On Ubuntu 20.04 it read image and display by using OpenCV 4.2

log_read_image.md

log read image

install opencv 4.2, matplotlib

sudo apt update
sudo apt -y upgrade
sudo apt install -y build-essential
sudo apt install -y python3-opencv
sudo apt install -y python3-matplotlib

error about missing opencv

chino@kafu:~$ python3 ./read_image.py 
Traceback (most recent call last):
  File "./read_image.py", line 4, in <module>
    import cv2
ModuleNotFoundError: No module named 'cv2'

error about missing matplotlib

matplotlib also can install through pip3.

chino@kafu:~$ python3 ./read_image.py 
Traceback (most recent call last):
  File "./read_image.py", line 5, in <module>
    from matplotlib import pyplot as plt
ModuleNotFoundError: No module named 'matplotlib'

error about missing image path

Traceback (most recent call last):
  File "./read_image.py", line 10, in <module>
    img_rgb = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
cv2.error: OpenCV(4.2.0) ../modules/imgproc/src/color.cpp:182: error: (-215:Assertion failed) !_src.empty() in function 'cvtColor'

read_image.py

#!/usr/bin/env python3
# read_image.py : test for reading image

import cv2
from matplotlib import pyplot as plt

#Read the image
filename1 = "/home/chino/sample.png"   #absolute path
img = cv2.imread(filename1, 1)
#plt.imshow(img)
img_rgb = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
plt.imshow(img_rgb) 
plt.show()