HSV segmentation based on mouse click

Question

I am trying to do some basic image segmentation. The thereshold values for the HSV are to be determined from the pixel value where the mouse is clicked. I cannot get it to work. Here is what I wrote so far:

#include <iostream>
#include "opencv2/opencv.hpp"
#include <cv.h>
#include "opencv/highgui.h"

using namespace std;
using namespace cv;

Mat edges,frame,bw,hsv,dst,src_gray,probabilistic_hough, HSV_image;
int H=110,S=40,V=140;
int border=80;
int linethreshold=180,linelengthslider=30,linegapslider=3, HT_threshold=10;
int min_threshold = 50;

void printHSVValues(int event, int x, int y, int, void* );
void changeborder( int, void* );

Scalar hsvlow(0,0,0),hsvhigh(180,255,255);

int c=0;

void printHSVValues(int event, int x, int y, int, void* );

int main ( int argc, char **argv )
{
    VideoCapture cap(1);

    namedWindow("edges",1);
    namedWindow("segmented",1);

    setMouseCallback( "edges", printHSVValues, 0 );

    while (c != 'q') {
        cap >> frame;
        imshow("edges",frame);
        c= (char)waitKey(100);
    }

    return 0;
}

void  printHSVValues(int event, int x, int y, int, void* ){

    int loop;
    float change;

    if( event == EVENT_LBUTTONDOWN ) {
        cvtColor(frame, HSV_image, CV_BGR2HSV);
        Vec3b p = HSV_image.at<float>(y,x);
        for (loop=0;loop<3;loop++) { 
            change=p[loop]*0.01; 
            hsvlow[loop]  = p[loop] - change; 
            hsvhigh[loop] = p[loop] + change;
        }
        inRange( HSV_image, hsvlow,hsvhigh,bw);
        imshow("segmented",bw);
    }
}

Where am I messing up? Thanks in advance.

DY.

Answer 1

You are not accessing Mat-values correctly. The image has 3-channels as you correctly assigned the variable the type Vec3b, yet you retrieve a floatvalue from the image. The correct way would be:

Vec3b p = HSV_image.at<Vec3b>(y,x);