Detection of Hazmat labels (diamond shaped squares) using openCV

Question

I have to detect hazMat labels which are square shaped but depending upon the camera location they do not appear as perfect squares most of the time.

To have a look of hazmat labels and the background i have (the red color sign is hazMat sign)....please see the following link:

https://wiki.cc.gatech.edu/robocup/images/9/9b/Box3.jpg

Techniques i have tried so far:

1. Generalized hough transform: It didn't work because the shape keep changing depending upon the webcam location.

2. Color based segmentation and then Contour detection: It didn't work because the hazMat labels are of different color and many times the color difference between the background & Hazmat label is not too much.

3. Detection of contours having 4 point and eliminating small & very big contours: It also didn't work. The results are good and it is detecting quadrilateral except my Hazmat labels.

Kindly tell me, what other technique (or combination of techniques) i can try??

Answer 1

To detect the circle you need to execute the Canny algorithm to the Image processing part. then execute the cvt converstion to the MAT image At last implement the Houghcircle for circle. or go to the Find contours scenario.

This is what i have just detected. check the image .