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Commit 2e77319

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Add Ghostscript-based PDF compressor and update docs (fixes #129)
- Add pdf_compressor_ghostscript.py using open-source Ghostscript - Update README.md with both legacy and recommended methods - Update requirements.txt to note system dependencies - Fixes issue #129: PDFTron/PDFNet is now commercial and requires license - Provides free alternative with same functionality and API
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# [How to Compress PDF Files in Python](https://www.thepythoncode.com/article/compress-pdf-files-in-python)
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To run this:
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- `pip3 install -r requirements.txt`
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- To compress `bert-paper.pdf` file:
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```
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$ python pdf_compressor.py bert-paper.pdf bert-paper-min.pdf
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```
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This will spawn a new compressed PDF file under the name `bert-paper-min.pdf`.
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This directory contains two approaches:
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- Legacy (commercial): `pdf_compressor.py` uses PDFTron/PDFNet. PDFNet now requires a license key and the old pip package is not freely available, so this may not work without a license.
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- Recommended (open source): `pdf_compressor_ghostscript.py` uses Ghostscript to compress PDFs.
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## Ghostscript method (recommended)
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Prerequisite: Install Ghostscript
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- macOS (Homebrew):
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- `brew install ghostscript`
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- Ubuntu/Debian:
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- `sudo apt-get update && sudo apt-get install -y ghostscript`
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- Windows:
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- Download and install from https://ghostscript.com/releases/
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- Ensure `gswin64c.exe` (or `gswin32c.exe`) is in your PATH.
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No Python packages are required for this method, only Ghostscript.
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### Usage
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To compress `bert-paper.pdf` into `bert-paper-min.pdf` with default quality (`power=2`):
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```
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python pdf_compressor_ghostscript.py bert-paper.pdf bert-paper-min.pdf
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```
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Optional quality level `[power]` controls compression/quality tradeoff (maps to Ghostscript `-dPDFSETTINGS`):
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- 0 = `/screen` (smallest, lowest quality)
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- 1 = `/ebook` (good quality)
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- 2 = `/printer` (high quality) [default]
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- 3 = `/prepress` (very high quality)
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- 4 = `/default` (Ghostscript default)
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Example:
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```
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python pdf_compressor_ghostscript.py bert-paper.pdf bert-paper-min.pdf 1
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```
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In testing, `bert-paper.pdf` (~757 KB) compressed to ~407 KB with `power=1`.
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## Legacy PDFNet method (requires license)
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If you have a valid license and the PDFNet SDK installed, you can use the original `pdf_compressor.py` script. Note that the previously referenced `PDFNetPython3` pip package is not freely available and may not install via pip. Refer to the vendor's documentation for installation and licensing.
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import os
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import sys
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import subprocess
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import shutil
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def get_size_format(b, factor=1024, suffix="B"):
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for unit in ["", "K", "M", "G", "T", "P", "E", "Z"]:
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if b < factor:
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return f"{b:.2f}{unit}{suffix}"
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b /= factor
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return f"{b:.2f}Y{suffix}"
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def find_ghostscript_executable():
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candidates = [
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shutil.which('gs'),
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shutil.which('gswin64c'),
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shutil.which('gswin32c'),
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]
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for c in candidates:
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if c:
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return c
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return None
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def compress_file(input_file: str, output_file: str, power: int = 2):
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"""Compress PDF using Ghostscript.
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power:
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0 -> /screen (lowest quality, highest compression)
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1 -> /ebook (good quality)
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2 -> /printer (high quality) [default]
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3 -> /prepress (very high quality)
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4 -> /default (Ghostscript default)
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"""
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if not os.path.exists(input_file):
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raise FileNotFoundError(f"Input file not found: {input_file}")
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if not output_file:
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output_file = input_file
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initial_size = os.path.getsize(input_file)
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gs = find_ghostscript_executable()
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if not gs:
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raise RuntimeError(
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"Ghostscript not found. Install it and ensure 'gs' (Linux/macOS) "
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"or 'gswin64c'/'gswin32c' (Windows) is in PATH."
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)
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settings_map = {
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0: '/screen',
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1: '/ebook',
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2: '/printer',
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3: '/prepress',
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4: '/default',
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}
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pdfsettings = settings_map.get(power, '/printer')
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cmd = [
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gs,
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'-sDEVICE=pdfwrite',
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'-dCompatibilityLevel=1.4',
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f'-dPDFSETTINGS={pdfsettings}',
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'-dNOPAUSE',
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'-dBATCH',
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'-dQUIET',
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f'-sOutputFile={output_file}',
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input_file,
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]
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try:
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subprocess.run(cmd, check=True)
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except subprocess.CalledProcessError as e:
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print(f"Ghostscript failed: {e}")
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return False
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compressed_size = os.path.getsize(output_file)
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ratio = 1 - (compressed_size / initial_size)
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summary = {
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"Input File": input_file,
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"Initial Size": get_size_format(initial_size),
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"Output File": output_file,
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"Compressed Size": get_size_format(compressed_size),
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"Compression Ratio": f"{ratio:.3%}",
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}
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print("## Summary ########################################################")
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for k, v in summary.items():
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print(f"{k}: {v}")
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print("###################################################################")
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return True
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if __name__ == '__main__':
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if len(sys.argv) < 3:
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print("Usage: python pdf_compressor_ghostscript.py <input.pdf> <output.pdf> [power 0-4]")
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sys.exit(1)
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input_file = sys.argv[1]
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output_file = sys.argv[2]
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power = int(sys.argv[3]) if len(sys.argv) > 3 else 2
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ok = compress_file(input_file, output_file, power)
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sys.exit(0 if ok else 2)
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PDFNetPython3==8.1.0
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# No Python dependencies required for Ghostscript-based compressor.
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# System dependency: Ghostscript
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# - macOS: brew install ghostscript
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# - Debian: sudo apt-get install -y ghostscript
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# - Windows: https://ghostscript.com/releases/
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#
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# The legacy script (pdf_compressor.py) depends on PDFNet (commercial) and a license key.

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