Basic geometric transformations – OpenCV 3.4 with python 3 Tutorial 12

by Sergio Canu February 12, 2018

import cv2
import numpy as np

img = cv2.imread("red_panda.jpg")
rows, cols, ch = img.shape

print("Height: ", rows)
print("Width: ", cols)

scaled_img = cv2.resize(img, None, fx=1/2, fy=1/2)

matrix_t = np.float32([[1, 0, -100], [0, 1, -30]])
translated_img = cv2.warpAffine(img, matrix_t, (cols, rows))

matrix_r = cv2.getRotationMatrix2D((cols/2, rows/2), 90, 0.5)
rotated_img = cv2.warpAffine(img, matrix_r, (cols, rows))

cv2.imshow("Original image", img)
cv2.imshow("Scaled image", scaled_img)
cv2.imshow("Translated image", translated_img)
cv2.imshow("Rotated image", rotated_img)
cv2.waitKey(0)
cv2.destroyAllWindows()

Files:

red_panda.jpg

4 Comments

Mustafa July 11, 2018 at 3:41 pm

hi sergio
my name ist mustafa im a student in germany and i have projekt with opencv. I saw your Tutorial 12 and would like to ask you how i can do the same with cv2.videocapture(0) .
i would appreciate it if you could help me with this.

Reply
1. Sergio Canu July 11, 2018 at 3:43 pm
  
  Hi Mustafa,
  it’s easy. It works in the same way but inside a loop, as for a video you need to process frame by frame.
  
  Here is the code for a video:
  
  [python]
  import cv2
  import numpy as np
  
  cap = cv2.VideoCapture(0)
  
  # Git first frame to take the size of frame
  _, frame = cap.read()
  rows, cols, ch = frame.shape
  
  print("Height: ", rows)
  print("Width: ", cols)
  
  while True:
  _, frame = cap.read()
  scaled_img = cv2.resize(frame, None, fx=1 / 2, fy=1 / 2)
  
  matrix_t = np.float32([[1, 0, -100], [0, 1, -30]])
  translated_img = cv2.warpAffine(frame, matrix_t, (cols, rows))
  
  matrix_r = cv2.getRotationMatrix2D((cols / 2, rows / 2), 90, 0.5)
  rotated_img = cv2.warpAffine(frame, matrix_r, (cols, rows))
  
  cv2.imshow("Original image", frame)
  cv2.imshow("Scaled image", scaled_img)
  cv2.imshow("Translated image", translated_img)
  cv2.imshow("Rotated image", rotated_img)
  
  key = cv2.waitKey(1)
  if key == 27:
  break
  
  cap.release()
  cv2.destroyAllWindows()
  [/python]
  
  Reply
Hanan Avraham March 26, 2019 at 9:38 am

Hi,
part of my final project to software engineer study we need to calculate Plant area.
we need to take photo of the plant each day, and calculate the area to check the Growth of the Plant.
do you have ant solution for me please..?
Thanks.

Reply
1. Sergio Canu March 27, 2019 at 9:06 pm
  
  Hi Hanan, it seems a simple task to achieve.
  You could create a mask by the color of the plant (you can see here how https://www.youtube.com/watch?v=SJCu1d4xakQ) and then calculate the area of the white part in the mask.
  
  Reply