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Converting Kinect RGB image to OpenCV gives wrong colours

asked 2011-03-05 02:18:10 -0500

Aslund gravatar image

Hey everyone

I have been playing a bit with the kinect camera using the openni driver. When running openni_node.launch and viewing the rgb image using rviz, then everything looks perfect, but when I create a node that has to the purpose to read the rgb image, convert it to a cv image and displaying it using imshow, then the colours are all wrong. Red is blue, blue is red, green is something yellow and yellow is light blue. I have been trying to use RGB8 and BGR8 encodings, but nether of them shows any difference. A sample of my code is shown below, inspired from the example in the cv_bridge tutorial:

void processRGB::processImage( const sensor_msgs::Image::ConstPtr& img ) {
    CvImagePtr cv_ptr;

    try {

        cv_ptr = toCvCopy(img, enc::BGR8); //enc::RGB8 also used

    } catch (cv_bridge::Exception& e) {

        ROS_ERROR("cv_bridge exception: %s", e.what());

    imshow("Kinect RGB image", cv_ptr->image);

Does anyone know what might cause this problem? I am using the newest version of Diamondback.


Sebastian Aslund

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What image topic are you subscribed to?
fergs gravatar image fergs  ( 2011-03-05 02:38:20 -0500 )edit

4 Answers

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answered 2011-03-05 02:36:16 -0500

Pi Robot gravatar image

Hi Sebastian,

Here's a similar piece bit of Python code that works for me with my Kinect. Like you, I am using the latest version of Diamondback and the latest Ni stack. The steps I am using are:

$ roslaunch openni_camera openni_node.launch

$ rosrun pi_head_tracking_tutorial

where of course the second line will be different for you. Here is the code. If you run it as a node, you'll also have to change the manifiest name in the roslib.load_manifiest('pi_head_tracking_tutorial') line.

#!/usr/bin/env python

import roslib
import sys
import rospy
import cv
from std_msgs.msg import String
from sensor_msgs.msg import Image
from cv_bridge import CvBridge, CvBridgeError

class vision_node:
    def __init__(self):

        self.cv_window_name = "OpenCV Image"

        cv.NamedWindow(self.cv_window_name, 1)
        self.bridge = CvBridge()
        self.image_sub = rospy.Subscriber("/camera/rgb/image_color", Image,\

    def callback(self, data):
          cv_image = self.bridge.imgmsg_to_cv(data, "bgr8")
        except CvBridgeError, e:
          print e

        cv.ShowImage(self.cv_window_name, cv_image)

def main(args):
      vn = vision_node()
      except KeyboardInterrupt:
        print "Shutting down vison node."

if __name__ == '__main__':
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answered 2011-03-09 20:28:04 -0500

Miguel Prada gravatar image

Hi Sebastian,

I had the same issue and found out that using toCvShare instead of toCvCopy resulted in an image with good colors. Maybe you can use that until this issue is fixed.

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I will try, thanks
Aslund gravatar image Aslund  ( 2011-03-25 07:43:25 -0500 )edit

answered 2011-03-05 08:42:54 -0500

Aslund gravatar image

I managed to make it work and it returns the image nicely, posted a mail on the mailing list pointing out that there is apparently an error in the cv_bridge for diamondback, as using the tutorial for cturtle also returned a nice image.

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I've been using cv_bridge under diamondback without issue -- so I don't think there is a bug in the cv_bridge itself, perhaps you could post the entire source code of the node you have that fails.
fergs gravatar image fergs  ( 2011-03-05 08:58:57 -0500 )edit

answered 2011-03-05 03:15:08 -0500

Aslund gravatar image

I cant see any difference between your code and my own, besides the language used, so I have tried running your code but I get the following error:

  • [rosbuild] Building package ros_kinect_template
  • [rosbuild] Cached build flags older than manifests; calling rospack to get flags
  • [rosbuild] Including /opt/ros/diamondback/stacks/ros_comm/clients/rospy/cmake/rospy.cmake
  • [rosbuild] Including /opt/ros/diamondback/stacks/ros_comm/clients/roslisp/cmake/roslisp.cmake
  • [rosbuild] Including /opt/ros/diamondback/stacks/ros_comm/clients/cpp/roscpp/cmake/roscpp.cmake
  • -- Configuring done CMake Error: CMake can not determine linker language for target:rosCv
  • CMake Error: Cannot determine link language for target "rosCv".

rosCv was a quick node name for your code, I am not used to python in any way, so I do not know if I missed something. I added rospy to my manifest file. I added to my src folder, copied your code, changed the second line to roslib.load_manifest('ros_kinect_temp late') and in my cmake list wrote rosbuild_add_executable(rosCv src/

If someone else have an idea to what might be wrong, then do not hesitate to write :)



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You don't need to build python code -- there is no need for rosbuild_add_executable. Instead, just make the python script executable (using chmod).
fergs gravatar image fergs  ( 2011-03-05 04:58:02 -0500 )edit

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Asked: 2011-03-05 02:18:10 -0500

Seen: 3,200 times

Last updated: Mar 09 '11