remove bounding boxes inside bounding boxes for number recognition - c++

I am trying a number recognition. However after contour finding. I get bounding boxes inside the main bounding box for numbers 0,6,8 ... as shown in figure. Please help me with this initial step of image processing.
I have tried using group rectangles but they are not working. Please check the code below. Thank you.
Image: http://tinypic.com/r/1twx05/5
int main()
{
Mat inimage, gray;
inimage = imread("sample.jpg");
cvtColor(inimage, gray, COLOR_BGR2GRAY);
GaussianBlur(gray, gray, Size(5,5), 0);
adaptiveThreshold(gray, gray, 255, ADAPTIVE_THRESH_GAUSSIAN_C, THRESH_BINARY_INV, 11, 0);
vector<vector<Point> > contours;
vector<Vec4i> hierarchy;
findContours( gray, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );
vector<vector<Point> > contours_poly( contours.size() );
vector<Rect> boundRect( contours.size() );
for( int i = 0; i < contours.size(); i++ )
{
approxPolyDP( Mat(contours[i]), contours_poly[i], 3, true );
boundRect[i] = boundingRect( Mat(contours_poly[i]) );
}
//groupRectangles(boundRect, 1, 0.2);
Scalar color = Scalar(0,0,255);
for( int i = 0; i< contours.size(); i++ )
{
//drawContours( inimage, contours_poly, i, color, 1, 8, vector<Vec4i>(), 0, Point() );
rectangle( inimage, boundRect[i].tl(), boundRect[i].br(), color, 1, 8, 0 );
}
namedWindow( "Contours", CV_WINDOW_AUTOSIZE );
imshow( "Contours", inimage );
waitKey(0);
return 0;
}

try to use the flag: CV_RETR_EXTERNAL instead of CV_RETR_TREE
as stated in the docs it tells to take only outer contours.
Or follow the tree hierarchy to drop nested contours (read the docs for how-to)

Related

OpenCV C++: Convert big block of white pixels to black

I am new to OpenCV, so apologies if I am not able to express my issue properly.
So, I have an image that I converted to B&W. Now I want to convert all big block (block could be of any shapes) of white pixels to black and leave the small white pixels as it is.
To further explain, please look at the picture below:
This pic
This is from another stackoverflow post but basically what I want to do is get rid of that white box and just have text in my picture. In this picture, I can just put a black box on the top since I know where that white box is but how can I do it when I don't know where that white box is?
Thanks in advance
Edit: An example of a picture that I want is here
You can use minArearect function. This function draws fitted rectangles for each contour. You can filter by setting these rectangle edge lengths.
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
using namespace cv;
using namespace std;
int main()
{
Mat src; Mat src_gray;
int thresh = 100;
RNG rng(12345);
/// Load source image and convert it to gray
