Using cv::Mat image(opencv) how can i detect object?

Question

Using

Mat image;

I used

inRange(image,Scalar(170,100,0),Scalar(255,255,70),image);

and i detect object in blue, but I can't draw rectangle around the object.

Should I use mask? or something?

inRange(image,Scalar(170,100,0),Scalar(255,255,70),image);
GaussianBlur(image,image,Size(9,9),1.5);

for(int i = 2; i <image.cols-2;i++)
 for(int j = 2; j <image.rows-2;j++){
  if( image.at<Vec3b>(i-1,j-1)[0] > 200 &&
    image.at<Vec3b>(i-1,j)[0] > 200 &&
    image.at<Vec3b>(i-1,j+1)[0] > 200 &&
    image.at<Vec3b>(i,j-1)[0] > 200 &&
    image.at<Vec3b>(i,j)[0] > 200 &&
    image.at<Vec3b>(i,j+1)[0] > 200 &&
    image.at<Vec3b>(i+1,j-1)[0] > 200 &&
    image.at<Vec3b>(i+1,j)[0] > 200 &&
    image.at<Vec3b>(i+1,j+1)[0] > 200 
)
{

    if(min_x > i)
        min_x = i;
    if(min_y >j)
        min_y = j;
    if(max_x < i)
        max_x =i;
    if(max_y < j)
        max_y = j;

}
 }
 if(!(max_x==0 && max_y==0 && min_x==image.rows && min_y == image.cols))
 {
    rectangle(image,Point(min_x,min_y),Point(max_x,max_y),CV_RGB(255,0,0),2);
 }

  imshow("working", image);
  if(waitKey(100) >= 0) break;
}

}

This isn't working and a run time error. I don't know why.. help me!

Answer 1

Some tips:

• Your image might be CV_8U3C, but inRange probably converts it to CV_8U, so better use for output a new Mat instance.

• Use cv::findContours to detect your area.

• Study meanshift used for tracking by opencv which might help you.

Answer 2

You cannot use RGB image for the inrange method. You should transform your image to HSV color space, and use hue range of blue then, which is 95-135. There are so many "blue" possibilities at RGB space.

inRange(image,Scalar(95,0,0),Scalar(135,255,255),image);

The result will be a binary image, just find the contour and draw bounding rectangle around it.