JavaCV findContours outlining the image instead of finding the contour - opencv

Question

I am trying to find that whether there is any rectangle/square present inside my area of interest. Here is what I have achieved till now.
Below is the region of interest which I snipped out of the original image using JavaCV.
Mat areaOfInterest = OpenCVUtils.getRegionOfInterest("image.jpg",295,200,23,25);
public static Mat getRegionOfInterest(String filePath , int x, int y, int width, int height){
Mat roi = null;
try{
Mat image = Imgcodecs.imread(filePath);
Rect region_of_interest= new Rect(x,y,width,height);
roi = image.submat(region_of_interest);
}catch (Exception ex){
}
return roi;
}
Now I'm trying to find whether there is any rectangle present in the area of interest. I have used following lines of code to detect that as well.
Mat gray = new Mat();
Mat binary = new Mat();
Mat hierarchy = new Mat();
ArrayList<MatOfPoint> contours = new ArrayList<>();
cvtColor(image,gray,COLOR_BGR2GRAY);
Core.bitwise_not(gray,binary);
findContours(binary,contours,hierarchy,RETR_EXTERNAL,CHAIN_APPROX_NONE);
if(contours.size() > 0){
for (MatOfPoint contour:contours) {
Rect rect = boundingRect(contour);
/// x = 0, y = 1 , w = 2, h =3
Point p1 = new Point(rect.x,rect.y);
Point p2 = new Point(rect.width + rect.x, rect.height+rect.y);
rectangle(image,p1,p2,new Scalar(0,0,255));
Imgcodecs.imwrite("F:\\rect.png",image);
}
}
But instead of finding the the square inside the image it is outlining the parts of the image as following.
It would be great if someone pushes me in the right direction.

Answer 1

OpenCV's findContours() treats the input image as binary, where everything that is 0 is black, and any pixel >0 is white. Since you're reading a jpg image, the compression makes it so that most white pixels aren't exactly white, and most black pixels aren't exactly black. Thus, if you have an input image like:
3 4 252 250 3 1
3 3 247 250 3 2
3 2 250 250 2 2
4 4 252 250 3 1
3 3 247 250 3 2
3 2 250 250 2 2
then findContours() will just outline the whole thing, since to it it's equivalent to all being 255 (they're all > 0).
All you need to do is binarize the image with something like threshold() or inRange(), so that your image actually comes out to
0 0 255 255 0 0
0 0 255 255 0 0
0 0 255 255 0 0
0 0 255 255 0 0
0 0 255 255 0 0
0 0 255 255 0 0
Then you'd correctly get the outline of the 255 block in the center.