src = imread( "/ur/src/image_directory/image.png", 1 );
Mat original = src.clone();
/// Convert image to gray and blur it
cvtColor( src, src_gray, CV_BGR2GRAY );
blur( src_gray, src_gray, Size(3,3) );
/// Create Window
char* source_window = "Source";
namedWindow( source_window, CV_WINDOW_AUTOSIZE );
Mat threshold_output;
vector<vector<Point> > contours;
vector<Vec4i> hierarchy;
/// Detect edges using Threshold
threshold( src_gray, threshold_output, thresh, 255, THRESH_BINARY );
/// Find contours
findContours( threshold_output, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );
/// Find the rotated rectangles for each contour
vector<RotatedRect> minRect( contours.size() );
for( int i = 0; i < contours.size(); i++ )
minRect[i] = minAreaRect( Mat(contours[i]) );
int x1,x2,y1,y2;
/// Draw contours + rotated rects
Mat drawing = Mat::zeros( threshold_output.size(), CV_8UC3 );
Mat result_zero = Mat::zeros( threshold_output.size(), CV_8UC3 );
for( int i = 0; i< contours.size(); i++ )
{
Scalar color = Scalar( rng.uniform(0, 255), rng.uniform(0,255), rng.uniform(0,255) );
// contour
drawContours( drawing, contours, i, color, 1, 8, vector<Vec4i>(), 0, Point() );
// rotated rectangle
Point2f rect_points[4]; minRect[i].points( rect_points );
double length_1 = cv::norm(cv::Mat(rect_points[0]),cv::Mat(rect_points[1]));
double length_2 = cv::norm(cv::Mat(rect_points[1]),cv::Mat(rect_points[2]));
//This if scope for your desired rectangle size.You can set your size according to your rectangle(if it changes)
if(length_1>30 && length_1<100 && length_2>30 && length_2<100)
{
int min_x1 = INT_MAX, max_x2 = 0, min_y1 = INT_MAX, max_y2 = 0;
for( int j = 0; j < 4; j++ )
{
if(rect_points[j].x>max_x2 && rect_points[j].y>max_y2)
{
max_x2 = rect_points[j].x;
max_y2 = rect_points[j].y;
}
if(rect_points[j].x<min_x1 && rect_points[j].y<min_y1)
{
min_x1 = rect_points[j].x;
min_y1 = rect_points[j].y;
}
line( result_zero, rect_points[j], rect_points[(j+1)%4], color, 1, 8 );
}
x1 = min_x1;
x2 = max_x2;
y1 = min_y1;
y2 = max_y2;
}
}
circle(result_zero,Point(x1,y1),3,Scalar(0,255,255),2);
circle(result_zero,Point(x2,y2),3,Scalar(0,255,255),2);
// Here in source image we make the rectangle black according to found points
for(int i=y1-2;i<y2+2;i++)
{
for(int j=x1-2;j<x2+2;j++)
{
src.at<cv::Vec3b>(i,j)[0]=0;
src.at<cv::Vec3b>(i,j)[1]=0;
src.at<cv::Vec3b>(i,j)[2]=0;
}
}
/// Show in windows
namedWindow( "Contours", CV_WINDOW_AUTOSIZE );
imshow("First",original);
imshow( source_window, result_zero );
imshow("Last",src);
imshow( "Contours", drawing );
waitKey(0);
return(0);
}
Source image:
Points:
Result:
Find contours.
For each contour: cv::Rect br = cv::boundingRect(contour)
bwImage(br) = cv::Scalar(0, 0, 0)

