如何用枕頭在Python中執行基本圖像處理操作？

Pillow 是一個強大且易於使用的Python 圖像處理庫，1. 首先通過pip install pillow 安裝並導入庫；2. 使用Image.open() 打開圖像，save() 保存圖像，格式由文件擴展名自動識別；3. resize() 可調整圖像大小但不保持寬高比，thumbnail() 在保持寬高比的同時創建縮略圖；4. crop() 接受(left, upper, right, lower) 元組進行裁剪；5. rotate() 按角度逆時針旋轉圖像，expand=True 可保留完整圖像，transpose() 可實現水平或垂直翻轉；6. convert('L') 轉為灰度圖，convert('1') 轉為1位黑白圖；7. 使用ImageFilter.BLUR 等應用模糊、銳化、邊緣檢測等濾鏡；8. ImageEnhance.Brightness、Contrast、Color 分別用於調整亮度、對比度和飽和度；9. 可通過size、mode、format 等屬性獲取圖像信息；10. paste() 可將一個圖像疊加到另一個圖像上，支持透明通道。 Pillow 使得圖像處理操作簡潔高效，適合自動化縮略圖生成、格式轉換和機器學習預處理等任務。

Pillow (PIL Fork) is a powerful and easy-to-use library for image processing in Python. It allows you to perform a wide range of basic operations like opening, saving, resizing, cropping, rotating, filtering, and color manipulation. Here's how to handle common image processing tasks using Pillow.

1. Install and Import Pillow

First, install Pillow if you haven't already:

 pip install pillow

Then import it in your script:

 from PIL import Image, ImageFilter, ImageEnhance

2. Open and Save Images

To load an image from a file:

 img = Image.open('input.jpg')

To save it in a different format or location:

 img.save('output.png')

Pillow automatically detects the format based on the file extension.

3. Basic Image Operations

Resize an Image

Use resize() to change dimensions. Pass a tuple (width, height):

 resized_img = img.resize((800, 600))
resized_img.save('resized.jpg')

⚠️ Note: resize() doesn't maintain aspect ratio by default. To preserve it, calculate dimensions manually or use thumbnail() .

Create a Thumbnail (Preserves Aspect Ratio)

 img_copy = img.copy() # Always work on a copy
img_copy.thumbnail((800, 600)) # Modifies in place, respects aspect ratio
img_copy.save('thumbnail.jpg')

Crop an Image

Specify a bounding box as (left, upper, right, lower):

 cropped_img = img.crop((100, 100, 400, 400)) # Crops a 300x300 region
cropped_img.save('cropped.jpg')

Rotate an Image

Rotate by a given angle (counterclockwise):

 rotated_img = img.rotate(45, expand=True) # expand=True keeps the whole image
rotated_img.save('rotated.jpg')

You can also flip or mirror:

 flipped_img = img.transpose(Image.FLIP_LEFT_RIGHT) # Horizontal flip
# flipped_img = img.transpose(Image.FLIP_TOP_BOTTOM) # Vertical flip
flipped_img.save('flipped.jpg')

4. Color and Mode Manipulation

Convert between color modes (eg, RGB, grayscale, black & white):

 gray_img = img.convert('L') # Grayscale
gray_img.save('grayscale.jpg')

bw_img = img.convert('1') # 1-bit black and white (dithered)
bw_img.save('black_white.jpg')

5. Apply Filters and Enhancements

Apply Built-in Filters

Use ImageFilter module:

 # Blur
blurred_img = img.filter(ImageFilter.BLUR)

# Sharpen
sharpened_img = img.filter(ImageFilter.SHARPEN)

# Edge enhancement
edges_img = img.filter(ImageFilter.FIND_EDGES)

blurred_img.save('blurred.jpg')

Adjust Brightness, Contrast, Saturation

Use ImageEnhance classes:

 enhancer = ImageEnhance.Brightness(img)
bright_img = enhancer.enhance(1.5) # Increase brightness by 50%
bright_img.save('bright.jpg')

# Similarly for contrast
enhancer = ImageEnhance.Contrast(img)
contrast_img = enhancer.enhance(2.0) # Double contrast
contrast_img.save('high_contrast.jpg')

# For color saturation
enhancer = ImageEnhance.Color(img)
color_img = enhancer.enhance(1.5) # Boost color
color_img.save('color_enhanced.jpg')

6. Get Image Information

You can inspect basic image properties:

 print("Size:", img.size) # (width, height)
print("Mode:", img.mode) # eg, RGB, L
print("Format:", img.format) # eg, JPEG, PNG
print("Width:", img.width)
print("Height:", img.height)

7. Combine Images (Optional)

Paste one image onto another:

 base_img = Image.open('background.jpg')
overlay = Image.open('logo.png').resize((100, 100))

# Paste overlay at position (50, 50)
base_img.paste(overlay, (50, 50), overlay) # Third arg for alpha mask
base_img.save('combined.png')

Summary

Pillow makes basic image processing simple and intuitive. Key points:

• Use Image.open() and .save() for loading and saving.
• .resize() , .crop() , .rotate() , .transpose() for geometry changes.
• .convert() for color mode changes.
• ImageFilter and ImageEnhance for visual effects.
• Always work on copies to avoid modifying the original.

With these tools, you can automate common image tasks like thumbnails, format conversion, and preprocessing for machine learning.

Basically just a few lines for most operations — but powerful when chained together.

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