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How to save subscribed image in any location

asked 2014-11-13 04:31:58 -0500

KDROS gravatar image

Hello Everyone, I am using OpenCV 2.9 and ROS Hydro. i used this Publisher for publish image and used Subscriber for subscribing images. I am able to show that image but how to save it in computer?? I Used imwrite like this after imshow()

cv::imwrite("//home//keshav//image.jpg",cv_bridge::toCvShare(msg, "bgr8")->image);


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Add what happend? Error or something?

Wolf gravatar image Wolf  ( 2014-11-13 07:25:12 -0500 )edit

there is no error but also It is not saving any images. I seached in net somewhere i found that I should use latest opencv for that..but i dont want to install that one.

KDROS gravatar image KDROS  ( 2014-11-13 23:35:03 -0500 )edit

Does the folder "//home//keshav//" exist? Usually it should be "/home/keshav/image.jpg" but that should not matter... Does imwrite return true? It should return true on success...

Wolf gravatar image Wolf  ( 2014-11-14 01:06:23 -0500 )edit

hoe to check that one..

KDROS gravatar image KDROS  ( 2014-11-16 23:34:17 -0500 )edit

if ( cv::imwrite("//home//keshav//image.jpg",cv_bridge::toCvShare(msg, "bgr8")->image) ) { ROS_INFO( "Returned true" ); } else { ROS_INFO( "Returned false" ); }

Wolf gravatar image Wolf  ( 2014-11-17 05:49:03 -0500 )edit

try { cv::imshow("view", cv_bridge::toCvShare(msg,"bgr8")->image); cv_ptr = cv_bridge::toCvCopy(msg, enc::BGR8);
if ( cv::imwrite("//home//keshav//image.jpg",cv_bridge::toCvShare(msg, "bgr8")->image) ) { ROS_INFO( "Returned true2" ); } else { ROS_INFO( "Returned false2" ); } }

KDROS gravatar image KDROS  ( 2014-11-17 06:30:01 -0500 )edit

It is neither returning true nor false.. :-(

KDROS gravatar image KDROS  ( 2014-11-17 06:30:27 -0500 )edit

I have to create ROS nodes, one node can capture images using webcam & 2nd node can publish and third node can subscribe. first am unable to capture also, I can publish and subscribe but imwrite is not working. Mr. Wolf plz share some solid links or code that I can easily execute for this purpose

KDROS gravatar image KDROS  ( 2014-11-17 06:33:31 -0500 )edit

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answered 2014-11-18 15:46:26 -0500

Wolf gravatar image

updated 2014-11-18 15:47:06 -0500

If you just want to save an image, just have a look at the cv_bridge tutorial

And add a cv::imwrite after the image was converted to cv::Mat:

#include <ros/ros.h>
#include <image_transport/image_transport.h>
#include <cv_bridge/cv_bridge.h>
#include <sensor_msgs/image_encodings.h>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <sstream>                                                 // Added this

static const std::string OPENCV_WINDOW = "Image window";

class ImageConverter
  ros::NodeHandle nh_;
  image_transport::ImageTransport it_;
  image_transport::Subscriber image_sub_;
  image_transport::Publisher image_pub_;

    : it_(nh_)
    // Subscrive to input video feed and publish output video feed
    image_sub_ = it_.subscribe("/camera/image_raw", 1, 
      &ImageConverter::imageCb, this);
    image_pub_ = it_.advertise("/image_converter/output_video", 1);



  void imageCb(const sensor_msgs::ImageConstPtr& msg)
    cv_bridge::CvImagePtr cv_ptr;
      cv_ptr = cv_bridge::toCvCopy(msg, sensor_msgs::image_encodings::BGR8);
    catch (cv_bridge::Exception& e)
      ROS_ERROR("cv_bridge exception: %s", e.what());

    // Draw an example circle on the video stream
    if (cv_ptr->image.rows > 60 && cv_ptr->image.cols > 60)
      cv::circle(cv_ptr->image, cv::Point(50, 50), 10, CV_RGB(255,0,0));

    // Update GUI Window
    cv::imshow(OPENCV_WINDOW, cv_ptr->image);

    static int image_count = 0;                                // added this
    std::stringstream sstream;                               // added this
    sstream << "my_image" << image_count << ".png" ;                  // added this
    ROS_ASSERT( cv::imwrite( sstream.str(),  cv_ptr->image ) );      // added this
    image_count++;                                      // added this

    // Output modified video stream

int main(int argc, char** argv)
  ros::init(argc, argv, "image_converter");
  ImageConverter ic;
  return 0;

This should save you the images with ascending counter locally in the folder where you start the node via rosrun .....

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Thanq Wolf Sir..I think It would work, I will try it. One more question if you help. I was Using usb_cam driver for capturing image from usb camera. It auto publish (as I understand) when we press right click for saving images? How should I write subscriber for that.

KDROS gravatar image KDROS  ( 2014-11-18 22:42:42 -0500 )edit

If I use above code by changing TOPIC name. will it work?

KDROS gravatar image KDROS  ( 2014-11-18 23:10:12 -0500 )edit

jep, that should work...

Wolf gravatar image Wolf  ( 2014-11-19 04:39:45 -0500 )edit

Sorry, Its not working. I saw the usb_cam files, It is publishing image and camera info, what changes are required in above code.

KDROS gravatar image KDROS  ( 2014-11-19 23:02:17 -0500 )edit

What is not working? you need to renap the topic of the usb_cam to /camera/image_raw . Is something published to /image_converter/output_video?

Wolf gravatar image Wolf  ( 2014-11-20 01:40:45 -0500 )edit

One silly doubt I have.. When usb_cam will publish the image? As soon as I will save(by right clicking) or after some time frequently

KDROS gravatar image KDROS  ( 2014-11-20 04:22:19 -0500 )edit

waiting for reply

KDROS gravatar image KDROS  ( 2014-11-23 23:33:04 -0500 )edit

I am not familiar with the usb_cam driver. Typically cam drivers publish at constant frequency. You can check messages are comming using comand "rostopic echo --noarr /your_image_topic" (--noarr skips array data so you can actually see something)

Wolf gravatar image Wolf  ( 2014-11-24 01:51:00 -0500 )edit

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Asked: 2014-11-13 04:31:58 -0500

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Last updated: Nov 18 '14