OpenCV detect darkened rectangle

I am trying to use OpenCV to isolate the translucent darkened rectangular region which has lots of text overlayed. These rectanglular regions can vay in size and location in the window. Is there a way to detect these darkened regions?
Maybe it would be easier to apply some diff operation and compare to the frame before the dark region overlay is shown?
This should give you all bounding boxes based on two images.
#include <cv.h>
#include <highgui.h>
using namespace cv;
Mat im = imread("original.jpg");
Mat im2 = imread("darkened.jpg");
Mat diff_im = im - im2;
Mat diff_im_binary;
threshold(diff_im, diff_im_binary, 30, 255, THRESH_BINARY);
findContours(diff_im_binary, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );
/// Approximate contours to polygons + get bounding rects and circles
vector<vector<Point> > contours_poly( contours.size() );
vector<Rect> boundRect( contours.size() );
vector<Point2f>center( contours.size() );
vector<float>radius( contours.size() );
for( int i = 0; i < contours.size(); i++ )
{
approxPolyDP( Mat(contours[i]), contours_poly[i], 3, true );
boundRect[i] = boundingRect( Mat(contours_poly[i]) );
}

Extracting different size rectangles from image using opencv

Extracting different size rectangles from image using opencv does not work correctly
It doesn't give us patches of all character, just give one patch, but I want patches of all characters
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
using namespace cv;
using namespace std;
Mat src; Mat src_gray;
int thresh = 100;
int max_thresh = 255;
RNG rng(12345);
/// Function header
void thresh_callback(int, void* );
/** #function main */
int main( int argc, char** argv )
{
/// Load source image and convert it to gray
src = imread( "1a.bmp" );
/// Convert image to gray and blur it
cvtColor( src, src_gray, CV_BGR2GRAY );
blur( src_gray, src_gray, Size(3,3) );
/// Create Window
char* source_window = "Source";
namedWindow( source_window, CV_WINDOW_AUTOSIZE );
imshow( source_window, src );
createTrackbar( " Threshold:", "Source", &thresh, max_thresh, thresh_callback );
thresh_callback( 0, 0 );
waitKey(0);
return(0);
}
/** #function thresh_callback */
void thresh_callback(int, void* )
{
Mat threshold_output;
vector<vector<Point> > contours;
vector<Vec4i> hierarchy;
/// Detect edges using Threshold
threshold( src_gray, threshold_output, thresh, 255, THRESH_BINARY );
/// Find contours
findContours( threshold_output, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );
/// Approximate contours to polygons + get bounding rects and circles
vector<vector<Point> > contours_poly( contours.size() );
vector<Rect> boundRect( contours.size() );
vector<Point2f>center( contours.size() );
vector<float>radius( contours.size() );
for( int i = 0; i < contours.size(); i++ )
{ approxPolyDP( Mat(contours[i]), contours_poly[i], 3, true );
boundRect[i] = boundingRect( Mat(contours_poly[i]) );
minEnclosingCircle( (Mat)contours_poly[i], center[i], radius[i] );
}
/// Draw polygonal contour + bonding rects + circles
Mat drawing = Mat::zeros( threshold_output.size(), CV_8UC3 );
for( int i = 0; i< contours.size(); i++ )
{
Scalar color = Scalar( rng.uniform(0, 255), rng.uniform(0,255), rng.uniform(0,255) );
drawContours( drawing, contours_poly, i, color, 1, 8, vector<Vec4i>(), 0, Point() );
rectangle( drawing, boundRect[i].tl(), boundRect[i].br(), color, 2, 8, 0 );
//circle( drawing, center[i], (int)radius[i], color, 2, 8, 0 );
}
/// Show in a window
namedWindow( "Contours", CV_WINDOW_AUTOSIZE );
imshow( "Contours", drawing );
for(int i = 0; i < boundRect.size(); i++)
{
Mat patch = src(boundRect[i]);
//Do whatever you want with the patch (imshow, imwrite,...)
imshow("Patch",patch);
}
}
I think you don't have to extract the rectangles, because you already have them in your vector<Rect> boundRect.
If you want to get patches of the image that contain the rectangles/characters, you just need to cut them out:
stringstream ss;
for(int i = 0; i < boundRect.size(); i++)
{
ss>>"Patch ">>i;
Mat patch = src(boundRect[i]);
//Do whatever you want with the patch (imshow, imwrite,...)
imshow(ss.str(), patch);
ss.str("");
}
#user, you can also try this in opencv documentation
CvMemStorage* storage = cvCreateMemStorage(0);
CvSeq* contours = 0;
cvFindContours( img, storage, &contours, sizeof(CvContour),
CV_RETR_LIST , CV_CHAIN_APPROX_NONE, cvPoint(0,0) );
for( CvSeq* c=contours; c!=NULL; c=c->h_next)
{
CvRect Rects = cvBoundingRect( c );
}
#dennis i also need to extract line. guide me also

