Rendering grayscale image

Question

Using this code :

import cv2
import matplotlib.pyplot as plt
%matplotlib inline 

plt.imshow(cv2.imread('badger.jpeg' , cv2.IMREAD_GRAYSCALE))

an image is read as greyscale and plotted to screen.

The image is plotted as :

This does not appear to be grayscale as there is colour that does not range form white to grey contained in the rendered image ?

My code is correct to read the image as grayscale using the IMREAD_GRAYSCALE parameter ?

The image is located at : https://sciencing.com/difference-between-badger-wolverine-8645505.html

Answer 1

The image is indeed flattened to grayscale if you use cv2.IMREAD_GRAYSCALE (you can test this using cv2.imread('im.jpg', cv2.IMREAD_GRAYSCALE).shape and cv2.imread('im.jpg').shape, and see that the former is a 3-d array and the latter is a 2-d array)

The issue is with the way matplotlib chooses to map your pixel values. When using plt.imshow(), it is using the default colormap (which is viridis, for some reason). This means pixel intensities / values will be mapped to the following:

You can change cmap to gray, in order to map them to the following:

plt.imshow(cv2.imread('badger.jpeg', cv2.IMREAD_GRAYSCALE), cmap='gray')

plt.show()