Why do I get inverted colors in my images?

asked 2017-11-17 05:56:23 -0600

1495 ●35 ●57 ●69

updated 2017-11-17 05:57:18 -0600

I am fetching images from a camera/webcam and publishing it's images using image_transport. When viewed in RViz the images look correct however when recorded with rosbag the compressed image shows inverted colors.

Here is the node to record the images:

#include <ros/ros.h>
#include <image_transport/image_transport.h>
#include <opencv2/highgui/highgui.hpp>
#pragma GCC diagnostic ignored "-Wunused-parameter"
#include <cv_bridge/cv_bridge.h>
#pragma GCC diagnostic pop

int main(int argc,
         char** argv)
{
  ros::init(argc, argv, "image_publisher");
  ros::NodeHandle nh;
  image_transport::ImageTransport it(nh);
  image_transport::Publisher pub = it.advertise("camera", 1);

  cv::VideoCapture cap;
  if (!cap.open(0))
    return 1;

  ros::Rate loop_rate(25);
  while (nh.ok())
  {
    cv::Mat frame;
    cap >> frame;
    if (frame.empty())
      break;

    sensor_msgs::ImagePtr msg = cv_bridge::CvImage(std_msgs::Header(), "bgr8", frame).toImageMsg();
    pub.publish(msg);
    ros::spinOnce();
    loop_rate.sleep();
  }

  return 0;
}

Minimal example package: https://gitlab.com/InstitutMaupertuis...

RViz

rqt_bag

Why are the colors inverted in the compressed image when reading the bag file?

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Comments

Hello there! Are you sure your format to output these images is "bgr8" and not "rgb8"? This is a typical issue because how openCV handles images, inverting order of input channels of colors. I am not but you can try and give us feedback.

CesarHoyosM ( 2017-11-17 06:51:00 -0600 )edit

@CesarHoyosM I think so while not being 100% sure. If I use rgb8 then the colors are inverted in RViz and in the raw image in the bag file, but then the compressed image has the right colors. In short: this inverts the problem

VictorLamoine ( 2017-11-20 01:41:39 -0600 )edit

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#include <ros/ros.h> #include <opencv2/opencv.hpp> #pragma GCC diagnostic ignored "-Wunused-parameter" #include <cv_bridge/cv_bridge.h> #pragma GCC diagnostic pop int main(int argc, char** argv) { ros::init(argc, argv, "image_publisher"); ros::NodeHandle nh; std::string publish_topic("/webcam"); ros::Publisher pub = nh.advertise<sensor_msgs::Image>(publish_topic, 5); ros::Publisher c_pub = nh.advertise<sensor_msgs::CompressedImage>(publish_topic + "/compressed", 5); cv::VideoCapture cap; if (!cap.open(0)) return 1; ros::Rate loop_rate(25); while (nh.ok()) { cv::Mat frame; cap >> frame; if (frame.empty()) continue; sensor_msgs::ImagePtr msg = cv_bridge::CvImage(std_msgs::Header(), "bgr8", frame).toImageMsg(); sensor_msgs::CompressedImagePtr c_msg = cv_bridge::CvImage(std_msgs::Header(), "rgb8", frame).toCompressedImageMsg(); pub.publish(msg); c_pub.publish(c_msg); ros::spinOnce(); loop_rate.sleep(); } return 0; }

Comments

I will not mark this answer as correct as this is only a "good alternative", it does not answer the question.

VictorLamoine ( 2017-11-27 03:33:53 -0600 )edit

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Why do I get inverted colors in my images?

RViz

rqt_bag

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Why do I get inverted colors in my images?