Utility for converting a directory of images to a PDF

Converting a directory of images into a single PDF is efficiently handled by the img2pdf utility, which preserves original image quality without re-encoding. Unlike tools that compress or alter pixels, this tool performs a lossless merge, making it ideal for archival purposes or high-fidelity document preparation where visual integrity is paramount.

Why Choose img2pdf Over Other Tools?

Many users default to command-line tools like ImageMagick or graphical interfaces for merging images. However, these methods often involve rasterizing the images again, which can introduce compression artifacts and increase file size unnecessarily. The primary advantage of using img2pdf is that it does not decode and re-encode the image data. Instead, it simply places the existing JPEG or PNG streams directly into the PDF container. This process ensures that the output PDF is bit-for-bit identical in terms of pixel data to the source images, just organized within a page structure. This approach is particularly useful when you need to maintain the highest possible resolution for printing or professional documentation. If you are working with a large batch of photos, avoiding re-encoding saves significant processing time and storage space. For more complex PDF manipulations, such as extracting content from existing files, you might also find our guide on How to Unarchive, Extract, Unpack, and Disassemble PDF Files helpful for understanding the underlying structure of PDF documents.

Installation and Setup

Before converting your images, you must install the utility. Because img2pdf is a Python-based tool, it is most easily installed via pip, the Python package installer. Open your terminal or command prompt and run the following command:

pip install img2pdf

If you are using a Linux distribution with a package manager, you may also find it available through repositories like Ubuntu's APT or Fedora's DNF. On macOS, Homebrew users can install it via brew install img2pdf. Once installed, verify the installation by checking the version number:

img2pdf --version

This step confirms that the binary is accessible from your system path, allowing you to execute conversion commands directly from any directory.

Basic Conversion Workflow

The most common use case involves converting all images in a specific folder into a single PDF. Navigate to the directory containing your images using the cd command. Then, use a glob pattern to select all relevant image files. The basic syntax is straightforward:

img2pdf *.jpg -o output.pdf

In this command, *.jpg selects all JPEG files in the current directory. You can replace this with *.png for PNG files or combine extensions like *.jpg *.png if your folder contains mixed formats. The -o flag specifies the name of the output file. If you omit the -o flag, img2pdf will print the PDF data to standard output (stdout), which you can redirect to a file using shell redirection (> output.pdf). For more precise control over the order of pages, avoid using wildcards that rely on alphabetical sorting if your filenames do not reflect the desired sequence. Instead, list the files explicitly in the command line:

img2pdf photo1.jpg photo2.jpg photo3.jpg -o sequence.pdf

This ensures that the pages appear in the exact order you specify, which is crucial for photo albums or sequential diagrams.

Handling Mixed Formats and Subdirectories

If your images are spread across subdirectories, you can use the --glob option with recursive patterns or use a tool like find to generate the file list. For example:

find . -name "*.jpg" -print0 | xargs -0 img2pdf -o merged.pdf

This pipeline finds all JPEG files recursively and passes them to img2pdf. Be cautious with very large numbers of files, as command-line argument limits may apply. In such cases, splitting the operation into smaller batches or using a script is recommended.

Optimizing Page Layout and Orientation

By default, img2pdf creates one page per image. It automatically detects the orientation of each image and sets the page size to match the image dimensions. This means landscape images result in landscape pages, and portrait images result in portrait pages. This dynamic sizing is a key feature that distinguishes it from static converters. However, if you need uniform page sizes regardless of image orientation, you can enforce a specific paper size using the --pagesize option. For instance, to force all pages to A4 size:

img2pdf *.jpg --pagesize A4 -o fixed_size.pdf

Note that forcing a specific page size may add white margins around images that do not match the aspect ratio of the target paper size. If you want to center the image on the page rather than stretching it, you may need additional post-processing tools, as img2pdf focuses strictly on embedding the raw image data.

Advanced Options and Troubleshooting

Sometimes, you may encounter issues with certain image metadata or color profiles. img2pdf generally handles standard RGB and CMYK JPEGs well. If you experience errors related to unsupported formats, ensure your images are valid JPEGs or PNGs. Corrupted headers can cause the parser to fail. For transparency handling in PNGs, the tool converts alpha channels to a white background by default to ensure compatibility with older PDF viewers. If you need to preserve transparency, you may need to configure the output settings or use a different converter, though standard PDF viewers typically support alpha blending. If you are looking to convert HTML files to PDF instead, which is a different workflow involving rendering web content, you might prefer our article on Convert HTML Files to PDF for those specific use cases.

Frequently Asked Questions

Does img2pdf reduce the file size of my images?

No, it does not compress or resize the images. It embeds the original data streams, so the resulting PDF size will be roughly the sum of the image file sizes plus minimal PDF overhead. This ensures zero quality loss but results in larger files compared to compressed converters.

Can I convert TIFF images to PDF using this tool?

Standard img2pdf primarily supports JPEG and PNG formats. While some forks or updated versions may support TIFF, the core stable release focuses on web-friendly formats. For TIFF support, consider using ImageMagick or Ghostscript as alternative utilities.

How do I merge PDFs with images after conversion?

You can use other PDF manipulation tools like qpdf or pdftk to append the generated PDF to an existing document. Since img2pdf produces a standard PDF, it integrates seamlessly with other PDF libraries and command-line tools.

Is there a way to set custom DPI for the output pages?

img2pdf does not resample images, so DPI is largely irrelevant to the visual quality since the pixels remain unchanged. However, some PDF viewers use DPI information for zooming defaults. To influence this, you would need to modify the PDF metadata after creation, as the tool itself does not expose DPI adjustment flags.

What happens if I have non-image files in the directory?

The tool will ignore files that do not match the specified extension pattern (e.g., *.jpg). If you use a broad wildcard like *, it may attempt to parse non-image files, leading to errors. Always restrict the input to known image extensions to prevent parsing failures.