Hello All, I want to compare two(or more) consecutive image to detect movement within a range. For example, if there is anything in front of kinect camera within 60cm then it will detect and then just tell me if the object is moving or stationary. I repeat, I do not need to track any object, do not need to detect any pattern. Just need ato know if anything is moving infront of the camera within a range. I am using ros indigo, ubuntu 14.04 and having kinect cam. I am subscribing the topic /camera/depth/imageraw and getting image of type sensormsgs::Image. So now I want to compare the two image. If there is a difference in the images then the decision is that there is something moving in front of the camera. I want to use opencv image comparison feature.

edit 1: I used another node which subscribed /camera/depth/points , and from there i detected if there is something in front of camera within 60cm range. Then i published a boolean flag. Using this node below I was trying to know if there is something within the range, it will tell us if the object is static or moving. But now I want to do it in the same node below as I came to know /camera/depth/imageraw gives image with depth data and I can get it using opencv function int depth = imagecur.at(cv::Point(j,i));

but somehow I am not getting it exactly. Like if there is nothing moving in front of camera, i get the response something is moving. Because in each frame there is difference of values. My question is, if nothing is moving infront of camera, then why the data array are not identical for sequential images ?

I am going to update the codes below,

include

include

include "std_msgs/String.h"

include "geometry_msgs/Twist.h"

include

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//Store all constants for image encodings in the enc namespace to be used later. namespace enc = sensormsgs::imageencodings;

using namespace::std; using namespace cv;

sensormsgs::Image imgprevious, imgcurrent, imgprimary; stdmsgs::Bool checkmovingobj , obstaclefound, ismovingobs; bool checkmovingobs= true;

ros::Publisher pub, dec_pub;

double scalelinear, scaleangular; void deccallback(const stdmsgs::Bool::ConstPtr& msg) { checkmovingobs = msg->data; } void callback(const sensor_msgs::Image::ConstPtr& msg){

 if(check_moving_obs)
 {
     if(img_previous.data.size() == 0)
     {
         img_previous = *msg;
         img_primary = *msg;
     }
     else
         {img_previous = img_current;}
    img_current = *msg;

    cout<<"------------------------current image info :---------:"<<img_current.data.size()<<"\n";
    cout<<"------------------------Height :---------:"<<img_current.height<<"\n";
    cout<<"------------------------Width :---------:" <<img_current.width<<"\n";

    cout<<"------------------------previous image info :---------:"<<img_previous.data.size()<<"\n";
    cout<<"------------------------Height :---------:"<<img_previous.height<<"\n";
    cout<<"------------------------Width :---------:" <<img_previous.width<<"\n";


        //Convert from the ROS image message to a CvImage suitable for working with OpenCV for processing
            cv_bridge::CvImagePtr cv_ptr_prev, cv_ptr_cur;
            cv::Mat image_cur, image_pre, differenceImage;
            //thresholded difference image (for use in findContours() function)
            cv::Mat thresholdImage;

            try
            {

                //Always copy, returning a mutable CvImage
                //OpenCV expects color images to use BGR channel order.
                cv_ptr_cur = cv_bridge::toCvCopy(msg, enc::TYPE_16UC1);//cv_bridge::toCvCopy(img_current, enc::BGR8);
                cv_ptr_prev = cv_bridge::toCvCopy(img_previous, enc::TYPE_16UC1);


                image_cur = cv_ptr_cur->image;
                image_pre = cv_ptr_prev->image;
                int count_diff=0;
                bool motion_detected = false;

                //perform frame differencing with the sequential images.
                cv::absdiff(image_cur,image_pre,differenceImage);
                cout<<"~~~~~~~~~~~~~~~~~~~~~~difference image info :---------:"<<differenceImage.total()<<"\n";
                for(int j=0; j<image_cur.rows; ++j)
                {
                    if(count_diff > 150) //this is just a random try to give a threshhold value. 
                    {
                        break;
                    }
                        for(int i=0; i<image_cur.cols; ++i)
                        {
                            int depth = image_cur.at<short int>(cv::Point(j,i));
                            if(depth < 0.6)
                            {
                                if(image_cur.at<cv::Vec3b>(j,i) != image_pre.at<cv::Vec3b>(j,i))
                                {
                                    cout<<"i : "<<i<<" ... j : "<<j<<"\n";
                                    cout<<"iamge curr : "<< image_cur.at<cv::Vec3b>(j,i)<<"\n";
                                    cout<<"iamge prev : "<< image_pre.at<cv::Vec3b>(j,i)<<"\n";
                                    count_diff++;
                                }

                                if(count_diff > 150)
                                {
                                    motion_detected = true;
                                    break;
                                }
                            }
                        }
                }
                if(motion_detected)
                {
                    cout<<"------------------------something is moving stop and wait---------"<<"\n";
                }

                //threshold intensity image at a given sensitivity value
                //cv::threshold(differenceImage,thresholdImage, 20,255,cv::THRESH_BINARY);
                //show the difference image and threshold image
                //cv::imshow("Difference Image",differenceImage);
                //cv::imshow("Threshold Image", thresholdImage);

                //imshow("Frame1",image_pre);

            }
            catch (cv_bridge::Exception& e)
            {
                //if there is an error during conversion, display it
                ROS_ERROR("cv_bridge exception: %s", e.what());
                return;
            }
       //pub.publish( msg_decission);
    }
 sleep(1);//use sleep if you want to delay loop.

}

int main(int argc, char** argv) { ros::init(argc, argv,"listenerdepthcomparer"); ros::NodeHandle nh; nh.param("scalelinear", scalelinear, 1.0); nh.param("scaleangular", scaleangular, 1.0); ros::Subscriber sub = nh.subscribe("/camera/depth/imageraw", 1, callback); //ros::Subscriber sub = nh.subscribe<sensormsgs::Image>("/camera/depthregistered/imageraw", 1, callback);

ros::Subscriber decsub = nh.subscribe<stdmsgs::Bool>("obstacleDetectionDecision", 1, dec_callback);

decpub = nh.advertise<geometrymsgs::Twist>("/cmdvel", 1, true); //ros::Subscriber sub = nh.subscribe<sensormsgs::PointCloud2>("/camera/depth/points", 1, chatterCallback); //kinect ros::spin(); }

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Can anyone please help me what is wrong here....?