CODEWITHSUNDEEP
pythonc++numpyopencvvisual-c++
itsolidude
itsolidude

Reputation: 1249

Warp an image from given coordinates - OpenCV Python

Im learning OpenCV at the moment. The goal of this exercise is to take the 4 corner points of a Pokercard from a laying perspective and warping it flat in front of you.

As you can see I have the coordinates mapped out in pts1/ corners assigned correctly (It seems like that at least, after checking).

After outputting imgWarped it throws the error:

traceback (most recent call last):
  File "C:\Users\draco\PycharmProjects\Reader\main.py", line 101, in <module>
    imgWarped = cv2.warpPerspective(img,matrix,(width,height))
cv2.error: OpenCV(4.4.0) C:\Users\appveyor\AppData\Local\Temp\1\pip-req-build-95hbg2jt\opencv\modules\imgproc\src\imgwarp.cpp:3143: error: (-215:Assertion failed) _src.total() > 0 in function 'cv::warpPerspective'

The documentations online did not help me much resolving this problem. What does my error message actually mean and how does it happen? Is there a better practice?

Here is the code:

import cv2
import numpy as np

img = cv2.imread("Resources/cards.jpg")
width,height = 250,350
pts1 = np.float32([[124,161],[189,155],[200,231],[135,245]])
pts2 = np.float32([[0,0],[width,0],[width,height],[0,height]])
matrix = cv2.getPerspectiveTransform(pts1,pts2)
---Here is the error --> imgWarped = cv2.warpPerspective(img,matrix,(width,height))


cv2.imshow("Warped Img", imgWarped)
cv2.waitKey(0)

Upvotes: 0

Views: 1518

Answers (1)

Abdelsalam Hamdi
Abdelsalam Hamdi

Reputation: 515

I have used your code with my own image to regenerate the error, but it worked fine. You can either post to us your input image, or make sure the point you select is not larger than your image it self, coz I can see that you are hard coding the points

Upvotes: 1

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