In Chapter 3, Visualization and Debugging Tools, we explained how to visualize any image published in the ROS framework by using the image_view node of the image_view package or rqt_image_view. The following code encapsulates this discussion:
$ rosrun image_view image_view image:=/camera/image_raw
What is important here is the fact that by using the image transport, we can select different topics for viewing images using compressed formats if required. Also, in the case of stereo vision, as we will see later, we can use rqt rviz to see the point cloud obtained with the disparity image.