Finding only big blobs on image - c++

Question

Hello I'm trying to find characters on this image.
This is my image after some preprocessing I recieved this image.
Now I'm trying to do connected component labeling to find blobs. however I get a lot of small blobs too.
#include <iostream>
#include <vector>
#include <stdio.h>
#include <stdlib.h>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
using namespace cv;
using namespace std;
void FindBlobs(const Mat &binary, vector < vector<Point2i> > &blobs);
int main(int argc, char **argv)
{
Mat img = imread("adaptive.png", 0);
if(!img.data) {
cout << "File not found" << endl;
return -1;
}
namedWindow("binary");
namedWindow("labelled");
Mat output = Mat::zeros(img.size(), CV_8UC3);
Mat binary;
vector < vector<Point2i > > blobs;
threshold(img, binary, 0, 1, THRESH_BINARY_INV);
FindBlobs(binary, blobs);
// Randomy color the blobs
for(size_t i=0; i < blobs.size(); i++) {
unsigned char r = 255 * (rand()/(1.0 + RAND_MAX));
unsigned char g = 255 * (rand()/(1.0 + RAND_MAX));
unsigned char b = 255 * (rand()/(1.0 + RAND_MAX));
for(size_t j=0; j < blobs[i].size(); j++) {
int x = blobs[i][j].x;
int y = blobs[i][j].y;
output.at<Vec3b>(y,x)[0] = b;//Vec3b RGB color order
output.at<Vec3b>(y,x)[1] = g;
output.at<Vec3b>(y,x)[2] = r;
}
}
imshow("binary", img);
imshow("labelled", output);
waitKey(0);
return 0;
}
void FindBlobs(const Mat &binary, vector < vector<Point2i> > &blobs)
{
blobs.clear();
Mat label_image;
binary.convertTo(label_image, CV_32SC1);
int label_count = 2; // starts at 2 because 0,1 are used already
for(int y=0; y < label_image.rows; y++) {
int *row = (int*)label_image.ptr(y);
for(int x=0; x < label_image.cols; x++) {
if(row[x] != 1) {
continue;
}
Rect rect;
floodFill(label_image, Point(x,y), label_count, &rect, 0, 0, 4);
vector <Point2i> blob;
for(int i=rect.y; i < (rect.y+rect.height); i++) {
int *row2 = (int*)label_image.ptr(i);
for(int j=rect.x; j < (rect.x+rect.width); j++) {
if(row2[j] != label_count) {
continue;
}
blob.push_back(Point2i(j,i));
}
}
blobs.push_back(blob);
label_count++;
}
}
}
so with this algorithm I recieve blobs
but when I do
if(blobs.size()>50) {
blob.push_back(Point2i(j,i));
}
I recieve black screen. however when I try to
if(blob.size()<50){
blob.push_back(Point2i(j,i));
}
I recieve small blobs what can be the actual problem here ?

Answer 1

Guess you want to store those "big" blobs?
If so, change the following code
blobs.push_back(blob);
label_count++;
to this:
if(blob.size() > 50){
blobs.push_back(blob);
}
label_count++;
And you can receive picture like this: