Python Pillow - ImageOps.posterize() Function

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The PIL.ImageOps.posterize function is used to reduce the number of bits for each color channel in an image, effectively limiting the color palette.

Syntax

Following is the syntax of the function −

PIL.ImageOps.posterize(image, bits)

Parameters

Here are the details of this function parameters −

• image − The image to posterize.

• bits − The number of bits to keep for each channel (1-8). The value of bits determines the number of color levels for each channel, and it ranges from 1 to 8.

Return Value

The function returns a new image object where the input image has been posterized with the specified number of bits.

Examples

Example 1

Here’s an example that demonstrates how to create a new image with just 4-bits per channel.

from PIL import Image, ImageOps

# Open an image file
input_image = Image.open("Images/flowers.jpg")

# Posterize the image with 4 bits per channel
posterized_image = ImageOps.posterize(input_image, bits=4)

# Display the original and posterized images
input_image.show()
posterized_image.show()

Output

Input Image

Output Image

Example 2

Here's another example using the PIL.ImageOps.posterize function with a different image.

from PIL import Image, ImageOps

# Open an image file
input_image = Image.open("Images/Tajmahal_2.jpg")

# Posterize the image with 2 bits per channel
posterized_image = ImageOps.posterize(input_image, bits=2)

# Display the original and posterized images
input_image.show()
posterized_image.show()

Output

Input Image

Output Image

Example 3

In this example, the code performs posterization with different bit values to the image. And we use the Matplotlib to display the results.

from PIL import Image, ImageOps
import matplotlib.pyplot as plt

# Open the original image
original_image = Image.open('Images/flowers_1.jpg')

# Create subplots for original and posterized images
num_bits_list = [1, 2, 3, 4, 5, 6, 7, 8]

fig, axes = plt.subplots(3, 3, figsize=(10, 15))

# Display the original image
axes[0, 0].imshow(original_image)
axes[0, 0].set_title('Original Image')
axes[0, 0].axis('off')

# Perform posterization with different bit values and display the images
for idx, num_bits in enumerate(num_bits_list, start=1):
   posterized_image = ImageOps.posterize(original_image, bits=num_bits)
   
   # Display the posterized images
   axes[idx // 3, idx % 3].imshow(posterized_image)
   axes[idx // 3, idx % 3].set_title(f'Posterized {num_bits} bits')
   axes[idx // 3, idx % 3].axis('off')

plt.tight_layout()
plt.show()

Output