Line Segment Detector demo

An example using the cv.LineSegmentDetector class.

Sources:

https://github.com/opencv/opencv/blob/3.3.1/samples/cpp/lsd_lines.cpp

Input image
Preprocess
LSD detectors
Result 1
Result 2
Compare

Input image

img = cv.imread(fullfile(mexopencv.root(),'test','building.jpg'), 'Grayscale',true);

Preprocess

Apply canny edge detector

if false
    img = cv.Canny(img, [50 200], 'ApertureSize',5);
end

LSD detectors

Create two LSD detectors with standard and no refinement.

lsd1 = cv.LineSegmentDetector('Refine','Standard');
lsd2 = cv.LineSegmentDetector('Refine','None');

Detect the lines both ways

tic, lines1 = lsd1.detect(img); toc
tic, lines2 = lsd2.detect(img); toc

Elapsed time is 0.102855 seconds.
Elapsed time is 0.037938 seconds.

Result 1

Show found lines with standard refinement

drawnLines1 = lsd1.drawSegments(img, lines1);
imshow(drawnLines1), title('Standard refinement')

Result 2

Show found lines with no refinement

drawnLines2 = lsd2.drawSegments(img, lines2);
imshow(drawnLines2), title('No refinement')

Compare

[h,w,~] = size(img);
[comparison,mis_count] = lsd1.compareSegments([w,h], lines1, lines2);
imshow(comparison), title(sprintf('Mismatch = %d', mis_count))