Flipping an image vertically in Python without using flip() method

Question

I'm trying to flip an image vertically without using any default flip() or similar functions.I tried to iterate along the pixels and by using loops tried to reverse it so i can flip the image vertically.

image=cv2.imread('boat.jpg',1)
height,width,channel=image.shape
list1=[]
list2=[]
for i in range(height):
    for j in range(width):
        list1.append(image[i,j])
for a in range(len(list1)-1,-1,-1):
     list2.append(list1[a])
b=0
for i in range(height):
    for j in range(width):
        image[i,j]=list2[b]
        b+=1

But the flipped image is looking like this: https://ibb.co/KKVkd2d What am i doing wrong?

Answer 1

To flip vertically you have to reverse rows in array - first row has to be last, last row has to be first. You don't have to move pixels in rows.

import cv2
import numpy 

image = cv2.imread('boat.jpg', 1)

image = numpy.array(list(reversed(image)))

cv2.imshow('window', image)

cv2.waitKey(0)

---

BTW: if you want to flip horizontally then you have to reverse pixels in rows.

import cv2
import numpy 

image = cv2.imread('boat.jpg', 1)

image = numpy.array([list(reversed(row)) for row in image])

cv2.imshow('window', image)

cv2.waitKey(0)