How to remove non-straight diagonal lines from text image OpenCV?

Question

I have an image containing text but with non straight lines drawn on it.

I want to remove those lines without affecting/removing anything from the text.
For that I used Hough probabilistic transform:

import cv2
import numpy as np


def remove_lines(filename):
    img = cv2.imread(filename)
    gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
    edges = cv2.Canny(gray, 50, 200)
    lines = cv2.HoughLinesP(edges, rho=1, theta=1*np.pi/180,
                            threshold=100, minLineLength=100, maxLineGap=5)
    # Draw lines on the image
    for line in lines:
        x1, y1, x2, y2 = line[0]
        cv2.line(img, (x1, y1), (x2, y2), (0, 0, 255), 3)

    cv2.imwrite('result', img) 

The result was not as good as I expected:

The lines were not entirely detected (only some segments, the straight segments, of the lines were detected).
I did some adjustments on cv2.Canny and cv2.HoughLinesP parameters, but it didn't work too.

I also tried cv2.createLineSegmentDetector (Not available in the latest version of opencv due to license issue, so I had to downgrade opencv to version 4.0.0.21):

import cv2
import numpy as np
def remove_lines(filename):
    im = cv2.imread(filename)
    gray = cv2.cvtColor(im, cv2.COLOR_BGR2GRAY)
    # Create default parametrization LSD
    lsd = cv2.createLineSegmentDetector(0)

    # Detect lines in the image (Position 0 of the returned tuple are the
    # detected lines)
    lines = lsd.detect(gray)[0]

    # drawn_img = lsd.drawSegments(res, lines)
    for element in lines:
        if (abs(int(element[0][0]) - int(element[0][2])) > 70 or
                abs(int(element[0][1]) - int(element[0][3])) > 70):
            cv2.line(im, (int(element[0][0]), int(element[0][1])), (int(
                element[0][2]), int(element[0][3])), (0, 0, 255), 3)
    cv2.imwrite('lsd.jpg', im)  

The result was a bit better, but didn't detect the entire lines.

Any idea how to make the lines detection more efficient?

Answer 1

Use connectedComponentsWithStats to find out the longest two connected component in the image.