Difference between roslaunch and rosrun with image_view

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It's caused by the usage of rosrun:

To set parameters when calling a node with ros run the syntax is:

rosrun package node _parameter:=value

To remap a topic when calling a node with ros run the syntax is:

rosrun package node topic_name:=remapped_topic_name

Note the lack of _ prefix before the topic_name! (See: http://wiki.ros.org/rosbash#rosrun )

Therefore in the example you've given stereo and image are topics and approximate_sync is a parameter. Hence, you cannot set stereo and image as parameters in the roslaunch, you must use the remap tag (See http://wiki.ros.org/roslaunch/XML/remap ). I think the correct launch equivalent would be something like:

<launch>
    <node name="stereo_view" pkg="image_view" type="stereo_view">
        <remap from="stereo" to="raw_stereo" />
        <remap from="image" to="image_rect" />
        <param name="approximate_sync" value="true" />
    </node>
</launch>