Get a single line representation for multiple close by lines clustered together in opencv

Question

I detected lines in an image and drew them in a separate image file in OpenCv C++ using HoughLinesP method. Following is a part of that resulting image. There are actually h

Answer 1

First off I want to note that your original image is at a slight angle, so your expected output seems just a bit off to me. I'm assuming you are okay with lines that are not 100% vertical in your output because they are slightly off on your input.

Mat image;
Mat binary = image > 125;  // Convert to binary image

// Combine similar lines
int size = 3;
Mat element = getStructuringElement( MORPH_ELLIPSE, Size( 2*size + 1, 2*size+1 ), Point( size, size ) );
morphologyEx( mask, mask, MORPH_CLOSE, element );

So far this yields this image:

These lines are not at 90 degree angles because the original image is not.

You can also choose to close the gap between the lines with:

Mat out = Mat::zeros(mask.size(), mask.type());

vector lines;
HoughLinesP(mask, lines, 1, CV_PI/2, 50, 50, 75);
for( size_t i = 0; i < lines.size(); i++ )
{
    Vec4i l = lines[i];
    line( out, Point(l[0], l[1]), Point(l[2], l[3]), Scalar(255), 5, CV_AA);
}

If these lines are too fat, I've had success thinning them with:

size = 15;
Mat eroded;
cv::Mat erodeElement = getStructuringElement( MORPH_ELLIPSE, cv::Size( size, size ) );
erode( mask, eroded, erodeElement );