CODEWITHSUNDEEP
pythonimagealgorithmopencvimage-processing
user2667455
user2667455

Reputation: 109

Image rotation angle opencv python

I am developing plate detection algorithm. I made plate localization and now new problem appear. I want to detect plate image rotation angle and rotate if necessary. But how to detect this ? I tried with cv2.HoughLinesP function, but result are as in attached image http://postimg.org/image/vis8errzn/

y = area.shape[0]
x = area.shape[1]
#############################################################################
#If necessary rotate image by angle detected with Hough transformation
gray = cv2.cvtColor(area,cv2.COLOR_BGR2GRAY)    
edges = cv2.Canny(gray,50,150,apertureSize = 3)
minLineLength = 10
maxLineGap = 30
lines = cv2.HoughLinesP(edges,1,math.pi/180,100,minLineLength,maxLineGap)
if(lines != None):
    for x1,y1,x2,y2 in lines[0]:
        cv2.line(gray,(x1,y1),(x2,y2),(0,255,0),2)
        a = ((y2-y1)*1.0)/((x2-x1)*1.0)
        print 'a = ', a
    print 'lines = ', lines

Upvotes: 0

Views: 3342

Answers (1)

Paul Seeb
Paul Seeb

Reputation: 6146

I am not positive what kind of "plate" you are referring to but I assume it is some planar object with notable features. In either case, here is an excellent tutorial by the folks at OpenCv explaining how to determine what I believe your question is asking:

http://docs.opencv.org/doc/tutorials/features2d/feature_homography/feature_homography.html

http://docs.opencv.org/3.0-beta/doc/py_tutorials/py_feature2d/py_feature_homography/py_feature_homography.html

The basic run down for this procedure is:

  • Given the image files for the plate in question (in the orientation you want to consider)
  • Detect feature points in both images
  • Use a descriptor on those feature points to give them "meaning"
  • Match the descriptors between the two images
  • Calculate the Homography between the two images (giving you the rotation matrix you are looking

for)

All of this can be done with opencv standard library functions.

Upvotes: -1

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