Why Does My Grayscale Image Appear in Color When Using Matplotlib\'s imshow()?

Resolving Display Issues for Grayscale Image in Matplotlib

In an attempt to display a grayscale image using Matplotlib's imshow(), you have encountered a situation where the image appears as a colormap instead. This can be frustrating when your objective is to draw on top of the image with color.

The Solution

The discrepancy arises because the imshow() function assigns a colormap to the image by default. To correct this, explicitly specify the cmap argument and set it to 'gray' or 'gray_r' to display grayscale or inverse grayscale, respectively:

<code class="python">import numpy as np
import matplotlib.pyplot as plt
from PIL import Image

# Open and convert the image to grayscale
fname = 'image.png'
image = Image.open(fname).convert("L")

# Convert the image to a matrix
arr = np.asarray(image)

# Display the grayscale image
plt.imshow(arr, cmap='gray', vmin=0, vmax=255) # Use 'gray_r' for inverse grayscale
plt.show()</code>

As this modified code demonstrates, specifying the colormap ensures that the image is rendered correctly as grayscale. You can now proceed with your intended task of drawing on top of the image with color.

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