Hi guys
I have the following image
I want to extract the following part circled red in the image as shown
The problem is both the background and the box to extract are white..
How can i perform thresholding such that i get only the box as output.
I am using python 2.7 with cv2
I would do a simple threshold on the image. Then use cv::findContours() an choose the correct contours with cv::contourArea(). After that you can cut out the region with creating a rectangle around it (cv::boundingRect) and copy the specific part to a new cv::Mat.
Perhabs you have to dilate the image before, if the small bright regions are not seperated from the large ones by cv::findContours(). Also you can make the size of the bounding rectangle a bit larger if you want.
sample c++ code below can easily be converted to Python
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
using namespace cv;
using namespace std;
int main( int, char** argv )
{
/// Load source image
Mat src = imread(argv[1]);
if (src.empty())
{
cerr << "No image supplied ..." << endl;
return -1;
}
/// Convert image to gray
Mat src_gray;
cvtColor( src, src_gray, COLOR_BGR2GRAY );
threshold( src_gray, src_gray, 250, 255, THRESH_BINARY );
//erode( src_gray, src_gray, Mat());
/// Find contours
vector<vector<Point> > contours;
findContours( src_gray, contours, RETR_TREE, CHAIN_APPROX_SIMPLE );
/// Draw contours
for( size_t i = 0; i< contours.size(); i++ )
{
Scalar color = Scalar( 0, 0, 255 );
Rect _boundingRect = boundingRect( contours[i] );
if( _boundingRect.height < 50 )
drawContours( src, contours, (int)i, color, 2 );
}
/// Show in a window
imshow( "Contours", src );
waitKey(0);
return(0);
}
after threshold you will get this binarized image
finally you will get your desired parts by contour analyzing
I have written a python equivalent code for the above
import numpy as np
import cv2
img = cv2.imread('New Bitmap Image.bmp')
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
ret,thresh = cv2.threshold(gray,127,255,cv2.THRESH_BINARY)
contours, hierarchy = cv2.findContours(thresh,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)
lt = len(contours)
for i in range (0,lt):
x,y,w,h = cv2.boundingRect(i)
if (h < 50):
cv2.drawContours(img,contours,i,(0,255,0),3)
cv2.imshow('output',img)
cv2.waitKey(0)
cv2.destroyAllWindows()
I get the following error
ERROR is
Traceback (most recent call last):
File "C:/Desktop/test.py", line 12, in <module>
x,y,w,h = cv2.boundingRect(i)
error: ..\..\..\..\opencv\modules\imgproc\src\contours.cpp:1895: error: (-215) points.checkVector(2) >= 0 && (points.depth() == CV_32F || points.depth() == CV_32S) in function cv::boundingRect
>>>
Asked: 2016-01-22 21:29:45 -0600
Seen: 2,308 times
Last updated: Jan 23 '16
@matman could you post your comment as an answer. i will add a sample code in your answer. i was just trying exactly the same method you explained.