
      <remap from="image" to="/camera/image_raw"/>
      <param name="autosize" value="true" />
    </node>
  </group>
</launch>

Thank you in advance!

With my best regards,

Pedro