Issue visualizing Depth image in rviz2

[EnzoGhisoni]

Environment

• OS Version: Ubuntu 22.04
• Binary build
• Version: Fortress version 6.16.0 and ROS2 Humble

Description

• Expected behavior:
  I try to add the depth sensors in the sdf of my robot in order to have the depth image available in ROS2.
• Actual behavior:
  I have the good output for the depth image in Gazebo Image display viewer:
  

But when I visualize it in rviz2 the image is fully black or is in reverse color pattern in function of the settings:

Steps to reproduce

I have implement the sensor in this way in my model.sdf:
`

    <sensor name="camera_center" type="depth_camera">
      <gz_frame_id>camera_base_link</gz_frame_id>
      <always_on>1</always_on>
      <update_rate>30</update_rate>
      <visualize>0</visualize>
      <topic>/model/diff_drive/depth_camera</topic>
      <pose>0 0 0 0 -0 0</pose>
      <camera name="camera">
        <horizontal_fov>1</horizontal_fov>
        <image>
          <width>640</width>
          <height>360</height>
          <format>RGB_INT8</format>
        </image>
        <clip>
          <near>0.3</near>
          <far>50.0</far>
        </clip>
      </camera>
  </sensor>

I have this for the bridge:

• ros_topic_name: "/depth"
  gz_topic_name: "/model/diff_drive/depth_camera"
  ros_type_name: "sensor_msgs/msg/Image"
  gz_type_name: "gz.msgs.Image"
  direction: GZ_TO_ROS
  `

I'm not sure if the difference come from the encoding, the bridge or simply the rviz2 configuration (if it is it could be interesting to know the default settings to visualize the data).

[iche033]

I think it's just that the "visualization" is different but the depth image data encoding and depth values should be the same. The image consists of float32 depth values. In gazebo, from this description, large depth values are darker (black) while smaller depth values are brighter (white), which just happens to be opposite of how rviz visualizes depth data.

[azeey]

There doesn't seem to be a standard on how to display depth images. A quick look on the web shows both approaches being used in different places. Since the behavior in Gazebo has been around for a long time, I don't think we should change it. Perhaps a flag in the "Image Display" plugin to revert the colors could be an option.

[azeey]

@EnzoGhisoni I'm going to assign the "help wanted" label to this. If you're able to submit a PR with the suggested changes in #473 (comment), we would greatly appreciate it.