[Tool Summary] img2pdf: Lossless Image-to-PDF Conversion Utility

img2pdf is one of the fastest and most efficient tools for converting images to PDF in a Linux environment. It's optimized for merging multiple images into a single PDF document or converting a single image, and it's Python-based.

In this post, I'd like to introduce a tool I occasionally use and consistently find myself thinking, "This is truly excellent." Its overwhelming speed, Linux-native lightness, and seamless integration with pipes make it a favorite.

Visualizing the image to PDF conversion process

1. Working Principle

Its most significant feature is 'No Re-encoding' during the merge process. * Traditional Methods (e.g., ImageMagick): These methods read image files, analyze pixel data, and then recompress them (lossily) to fit the PDF format. This process can be CPU-intensive and may lead to a reduction in image quality. * img2pdf Method: It directly embeds the binary data of the image files as-is (Lossless) into the PDF container. * Advantages: Offers overwhelmingly fast conversion speeds, preserves 100% of the original image quality, and results in efficient file sizes.

2. Installation & Removal

Installation (Ubuntu/Debian based)

sudo apt update
sudo apt install img2pdf

Removal

# Remove only the program
sudo apt remove img2pdf

# Remove configuration files and dependencies cleanly
sudo apt purge img2pdf
sudo apt autoremove

3. Usage Guide

Basic Merging

Use this to combine all PNG files in the current directory into a single PDF.

img2pdf *.png -o output.pdf

Merging in a Specific Order

You can specify the order by listing filenames directly.

img2pdf image1.png image2.png image3.png -o output.pdf

Setting Page Size and Margins (Advanced)

This is useful when you want to fit images to a specific standard (e.g., A4) or add margins.

# Fit image size to A4 and add 2cm border
img2pdf --pagesize A4 --border 2cm *.png -o output.pdf

Specifying a Custom Resolution (DPI)

Use this when you want to force a specific output resolution for your images.

img2pdf --dpi 300 *.png -o output.pdf

4. Developer's Note

  • Sorting Issue: The wildcard (*) in the Linux terminal recognizes numbers as strings.
    • Example: Files might be merged in the order of 1.png, 10.png, 2.png.
    • Solution: The safest approach is to save filenames with consistent padding, such as 01.png, 02.png ... 10.png.
  • Leveraging Pipes: It goes without saying that pipe utilization is one of Linux's most convenient features. You can take the output of other commands and instantly create a PDF.
find . -name "*.png" | sort | xargs img2pdf -o output.pdf

One-line Summary: "The best tool for creating PDFs without quality loss, at maximum speed, in a truly Linux-native way."