Ignore connected component inside another one - c++

Question

I'm trying to separate the background (green field and light green towel) from the objects using OpenCV so I segmented the following image manually:
By bordering the objects in red and coloring blue the connected components which should not be taken into consideration as you can see in the bottom right of the image:
After threasholding on 254 the channels R and B, I got the following:
Channel Red
Channel Blue
If I fulfill the all contours of red channel using
findContours( bordersRed, contoursRedChannel, hierarchyRedChannel, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, cv::Point(0, 0) );
for (int index = 0; index < contoursRedChannel.size(); index ++)
{
drawContours( bordersRed, contoursRedChannel, index, colorForMask, CV_FILLED, 8, hierarchyRedChannel, 0, cv::Point() );
}
the bottom right corner will be like:
But what I need is to ignore the contours that contains only blue points in order to have something like:
so I have to combine the red with blue channels to get it but don't know how yet. Any advice would be appreciated.
Thanks.

Answer 1

You can do that using floodFill, assuming you know a point inside the shape you want to fill.
Result starting from your "Channel red":
Code:
#include <opencv2/opencv.hpp>
#include <iostream>
using namespace std;
using namespace cv;
int main()
{
// Your image
Mat1b img = imread("path_to_image", IMREAD_GRAYSCALE);
// Assume you know a point inside the shape
Point seed(930, 370);
// Apply floodfill
floodFill(img, seed, Scalar(255));
// Show image
imshow("Result", img);
waitKey();
return 0;
}
UPDATE
Once you fill the contours in both masks with drawContours(... CV_FILLED), you can simply XOR the two mask:
Code:
#include <opencv2\opencv.hpp>
#include <vector>
#include <algorithm>
using namespace std;
using namespace cv;
int main()
{
// Load the two mask
Mat1b channel_red_mask = imread("channel_red.png", IMREAD_GRAYSCALE);
Mat1b channel_blue_mask = imread("channel_blue.png", IMREAD_GRAYSCALE);
// Use just the bottom right part
Rect roi(Point(800, 270), Point(channel_red_mask.cols, channel_red_mask.rows));
channel_red_mask = channel_red_mask(roi).clone();
channel_blue_mask = channel_blue_mask(roi).clone();
// Fill all contours, in both masks
{
vector<vector<Point>> contours;
findContours(channel_red_mask.clone(), contours, RETR_LIST, CHAIN_APPROX_SIMPLE);
for (int i = 0; i < contours.size(); ++i)
{
drawContours(channel_red_mask, contours, i, Scalar(255), CV_FILLED);
}
}
{
vector<vector<Point>> contours;
findContours(channel_blue_mask.clone(), contours, RETR_LIST, CHAIN_APPROX_SIMPLE);
for (int i = 0; i < contours.size(); ++i)
{
drawContours(channel_blue_mask, contours, i, Scalar(255), CV_FILLED);
}
}
// XOR the masks
Mat1b xored = channel_red_mask ^ channel_blue_mask;
imshow("XOR", xored);
waitKey();
return 0;
}