How to fill the space in between the irregular lines?

I have two line (like a curve) with some gap in it and running parallel in a binary image. I need to fill the gaps without disturbing the original structure, so at the end I get two lines running parallel without any gaps(One long and one short). Also this principle should apply if the number of lines increases(eg: 4 lines in an image). My lines never intersect each others, always I have them running parallel. Its not a homework, its part of my project I'm working. I'm in middle of something and I cant think some algorithm to work in a generic way(If number of lines increases). Any idea guys?

Answer 1

[Image Analyst]

Did you ever think of an algorithm that goes across the image filling in the space between the first line and the last line as you stated? Something like this

[rows, columns] = size(binaryImage);
for col = 1 : columns
    thisColumn = binaryImage(:, col);
    topRow = find(thisColumn, 1, 'first');
    bottomRow = find(thisColumn, 1, 'last');
    binaryImage(topRow : bottomRow, col) = true;
end

It should work for the image you showed but I can't know whether it will work for images you did not show me, like images with tons of lines all over the place at weird angles and spacings, like you dropped a box of toothpicks on the ground.

[Hoa]

yes I did something similar to this using regionprops('extrema') function I did some morphological operation and labeled the object and used something like this

       x=[e(1,1).Extrema(4,1) e(2,1).Extrema(1,1)];
       y=[ e(1,1).Extrema(4,2) e(2,1).Extrema(1,2)];

After that I draw a line between those coordinates.

Here is another image (shown below), in this case I have to change my Extrema coordinates. I would like to know if there is some general technique or method to take care of whatever angles and spacing. I mostly have 3 lines (curves) broken and running parallel in an image. I also thought about finding the local direction of the skeleton and then trace it along that direction.