OpenCV2 - Narrow Rectangles found using SimpleBlobDetector, but can't extract the angle

Question

I'm trying to get the angle of the middle line in a domino. SimpleBlobDetector can find it, but it gives me an angle value of -1. Does anyone know why that can be? and how can i fix that still using SimpleBlobDetector? and if SimpleBlobDetector is not an option, what else can i do to find the center and angle of these lines?

import numpy as np
import cv2
import os
import time
#from matplotlib import pyplot as plt

def main():
    capWebcam = cv2.VideoCapture(0)         # declare a VideoCapture object and associate to webcam, 0 => use 1st webcam

    params = cv2.SimpleBlobDetector_Params()
    params.filterByCircularity = True
    params.minCircularity = 0.73

    params2 = cv2.SimpleBlobDetector_Params()
    params2.filterByInertia = True
    params2.maxInertiaRatio = 0.3

                    # show original resolution
    print "default resolution = " + str(capWebcam.get(cv2.CAP_PROP_FRAME_WIDTH)) + "x" + str(capWebcam.get(cv2.CAP_PROP_FRAME_HEIGHT))

    capWebcam.set(cv2.CAP_PROP_FRAME_WIDTH, 320.0)              # change resolution to 320x240 for faster processing
    capWebcam.set(cv2.CAP_PROP_FRAME_HEIGHT, 240.0)
    capWebcam.set(cv2.CAP_PROP_FPS, 1)


                                            # show updated resolution
    print "updated resolution = " + str(capWebcam.get(cv2.CAP_PROP_FRAME_WIDTH)) + "x" + str(capWebcam.get(cv2.CAP_PROP_FRAME_HEIGHT))

    if capWebcam.isOpened() == False:               # check if VideoCapture object was associated to webcam successfully
        print "error: capWebcam not accessed successfully\n\n"      # if not, print error message to std out
        os.system("pause")                                          # pause until user presses a key so user can see error message
        return                                                      # and exit function (which exits program)
    # end if

    while cv2.waitKey(1) != 27 and capWebcam.isOpened():            # until the Esc key is pressed or webcam connection is lost
        blnFrameReadSuccessfully, img = capWebcam.read()            # read next frame

        if not blnFrameReadSuccessfully or img is None:     # if frame was not read successfully
            print "error: frame not read from webcam\n"             # print error message to std out
            os.system("pause")                                      # pause until user presses a key so user can see error message
            break                                                   # exit while loop (which exits program)

        det = cv2.SimpleBlobDetector_create(params)
        det2 = cv2.SimpleBlobDetector_create(params2)


        gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)



        time.sleep(0.1)
        keypts = det.detect(gray)
        time.sleep(0.1)
        keypts2 = det2.detect(gray)

        print len(keypts)
        print len(keypts2)

        for l in keypts2:
            print l.pt
            print l.angle                




        time.sleep(0.3)
        imgwk = cv2.drawKeypoints(gray, keypts, img,color= (200,0,139),flags=2)

        time.sleep(0.1)
        imgwk2 = cv2.drawKeypoints(img, keypts2, gray,color= (200,0,139),flags=2)



        cv2.namedWindow("img", cv2.WINDOW_AUTOSIZE)           # or use WINDOW_NORMAL to allow window resizing

        cv2.imshow("img", img)

                              # hold windows open until user presses a key

    cv2.destroyAllWindows()

    return


###################################################################################################
if __name__ == "__main__":
    main()

score 0 · Answer 1 · edited May 23 '17 at 12:10

0

I'm not sure if SimpleBlob detector is the best for this, but have you looked at

Detect centre and angle of rectangles in an image using Opencv

It seems quite similar to you question, and seems to do very well at identifying the angle of the rectangles

edited May 23 '17 at 12:10

Community

1
1

answered Mar 29 '17 at 10:27

precipitation

1
1

I'll give this a try. Thanks :D – Luli Mar 29 '17 at 10:34
Do you have any idea how to convert this: ' cv::RotatedRect rotatedRect = cv::minAreaRect(contours[i]); // read points and angle cv::Point2f rect_points[4]; rotatedRect.points( rect_points ); float angle = rotatedRect.angle; // angle // read center of rotated rect cv::Point2f center = rotatedRect.center; // center' to python? – Luli Mar 29 '17 at 11:06

OpenCV2 - Narrow Rectangles found using SimpleBlobDetector, but can't extract the angle

1 Answers1