ROS Resources: Documentation | Support | Discussion Forum | Index | Service Status | Q&A
Ask Your Question

Problem with converting image from depth to grayscale

asked 2013-11-03 15:36:02 -0500

prasanna.kumar gravatar image

updated 2016-10-24 08:37:03 -0500

ngrennan gravatar image

I am trying to convert depth image from (/camera/depth/image) to grayscale image (/camera/rgb/image_mono). This is my code.

#include "ros/ros.h"
#include "sensor_msgs/Image.h"
#include <std_msgs/UInt8.h>

using namespace std;
using namespace ros;

class ImageConverter
        NodeHandle gdd;
        Subscriber depth_sub;
        Publisher gray_pub;

        void imageCb(const sensor_msgs::Image::ConstPtr& );


                depth_sub = gdd.subscribe("/camera/depth/image", 1, &ImageConverter::imageCb, this);
                gray_pub = gdd.advertise<sensor_msgs::Image>("depthTOgreyscale_image", 1);                


void ImageConverter::imageCb(const sensor_msgs::ImageConstPtr& depth_image)

        sensor_msgs::Image gray_image;       
        gray_image.header.seq = depth_image->header.seq;
        gray_image.header.stamp = depth_image->header.stamp;
        gray_image.header.frame_id = "/camera_rgb_optical_frame";
        gray_image.height = 480;
        gray_image.width = 640;
        gray_image.encoding = "mono8";
        gray_image.is_bigendian = 0;
        gray_image.step = 640;

        float max_depth = 0;
        for(int i=0; i<depth_image->height; i++)
                for(int j=0; j<depth_image->width; j++)

                        float distance = depth_image->data[i*depth_image->width+j];
                        if (distance == distance) { 
                            max_depth = max(distance, max_depth);


        ROS_INFO("%f", max_depth);
       //ACTUAL CONVERSION             
       for(int i=0; i<depth_image->height; i++)
                for(int j=0; j<depth_image->width; j++)
             [i*depth_image->width+j] = (unsigned int)(depth_image->data[i*depth_image->width+j]/max_depth*255);    




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

I am able to read the depth data and convert it to UInt8C1 format but for some reason I am getting seg fault when I try to write data on my grayscale topic.

Is there a mistake I am doing I am not seeing or is there some way around it ?

edit retag flag offensive close merge delete

1 Answer

Sort by ยป oldest newest most voted

answered 2013-11-04 02:13:22 -0500

Ben_S gravatar image

Try initializing with an properly sized array. Also you should check if the size of the incoming image and the output match. (Or set width, height and step accordingly to the input)

edit flag offensive delete link more

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Question Tools

1 follower


Asked: 2013-11-03 15:36:02 -0500

Seen: 2,154 times

Last updated: Feb 25 '14