Incorrect image orientation when drawing a line with cv2.line

Question

I want to draw a line from top left corner to the bottom right corner on an image.
The image is horizontal and:

print(size)

returns:

(203, 248)

With my code I am expecting a diagonal line from pixel (0,0) to pixel (203, 248). However I am getting diagonal line from pixel (0,0) to pixel (248, 203) which is outside the image boundary (sic!).
I suppose the cv2.line method rotates the image somehow, can anyone advise?

Here is my code:

import cv2

image_1 = cv2.imread('profilowe.jpeg',0)
size = image_1.shape
print(size)
cv2.line(image_1,(0,0),image_1.shape,255,1,16)

cv2.imshow('image',image_1)
cv2.waitKey(0)
cv2.destroyAllWindows()

Asked By: KorwinNaSloniu

||

Source

Answer 1

This happens because while NumPy indexes arrays based on a row-first principle (i.e. your shape is (rows, columns)), OpenCV indexes based on (x, y) co-ordinates, meaning the axes are flipped. This can be annoying to deal with, but this should fix your issue:

Try changing:

cv2.line(image_1, (0,0), image_1.shape, 255, 1, 16)

to

cv2.line(image_1, (0,0), image_1.shape[::-1], 255, 1, 16)

The [::-1] flips the tuple to become (248, 203), and your line should look fine now.

Answered By: mxbi

Incorrect image orientation when drawing a line with cv2.line

Question:

Answers: