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There are two types of picture mirroring transformation: horizontal mirror image and vertical mirror image.

Horizontal mirroring uses the vertical center line of the picture as the axis to swap the pixels of the picture, that is, to swap the left half and the right half of the picture.

Vertical mirroring takes the horizontal center line of the image as the axis, and swaps the upper half of the image with the lower part.

Transformation principle:

Set the width of the image be width and the length be height. (x, y) is the transformed coordinates, (x0, y0) is the coordinates of the original picture.

Horizontal mirror transformation

Forward mapping

Inverse transformation

Backward mapping

Vertical mirror transformation

Inverse transformation

We take the vertical transformation as an example.

Code path:

/home/pi/Yahboom_Project/1.OpenCV_course/02Geometric_transformation/04_Picture_mirroring.ipynb

import cv2
import numpy as np
img = cv2.imread('yahboom.jpg',1)
#cv2.imshow('src',img)
imgInfo = img.shape
height = imgInfo[0]
width = imgInfo[1]
deep = imgInfo[2]
newImgInfo = (height*2,width,deep)
dst = np.zeros(newImgInfo,np.uint8)#uint8 
for i in range(0,height):
    for j in range(0,width):
        dst[i,j] = img[i,j]
        #x y = 2*h - y -1
        dst[height*2-i-1,j] = img[i,j]
for i in range(0,width):
    dst[height,i] = (0,0,255) #BGR

#bgr8 to jpeg format
import enum
import cv2
def bgr8_to_jpeg(value, quality=75):
    return bytes(cv2.imencode('.jpg', value)[1])

import ipywidgets.widgets as widgets
image_widget1 = widgets.Image(format='jpg', )
# image_widget2 = widgets.Image(format='jpg', )
# create a horizontal box container to place the image widget next to eachother
# image_container = widgets.HBox([image_widget1, image_widget2])
# display the container in this cell's output
display(image_widget1)
#display(image_widget2)
image_widget1.value = bgr8_to_jpeg(dst)

As shown below.