Chapter 22: Advanced Python Programming - Using the Pillow Library to Edit Images

22.1 Introduction

Image processing is a common requirement in many Python applications, including automation, web development, and data science. The Pillow library—an easy-to-use fork of the Python Imaging Library (PIL)—offers powerful tools for image manipulation such as resizing, cropping, filtering, and format conversion.

This chapter provides a practical introduction to Pillow, explaining its installation, basic operations, and advanced image editing techniques with code examples.

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22.2 Installing Pillow

To install Pillow, use the Python package installer:

pip install Pillow

You can now import the library using:

from PIL import Image

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22.3 Opening and Displaying Images

Opening an Image

from PIL import Image

img = Image.open("example.jpg")
img.show()

Getting Image Information

print(img.format)       # JPEG, PNG, etc.
print(img.size)         # (width, height)
print(img.mode)         # RGB, L (grayscale), etc.

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22.4 Saving Images

You can save an image in the same or different format:

img.save("new_image.png")

Convert before saving:

img.convert("L").save("grayscale.png")

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22.5 Resizing and Cropping

Resizing an Image

resized = img.resize((200, 300))
resized.show()

Thumbnail (Maintains Aspect Ratio)

img.thumbnail((100, 100))
img.show()

Cropping

box = (100, 100, 400, 400)  # (left, upper, right, lower)
cropped = img.crop(box)
cropped.show()

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22.6 Rotating and Flipping

Rotate an Image

rotated = img.rotate(90)  # degrees
rotated.show()

Flipping (Mirroring)

from PIL import ImageOps

flipped = ImageOps.mirror(img)
flipped.show()

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22.7 Changing Image Modes

Convert to Grayscale

gray = img.convert("L")
gray.show()

Convert to RGB

rgb_img = img.convert("RGB")

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22.8 Drawing on Images

Use the ImageDraw module to draw shapes and text:

from PIL import ImageDraw, ImageFont

draw = ImageDraw.Draw(img)
draw.rectangle([50, 50, 150, 150], outline="red")
draw.text((60, 60), "Hello", fill="blue")
img.show()

To use custom fonts:

font = ImageFont.truetype("arial.ttf", 20)
draw.text((60, 60), "Hi", font=font, fill="black")

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22.9 Applying Filters and Enhancements

Using Built-in Filters

from PIL import ImageFilter

blurred = img.filter(ImageFilter.BLUR)
sharpened = img.filter(ImageFilter.SHARPEN)
blurred.show()
sharpened.show()

Enhancing Images

from PIL import ImageEnhance

enhancer = ImageEnhance.Contrast(img)
enhanced = enhancer.enhance(1.5)  # 1.0 = original
enhanced.show()

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22.10 Batch Processing Images

Loop through a folder and apply operations:

import os

folder = "images"
for file in os.listdir(folder):
    if file.endswith(".jpg"):
        img_path = os.path.join(folder, file)
        img = Image.open(img_path)
        gray = img.convert("L")
        gray.save(f"gray_{file}")

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22.11 Creating New Images

You can create a blank image:

blank = Image.new("RGB", (200, 200), "white")
blank.show()

Then draw on it:

draw = ImageDraw.Draw(blank)
draw.line((0, 0, 200, 200), fill="blue", width=3)

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22.12 Real-Life Use Cases

• Thumbnails for Uploads: Resize and crop to standard dimensions.

• Watermarking: Overlay text on images.

• Grayscale Conversion: Useful in ML applications.

• Format Conversion: Convert images between JPEG, PNG, etc.

• Custom Captchas: Generate images with text and shapes.

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22.13 Summary

The Pillow library provides a versatile and accessible way to handle image editing tasks in Python. From basic format conversions to more advanced tasks like filtering, drawing, and batch editing, Pillow is a vital tool in the Python developer’s toolbox.

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22.14 Exercises

1. Write a Python script to open an image and convert it to grayscale.

2. Resize all .jpg images in a folder to 300x300 pixels and save them.

3. Draw a red circle and text "Sample" on a blank image.

4. Apply sharpen and contrast enhancement filters to an image.

5. Create a batch converter that transforms images from PNG to JPEG format.

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22.15 Review Questions

1. What is the purpose of the Pillow library?

2. How do you convert an image to grayscale using Pillow?

3. How can you draw shapes and text on an image?

4. What is the difference between resize() and thumbnail()?

5. Describe a practical use-case of Pillow in web development or automation.