Python Open CV Homography giving unexpected results. Pleaase suggest what changes in code needed!!!!

asked 2019-07-10 19:37:51 -0500

updated 2019-07-11 03:04:28 -0500

berak gravatar image

Hi! I am doing homography in Python and am not getting expected Output. I am getting differen matrix

Here is my code's Google Colab link:-

https://colab.research.google.com/dri...

Here is basic Homography Link (just for your reference):-

https://www.learnopencv.com/image-ali...

In case you are not able to open Colab. Here is source code.

import cv2
import numpy as np

if __name__ == '__main__' :


    pts_src = np.array([[141.0, 131.0], [480.0, 159.0], [493.0, 630.0],[64.0, 601.0]])  

    pts_src=np.asarray(pts_src)                     #not needed actually
    pts_src = pts_src.astype('float32')              #not needed actually


    pts_dst = np.array([[318.0, 256.0],[534.0, 372.0],[316.0, 670.0],[73.0, 473.0]])
    pts_dst=np.asarray(pts_dst)                      #not needed actually
    pts_dst= pts_dst.astype('float32')               #not needed actually

    h, status = cv2.findHomography(pts_src, pts_dst,cv2.RANSAC, 5.0)

    # Wrap source image to destination based on homography

    print( h)
    print(len(h))
    print("------------Printing H------")
    print( status)
    print("------Printing Status-------------")
    print (status.ravel().tolist())
    print("--------------------")

    print("Source is multiplied first")

    #pts_src2 = np.array([[141.0, 131.0,1.0], [480.0, 159.0,1.0], [493.0, 630.0,1.0]])
    pts_dst2=np.array([[318.0, 256.0,1.0],[534.0, 372.0,1.0],[316.0, 670.0,1.0]]).transpose()

    print("----see---")
    print(+len(pts_dst2))
    pts_dst2=np.asarray(pts_dst2)                      #not needed actually
    pts_dst2= pts_dst2.astype('float32')               #not needed actually
    pts_dst2=np.asmatrix(pts_dst2)

    h=np.asmatrix(h)

    pts=np.dot( h, pts_dst2) 
    print(pts)


print("--------END-----------")

Output:-

 [ 1.46491654e-01  4.41418278e-01  1.61369294e+02]
 [-3.62463336e-04 -9.14274844e-05  1.00000000e+00]]
3
------------Printing H------
[[1]
 [1]
 [1]
 [1]]
------Printing Status-------------
[1, 1, 1, 1]
--------------------

Source is multiplied first

----see---
3
[[322.31218638 367.38950309 147.72051431]
 [320.95671889 403.80343648 503.41090271]
 [  0.86133122   0.77243355   0.82420517]]
--------END-----------
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