I want to start opencv with this
tutorial<http://www.ros.org/wiki/cv_bridge/Tutorials/UsingCvBridgeToConvertBetweenROSImagesAndOpenCVImages>but
it doesn't work for me.

I created a new package then added the cpp file to the src folder then added
this line: rosbuild_add_executable(pkg_test0_imgToCv
src/pkg_test0_imgToCv.cpp) to the CMakeLists.txt file. I already added the
dependencies to the manifest file. Then make.

When I run it nothing happens, I expect the highgui would appear. I can
confirm that my camera(gscam) is streaming images. I can see that the topics
listed are active but using echo on the image_topic and image_topic_2 prints
out nothing. Using rxgraph, there are only the gstreamer_publisher node and
image_converter node connected to rosout node. Did I miss something? How do
I get this thing to work?

thanks