====== Detecting Blue Color ======

===== Introduction =====

This tutorial you will learn to write an other simple program for filtering blue colored objects.In tutorial "How to make ROS and Opencv work together" you would have created a package called "roscv" if you have not done that please follow that tutorial. Another prerequisite for this tutorial is the ardrone. I have given directions  in the first tutorial on how to connect your computer to the ardrone.

===== Add an other source file =====

Step 1:Go to  folder named "src" in the package "roscv"and create a file called "bluetrack.cpp"
 
Step 2: In the empty file and paste the following code and after that save the file.

<code c++ bluetrack.cpp>
#include <ros/ros.h>
#include <stdio.h>
#include <iostream>
#include "std_msgs/String.h"
#include <image_transport/image_transport.h>
#include <cv_bridge/cv_bridge.h>
#include <sensor_msgs/image_encodings.h>
#include <opencv2/imgproc/imgproc.hpp>     //make sure to include the relevant headerfiles
#include <opencv2/highgui/highgui.hpp>
#include <opencv/cv.h>
#include <opencv/highgui.h>
#include <cv_bridge/CvBridge.h>
#include <cvaux.h>
#include<math.h>
#include <cxcore.h>
#include "turtlesim/Velocity.h"
#include <turtlesim/Pose.h>
#include <highgui.h>

/*here is a simple program which demonstrates the use of ros and opencv to do image manipulations on video streams given out as image topics from the monocular vision
of robots,here the device used is a ardrone(quad-rotor).*/
using namespace std;
using namespace cv;
namespace enc = sensor_msgs::image_encodings;
static double r=0,g=0,b=0;
static const char WINDOW[] = "Image window";

class ImageConverter
{
  ros::NodeHandle nh_;
  ros::NodeHandle n;
 ros::Publisher pub ;

  image_transport::ImageTransport it_;    
  image_transport::Subscriber image_sub_; //image subscriber 
  image_transport::Publisher image_pub_; //image publisher(we subscribe to ardrone image_raw)
  std_msgs::String msg;
public:
 ImageConverter()
    : it_(nh_)
  {
      
      pub= n.advertise<turtlesim::Pose>("/drone/walldis", 500);
      image_sub_ = it_.subscribe("/ardrone/image_raw", 1, &ImageConverter::imageCb, this);
     image_pub_= it_.advertise("/arcv/Image",1);
      
     }

  ~ImageConverter()
  {
    cv::destroyWindow(WINDOW);
  }

  void imageCb(const sensor_msgs::ImageConstPtr& msg)
  {
    
     sensor_msgs::CvBridge bridge;//we need this object bridge for facilitating conversion from ros-img to opencv
     IplImage* img = bridge.imgMsgToCv(msg,"bgr8");  //image being converrosbuild_add_executableted from ros to opencv using cvbridge
  
IplImage* img1 = cvCreateImage( cvGetSize(img), IPL_DEPTH_8U, 3 ); 
IplImage* imgThreshedred = cvCreateImage(cvGetSize(img), IPL_DEPTH_8U, 1);
IplImage* imgThreshedgreen = cvCreateImage(cvGetSize(img), IPL_DEPTH_8U, 1);
IplImage* imgThreshedblue = cvCreateImage(cvGetSize(img), IPL_DEPTH_8U, 1);
IplImage* imgThreshedminus = cvCreateImage(cvGetSize(img), IPL_DEPTH_8U, 1);
cvSplit(img, imgThreshedblue, imgThreshedgreen, imgThreshedred, NULL);
cvSub(imgThreshedblue,imgThreshedgreen,imgThreshedminus,0);
cvSub(imgThreshedminus,imgThreshedred,imgThreshedminus,0);


cvInRangeS(imgThreshedred, cvScalar(254), cvScalar(255), imgThreshedINrange); 
cvShowImage( "imgTHRESHOLDminus",imgThreshedminus);
cvShowImage( "IMG",img);


  cvWaitKey(2);   


  
}
};


int main(int argc, char** argv)
{
  ros::init(argc, argv, "image_converter");
  ImageConverter ic;
  ros::spin();
 	
  return 0;
}
</code>

===== Make changes in the CMakeLists.txt =====

Step 1:
Open up the file named "CMakeLists.txt" and search for the lines beginning with "rosbuild_add_executable". In that add the file you created which is  "bluetrack.cpp". Save and close the file.

===== Test the code =====

Step 1:
While you are at the folder of the package  "roscv". Open up a terminal and enter

  cmake . 

After that enter

  rosmake

Make sure rosmake gets you "0" failures.

Step 2:
Turn on the ARDRONE and connect to it using WiFi.Now enter the following commands one after the other :

  roscore  
  rosrun ardrone_brown ardrone_driver 
  rosrun roscv roscv 

You should be getting two windows.  I used a blue cup for detecting and the here is a picture of that.

{{dylanw:beforefilter.png}}\\ 

{{dylanw:Bluecupfilter.png}}\\