can not see disparity image using two usb camera with stereo_view node

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Hi,

I am using two usb cameras to use them as a stereo camera. I have calibrated them and left.yaml and right.yaml configuration files have been successfully created. As a next step I want to see the disparity image using the following command

$ROS_NAMESPACE=/stereo rosrun stereo_image_proc stereo_image_proc

In another terminal by typing $rostopic list I can see the relevant rostopics those are required to use to see disparity image with stereo_view node. I can see the rectified color images correctly from both the cameras by typing the following in the terminal,

$rosrun image_view image_view image:=/stereo/left/image_rect_color
$rosrun image_view image_view image:=/stereo/right/image_rect_color

After that in another terminal I type the following to see the disparity image,

$rosrun image_view stereo_view stereo:=/stereo image:=image_rect _approximate_sync:=True _queue_size:=10

I am getting the following error after I run the above command,

(disparity:10586): Gtk-ERROR **: GTK+ 2.x symbols detected. Using GTK+ 2.x and GTK+ 3 in the same process is not supported

I get the same error as above if I use the command as below which supposed to display only the disparity image

$rosrun image_view disparity_view image:=/stereo/disparity

I am using Ubuntu 14.04, ROS version is indigo.

Any help is appreciated.