inRange Query image output - opencv

Question

I've started learning opencv and have written the code below to obtain the output of an image (from input camera) in hsv and an inRange image !
the hsv output is fine but inRange o/p is just blank :| plz help am stumped
int main(int argc[], char** argv[])
{
VideoCapture camera(CV_CAP_ANY);
Mat input;
Mat output(Size(input.size().height,input.size().width),input.type());
Mat img_thresh(Size(640,480),input.type());
namedWindow("input",0);
namedWindow("output",0);
namedWindow("threshold",0);
cv::Scalar hsv_min = cvScalar(0, 30, 80, 0);
cv::Scalar hsv_max = cvScalar(20, 150, 255, 0);
for(;;)
{
camera >> input;
cvtColor(input,output,CV_BGR2HSV,1);
cv::inRange(input,hsv_min,hsv_max,img_thresh);
imshow("input",input);
imshow("output",output);
imshow("threshold",img_thresh);
cv::waitKey(40);
}
return 0;
}

Answer 1

You apply the inRange function to the input BGR image. You have to apply it to the HSV image, named output in your code. So the line should be :
cv::inRange(output,hsv_min,hsv_max,img_thresh);
Your code was working but you did not use the right image !
If you want to know HSV value in your image I suggest you to use :
cvSetMouseCallback("input", getObjectColor);
And :
void getObjectColor(int event, int x, int y, int flags, void *param = NULL) {
// Vars
CvScalar pixel;
IplImage *hsv;
if(event == CV_EVENT_LBUTTONUP) {
// Get the hsv image
hsv = cvCloneImage(image);
cvCvtColor(image, hsv, CV_BGR2HSV);
// Get the selected pixel
pixel = cvGet2D(hsv, y, x);
cvShowImage("getObjColor", hsv);
// Change the value of the tracked color with the color of the selected pixel
h = (int)pixel.val[0];
s = (int)pixel.val[1];
v = (int)pixel.val[2];
cout << "Color HSV = h:" << pixel.val[0] << " | s:" << pixel.val[1] << " | v:" << pixel.val[2] << endl;
// Release the memory of the hsv image
cvReleaseImage(&hsv);
}
}
You will need to create some variables to make this work, the code was taken from the internet (can't remember where !)