README for Flask Image Compression API with Pillow

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Overview

This project is a Flask-based API for compressing, rotating, and handling image files. It utilizes the Pillow library (a fork of the Python Imaging Library) to perform operations like resizing and correcting image orientations based on EXIF metadata.

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Key Features

1. Image Orientation Correction:

   • Automatically adjusts image orientation using EXIF metadata to ensure the correct display.

2. Rotation:

   • Provides an option to rotate images by a specified angle.

3. Compression:

   • Compresses images while maintaining their quality within specified dimensions.

4. Blank Image Generator:

   • Creates blank images of user-defined dimensions.

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Dependencies

• Flask: For building the API endpoints.
• Pillow: For image manipulation.
• io: For handling input/output streams.

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Setup Instructions

1. Create and Activate a Virtual Environment:

   • Create:

     python -m venv venv

   • Activate:
     • Windows:

       venv\Scripts\activate

     • macOS/Linux:

       source venv/bin/activate

2. Install Dependencies:

   pip install flask pillow

3. Run the Application:

   python app.py

4. API Endpoints:

   • Compress Image: /compress (POST)
   • Generate Blank Image: /blank_image (GET)

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Using the Pillow Library

Pillow provides an easy-to-use API for image manipulation. Here's how it's used in this project:

1. EXIF Orientation Correction:

   exif = img._getexif()
   if exif:
       orientation = exif.get(274)  # 274 is the EXIF tag for Orientation
       if orientation == 3:
           img = img.rotate(180, expand=True)  # Upside down
       elif orientation == 6:
           img = img.rotate(270, expand=True)  # Clockwise 270
       elif orientation == 8:
           img = img.rotate(90, expand=True)   # Clockwise 90

2. Image Rotation:

   img = img.rotate(rotation_angle, expand=True)  # Custom rotation if specified

3. Image Resizing:

   img.thumbnail((new_width, new_height))  # Resize while maintaining aspect ratio

4. Saving the Image:

   img.save(output_stream, format=file_extension)  # Save manipulated image to output stream

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Code Explanation

Compress Image Logic

• Input: A file stream containing an image.
• Process:
  • Identify if the file is an image.
  • Correct its orientation using EXIF data.
  • Resize it to specified dimensions while maintaining aspect ratio.
  • Optionally rotate the image.
• Output: A compressed image saved to the output stream.

Blank Image Generator

• Input: Width and height via query parameters.
• Process: Creates a blank white image of the specified dimensions.
• Output: A blank image file.

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API Examples

Compress Image

curl -X POST -F "file=@input_image.jpg" -F "rotation_angle=90" http://127.0.0.1:5000/compress -o compressed_image.jpg

Generate Blank Image

curl "http://127.0.0.1:5000/blank_image?width=500&height=500" -o blank_image.jpg

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Troubleshooting

1. Unexpected Errors with Pillow:

   • Ensure Pillow is properly installed.
   • Verify the image format is supported (e.g., JPG, PNG).

2. Image Orientation Not Corrected:

   • Ensure the image contains valid EXIF data (not all images may have EXIF tags).
   • Check if the EXIF orientation tag is properly handled.

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References

• Pillow Documentation
• ExifTags in Pillow

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