Calculating the area of Bounding Box

Hello StackOverflowers
I have created an application that Segments an image on the basis of a predefined color using inRange function. I then draw bounding box around the detected object.
My question here is how do I determine region properties such as: area, size, height and with, center point.
Here i placed a screen dump example.....
How should i approach to retrieve region properties of these bounding boxes or any other bounding boxes that get drown.......?
vector<vector<Point> > contours;
vector<Vec4i> hierarchy;
findContours(mBlur, contours, hierarchy, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );
/// Approximate contours to polygons + get bounding rects and circles
vector<vector<Point> > contours_poly( contours.size() );
vector<Rect> boundRect( contours.size() );
vector<Point2f>center( contours.size() );
vector<float>radius( contours.size() );
for( int i = 0; i < contours.size(); i++ )
{ approxPolyDP( Mat(contours[i]), contours_poly[i], 3, true );
boundRect[i] = boundingRect( Mat(contours_poly[i]) );
}
/// Draw polygonal contour + bonding rects
Mat drawing = Mat::zeros( range_out.size(), CV_8UC3 );
for( int i = 0; i< contours.size(); i++ )
{
Scalar color = Scalar(255,0,255);
drawContours( drawing, contours_poly, i, color, 1, 8, vector<Vec4i>(), 0, Point() );
rectangle( drawing, boundRect[i].tl(), boundRect[i].br(), color, 2, 8, 0 );
}
Regards
You can get the area by using the built in OpenCV function. There are other functions there too to get everything you need.
Just iterate over the 2D coordinates of the segmented shape (the thin pink line in your pictures, you can found this just checking which pixels are not black and looking into its coordinates) and store maximum and minimum X and Y found. Then, width of is maxX - minX and height is maxY - minY
void visualizeSegments(Mat& img, Mat& dst)
{
vector<vector<Point>> contours;
vector<Vec4i> hierarchy;
findContours(img, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE);
dst=Mat::zeros(img.size(), CV_8UC3);
for(int i = 0; i < contours.size(); i++)
{
//Moments mu = moments(contours[i], true );
//Point2f centroid(mu.m10/mu.m00,mu.m01/mu.m00);
//double area = fabs(contourArea(Mat(contours[i])));
//vector<Point> contours_poly;
//approxPolyDP(Mat(contours[i]), contours_poly, 3, true);
//Rect boundRect = boundingRect(Mat(contours_poly));
drawContours(dst, contours, i, Scalar(255,0,0), -1, 8, hierarchy);
}
}
As stated befor there are a set of usefull functions in OpenCV
1. double contourArea(InputArray contour, bool oriented=false ) : to comute the area
2. double arcLength(InputArray curve, bool closed) : to compute the perimeter
3. Moments moments(InputArray array, bool binaryImage=false ) : to compute the center of gravity
4. void HuMoments(const Moments& m, OutputArray hu) : if you want additional properties that is usefull for classification

Contours / Connected components in OpenCV 2.4.4

I'm currently working on an image with a lot of detected contours.
My goal is to narrow down the number of contours to end up with only the one I'm looking for.
For that I conduct a bunch of tests based on area and bounding box.
For now I do after every step a drawContours for the contours that I want to keep followed by a findContours.
My problem is that I would like to do findContours only once and then just erase the contours I don't want, is this possible?
Current way :
Mat src;
Mat BW;
src = imread("img.bmp", 0);
if( src.channels() > 1)
{
cvtColor(src, src, CV_BGR2GRAY);
}
threshold(src, BW, 100, 255, CV_THRESH_OTSU);
imshow( "Tresh", BW );
Mat dst = Mat::zeros(src.rows, src.cols, CV_8UC3);
Mat dstP = Mat::zeros(src.rows, src.cols, CV_8UC3);
Mat dst1 = Mat::zeros(src.rows, src.cols, CV_8UC3);
Mat dst2 = Mat::zeros(src.rows, src.cols, CV_8UC3);
vector<vector<Point> > contours;
vector<Vec4i> hierarchy;
findContours( BW, contours, hierarchy, CV_RETR_CCOMP, CV_CHAIN_APPROX_SIMPLE );
for( int i = 0; i < contours.size(); i++ )
{
Scalar color( rand()&255, rand()&255, rand()&255 );
drawContours( dst, contours, i, color, 2/*CV_FILLED*/, 8, hierarchy );
}
/// Test on area ******************************************************************
for( int i = 0; i < contours.size(); i++ )
{
if ( contourArea(contours[i], false) > 100 && contourArea(contours[i], false) < 200000)
{
Scalar color( rand()&255, rand()&255, rand()&255 );
drawContours( dst1, contours, i, color, CV_FILLED, 8, hierarchy );
}
}
/// Next test **********************************************************************
cvtColor(dst1, dstP, CV_BGR2GRAY);
findContours( dstP, contours, hierarchy, CV_RETR_CCOMP, CV_CHAIN_APPROX_SIMPLE );
etc
Wanted way :
if ( contourArea(contours[i], false) < 100 && contourArea(contours[i], false) > 200000)
{
contours.erase(i); // Doesn't work
}
Does anyone now how to erase those contours?
PS : I don't care about inner contours, I want all of them to go trough my tests.
EDIT, the solution (pointed out by limonana) is : contours.erase(contours.begin()+i);