CODEWITHSUNDEEP
androidopencv
Staff
Staff

Reputation: 933

Detect road lanes with android and opencv

i have problem with detection road lanes with my phone. i wrote some code for road lanes detection, but him not working for me. From camera get modifications from normal view to BGR colors and try use GausianBlur and Canny, but i think i not good draw lanes for detection. Maybe some people have another idea how detection road lanes with OpenCV?

Mat mYuv = new Mat(height + height / 2, width, CvType.CV_8UC1);
Mat mRgba = new Mat(height + height / 2, width, CvType.CV_8UC1);
Mat thresholdImage = new Mat(height + height / 2, width, CvType.CV_8UC1);
mYuv.put(0, 0, data);
Imgproc.cvtColor(mYuv, mRgba, Imgproc.COLOR_YUV420p2BGR, 4);
//convert to grayscale
Imgproc.cvtColor(mRgba, thresholdImage, Imgproc.COLOR_mRGBA2RGBA, 4);
// Perform a Gaussian blur (convolving in 5x5 Gaussian) & detect edges
Imgproc.GaussianBlur(mRgba, mRgba, new Size(5,5), 2.2, 2);
Imgproc.Canny(mRgba, thresholdImage, VActivity.CANNY_MIN_TRESHOLD, VActivity.CANNY_MAX_THRESHOLD);
Mat lines = new Mat();
double rho = 1;
double theta = Math.PI/180;
int threshold = 50;
//do Hough transform to find lanes
Imgproc.HoughLinesP(thresholdImage, lines, rho, theta, threshold, VActivity.HOUGH_MIN_LINE_LENGTH, VActivity.HOUGH_MAX_LINE_GAP);
for (int x = 0; x < lines.cols() && x < 1; x++){
    double[] vec = lines.get(0, x);
    double x1 = vec[0],
    y1 = vec[1],
    x2 = vec[2],
    y2 = vec[3];
    Point start = new Point(x1, y1);
    Point end = new Point(x2, y2);
    Core.line(mRgba, start, end, new Scalar(255, 0, 0), 3);
}

Upvotes: 0

Views: 1929

Answers (1)

timegalore
timegalore

Reputation: 731

This approach is fine and I've done something similar, not for road line detection but I did notice that it could be used for that purpose. Some comments:

Not sure why you do:

Imgproc.cvtColor(mRgba, thresholdImage, Imgproc.COLOR_mRGBA2RGBA, 4);

as 1. the comment say convert to greyscale, which is a single channel and 2. thresholdImage will get overwritten with the call to Canny later. You just need to dimension thresholdImage with:

thresholdImage = new Mat(mRgba.size(), CvType.CV_8UC1);

What are your parameter values to the call to Canny? I played about with mine considerably and ended up with values like: threshold1 = 441, threshold2 = 160, aperture = 3.

Likewise Imgproc.HoughLinesP: I use Imgproc.HoughLines rather than Imgproc.HoughLinesP with parameters: threshold = 80, minLen = 30, maxLen = 10.

Also have a look at:

for (int x = 0; x < lines.cols() && x < 1; x++){

&& x < 1 means you will only take the first line that the call to HoughLinesP returns. I'd suggest you remove this and use some other criteria to reduce the number of lines; for example, I was interesting in only horizontal and vertical lines so I used atan2 to calculate line angles and exclude those that deviate too much.

UPDATE

Here is how I get the angle of a line. Assuming coordinates of one point is (x1,y1) and the other (x2, y2) then to get the angle:

double lineAngle = Math.atan2(y2 - y1, x2 - x1);

this should return an angle in radians between -PI/2 and PI/2

With regard Canny parameters then I would experiment - I set up onTouch so that I could adjust the threshold values by touching certain parts of the screen to see the effects in realtime. Note that aperture is rather disappointing parameter: it seems to only like odd values 3, 5 and 7 and 3 is the best that I've found.

Something like in the onTouch method:

int w = mRgba.width();
int h = mRgba.height();

float x = event.getX();
float y = event.getY();

if ((x < w / 3) && (y < h / 2)) t1 += 20;
if ((x < w / 3) && (y >= h / 2)) t1 -= 20;
if ((x > 2 * w / 3) && (y < h / 2)) t2 += 20;
if ((x > 2 * w / 3) && (y >= h / 2)) t2 -= 20;

t1 and t2 being the threshold values passed to the Canny call.

Upvotes: 3

Related Questions