Lane detection system and method

1. A method for detecting a lane within a road image captured by a camera having a field of view in front of a vehicle traveling along a road having a lane marker, comprising the steps of:

identifying, within the road image, a reference point located at a reference-point height, with respect to the bottom of the road image, determined by an angle-of-view of the camera in a plane orthogonal to the road;

adjusting the reference-point height according to a location of a vanishing point in the road image to obtain an adjusted reference-point height;

determining a first height as a first fraction of the adjusted reference-point height;

determining a second height equal to a sum of the adjusted reference point height and a second fraction of a height of the road image, each of the first fraction and second fraction being positive and less than one;

processing the road image to identify a lane candidate within a lane-existing region of the road image, the lane-existing region having (i) a first subregion having the first height with respect to the bottom of the road image, (ii) a second subregion having the second height with respect to the bottom of the road image, and (iii) the reference point;

verifying the lane candidate as a true lane candidate when a minimum distance between (a) a line fit to a portion of the lane candidate in the first subregion and (b) the predetermined reference point is less than a neighborhood distance; and

extending the true lane candidate into the second subregion to form a detected lane marker demarcating the lane marker.

2. The method of claim 1 , the step of processing comprising:

identifying a ridge feature within the road image to generate a ridge-feature image; and

identifying, within the ridge-feature image, a plurality of lines each at least partially overlapping the ridge feature.

3. The method of claim 2 , the plurality of lines being mutually non-collinear, and further comprising conjoining the plurality of lines to identify the lane candidate.

4. The method of claim 3 , the step of conjoining comprising, in a blank image having a plurality of pixels each having (i) the same pixel value and (ii) a pixel coordinate in the blank image:

changing the pixel values of a plurality of lane-candidate pixels, a lane-candidate pixel being a pixel having pixel coordinates corresponding to one of the plurality of lines;

executing a morphological operator on the plurality lane-candidate lane pixels.

5. The method of claim 2 , the step of identifying a ridge feature comprising:

for each of a plurality of locations of the road image:

computing a first horizontal image gradient partially based on a first image intensity representative of a first image region entirely to the left of the location;

computing a second horizontal image gradient partially based on a second image intensity representative of a second image region entirely to the right of the location; and

determining whether the location is part of a ridge feature based on the first horizontal image gradient and the second horizontal image gradient.

6. The method of claim 5 , further comprising determining, based on a vertical position of the location, a horizontal width of at least one of (a) the first image region, (b) the second image region, and (c) the ridge feature.

7. The method of claim 5 , further comprising applying a continuity threshold operation to the ridge feature image to disqualify ridge features not corresponding to a lane marker.

8. The method of claim 7 , each ridge feature being formed of a plurality of candidate ridge pixels, the continuity threshold operation having a threshold according to a minimum number of spatially-connected candidate ridge pixels in each candidate ridge feature.

9. The method of claim 2 , one of the plurality of lines being fit to a plurality of near control points in the ridge-feature image corresponding to the lane candidate, the near control points being in a near subregion of the ridge-feature image corresponding to the first subregion of the road image.

10. The method of claim 1 , the step of extending further comprising, for each true lane candidate,

identifying, in the second subregion, a far control point corresponding to the true lane candidate; and

fitting a curve to the far control point and a plurality of near control points located in the first subregion and corresponding to the true lane candidate.

11. A lane detection system for detecting a lane within a road image captured along a road having a lane marker comprising:

a non-volatile memory storing machine-readable instructions; and

an image processor communicatively coupled to the memory, capable of receiving the road image; and, when executing the machine-readable instructions, capable of:

identifying, within the road image, a reference point located at a reference-point height, with respect to the bottom of the road image, determined by an angle-of-view of the camera in a plane orthogonal to the road;

adjusting the reference-point height according to a location of a vanishing point in the road image to obtain an adjusted reference-point height;

determining a first height as a first fraction of the adjusted reference-point height;

determining a second height equal to a sum of the adjusted reference point height and a second fraction of a height of the road image, each of the first fraction and second fraction being positive and less than one;

(i) processing the road image to identify a lane candidate within a lane-existing region of the road image, the lane-existing region having (i) a first subregion having the first height with respect to the bottom of the road image, (ii) a second subregion having the second height with respect to the bottom of the road image, and (iii) the reference point,

(ii) verifying the lane candidate as a true lane candidate when a minimum distance between (a) a line fit to a portion of the lane candidate in the first subregion and (b) the predetermined reference point is less than a neighborhood distance; and

(iii) extending the true lane candidate into the second subregion to form a detected lane marker demarcating the lane marker.

12. The system of claim 11 , the image processor being further capable of, when executing the machine-readable instructions to process the road image:

identifying a ridge feature within the road image to generate a ridge-feature image; and

identifying, within the ridge-feature image, a plurality of lines each at least partially overlapping the ridge feature.

13. The system of claim 12 , the plurality of lines being mutually non-collinear, and the image processor being further capable of, when executing the machine-readable instructions, conjoining the plurality of lines to identify the lane candidate.

14. The system of claim 13 , the image processor being further capable of, when executing the machine-readable instructions to conjoin the plurality of lines: executing a morphological operator on the plurality of lines to form the lane candidate.

15. The system of claim 12 , the image processor being further capable of, when executing the machine-readable instructions to identify a ridge feature:

computing a first horizontal image gradient partially based on a first image intensity representative of a first image region entirely to the left of the location;

computing a second horizontal image gradient partially based on a second image intensity representative of a second image region entirely to the right of the location; and

determining whether the location is part of a ridge feature based on the first horizontal image gradient and the second horizontal image gradient.

16. The system of claim 15 , the image processor being further capable of, when executing the machine-readable instructions, determining, based on a vertical position of the location, a horizontal width of at least one of (a) the first image region, (b) the second image region, and (c) the ridge feature.

17. The system of claim 15 , the image processor being further capable of, when executing the machine-readable instructions, applying a continuity threshold operation to the ridge feature image to disqualify ridge features not corresponding to a lane marker.

18. The system of claim 17 , each ridge feature being formed of a plurality of candidate ridge pixels, the continuity threshold operation having a threshold according to a minimum number of spatially-connected candidate ridge pixels in each candidate ridge feature.

19. The system of claim 12 , one of the plurality of lines being fit to a plurality of near control points in the ridge-feature image corresponding to the lane candidate, the near control points being in a near subregion of the ridge-feature image corresponding to the first subregion of the road image.

20. The system of claim 12 , the predetermined reference point in the road image being a vanishing point of the road image.

21. The system of claim 11 , the image processor being further capable of, when executing the machine-readable instructions to extend the true lane candidate:

identifying, in the second subregion, a far control point corresponding to the true lane candidate; and

fitting a curve to the far control point and a plurality of near control points located in the first subregion and corresponding to the true lane candidate.

22. The system of claim 21 , the far control point being adjacent to a pixel of the true lane candidate in the first subregion.

23. The method of claim 1 , the first fraction being equal to three-quarters, the second fraction being equal to one-sixteenth.

24. The system of claim 11 , the first fraction being equal to three-quarters, the second fraction being equal to one-sixteenth.

25. The method of claim 4 , the morphological operator being a closing operator.

26. The system of claim 14 , the morphological operator being a closing operator.