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Computer Vision: Finding Lane Lines on the Road

Finding Lane Lines on the Road

The goals of this project are the following:

  • A pipeline that finds lane lines on the road

1. Pipeline describtion

My pipeline consisted of 6 steps.

  1. Mask the image to the region of interest using a polygon.
  2. Remove everything besides the white and yellow regions in the image
  3. Then I convert the image to grayscale
  4. Apply gaussian blur to remove image noise
  5. Apply the canny filter to the image (low: 50, high: 150 - 1:3)
  6. Detect lines using hough transformation (1 Pixel, 1 Radiant, 25 Thresh, 50 min line length and 150 max line gap)

To draw a single line on the left and right lanes, I modified the draw_lines() function by computing the slope m for every detected line. If the slope m is positive, it has to be the right lane, otherwise the left (in the code, left and right is named inverted - I forgot that y-axis is pointing down in image space :) ). Afterward, I check every line if m is in a plausible magnitude for a lane line (between 0.5 and 1). Then I take the average of m for the final left an right slope. I also compute b for both lanes. Having the complete line equations, I calculate the intersection with the horizontal top and button side of the ROI polygon and mark the points as end and beginning of the final lane lines.

2. Potential shortcomings with the current pipeline

One potential shortcoming would be a false detection if the lane marking disappears or a wrong image region is detected as lane marking. At the moment, this would dramatically affect the final lane marking.

3. Possible improvements

A possible improvement would be to track the right and left lane over time. Another potential improvement could be to add a low-pass filter to make the approach more robust against outlier.


A simple programming example on how to extract lane lines from images and videos.



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