automatic road sign recognition - stanford universitycq536cq5284/zheng_traffic_sig… · automatic...
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Objective
● Automatically recognition road sign in the image● Separate stop sign and yield sign
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Algorithm
● R,G,B domain thresholding● Remove small and large regions● Dilation to connect fragmented part of the signs● Remove regions whose major / minor axis ratio
is too large● Compute filling ratio the separate two signs
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Algorithm
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Algorithm
● R,G,B domain thresholding– Thresholding on G/R, B/R ratio (instead on G, B
itself)
– More robust to changing lighting condition
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Algorithm
● Remove small and large region– Small region: noise, vehicle tail light cover, road
pavement, etc
– Large region: large red background (building wall)
Original image Stop sign and part of the vehicle red tail light cover is segmented out
Only stop sign remained (after dilation) when small object is removed
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Algorithm
● Remove region with large major/minor axis ratio– Road sign, ratio is close to 1
A red pole is alsoselected. It will beremoved later onsince its ratio is large,
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Algorithm
● Filling ratio– Stop sign tend to have larger filling ratio than yield
sign
Stop sign, filling ratio 0.85
yield sign, filling ratio 0.59
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Data Set
Total Image Stop Sign Image Yield sign Image
65 52 13
Divide into training and testing groups:
Total Image Stop Sign Image Yield sign Image
45 37 8
Training group:
Testing group:
Total Image Stop Sign Image Yield sign Image
20 15 5
Total:
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Thresholds
● Training data is used to choose the thresholds of the algorithm– For each image, manually select an area on the
traffic sign, record the properties.
– Properties selected: minR, meanR, maxR, minG/R, meanG/R, maxG/R, minB/R, meanB/R, maxB/R
– Select thresholds so that traffic signs in most of the training image can be correctly segmented out.
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Thresholds
● Selected thresholds:– MinR: 65, maxR: 255, minG/B: 0, maxG/B: 0.7,
minB/R: 0, maxB/R: 0.7
– Minimum size: 40 pixels
– Maximum size: 400000 pixels
– Filling ratio threshold: 0.7
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Results
● The algorithm is applied on all images and testing images:
● All images:
total Stop sign Yield sign
65 52 13
detected 54 (83.0%) 43 (82.7%) 11 (84.6%)
missed 11 (16.9%) 9 (17.3%) 2 (15.4%)
False detection*
10 (15.4%) 8 (15.3%) 2 (15.3%)
* False detection means the traffic sign in the image is identify, however, the algorithm also picks up other region in the image as traffic sign
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Results
● Testing images:
total Stop sign Yield sign
20 15 5
detected 16 (80.0%) 13 (86.7%) 3 (60.0%)
missed 4 (20.0%) 2 (13.3%) 2 (40.0%)
False detection*
2 (10.0%) 2 (13.3%) 0 (0%)
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Examples
● Stop sign detection
original after rgb thresholding after removing small regions
after dilation finalfilling ratio0.82
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Examples
● Yield sign detection:
original after rgb thresholding
after removing small regions final, filling ratio 0.60
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Conclusion
● This algorithm achieved about 80% correct detection rate in testing image and in whole image group as well.
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Limitation
● Fail to recognize sign when it is connect with other red object
● Fail to work when it is too dark
stop sign not recognized since itis connected with a red pole
stop sign not segmented out sinceit is too dark