Creating PDFs from multiple images on Linux

Hey there! Today, I want to share a nifty little trick that I recently discovered and help me a lot – how to merge a bunch of images into a single PDF file using the Linux command line. So, let's dive right into it!

The Command: convert (from the ImageMagick Package)

The magic tool that we're going to use here is convert, which is a part of the ImageMagick package – a powerful suite of command-line tools for image manipulation. If you don't have it installed, you can usually install it using your package manager. For instance, on Debian-based systems, you'd run:

sudo apt-get install imagemagick

Configuring ImageMagick Policies for PDF Writing

ImageMagick's security policies are designed to ensure that image and file operations are performed in a safe and secure manner, preventing potential abuses. This means that certain features, such as writing PDF files, might be disabled by default for security reasons.

It PDF writing is disable you may encounter this error:

attempt to perform an operation not allowed by the security policy 'PDF' @ error/constitute.c/IsCoderAuthorized/421

To enable writing PDF files using the convert command, you'll need to modify ImageMagick's security policies. Here's how to do it:

1. Locate the policy file: ImageMagick's policy files are usually located in the /etc/ImageMagick-<version>/ directory. The file name is policy.xml.

2. Edit the policy file: Open the policy.xml file with a text editor as an administrator (use sudo for administrative rights).

3. Find the <policymap> section: Inside the policy.xml file, you'll find a <policymap> section. This is where you'll define policies for each file format.

4. Enable PDF writing: To enable writing PDF files, locate the line that corresponds to the PDF pattern. Modify the value of rights to allow PDF writing. For example:

<policy domain="coder" rights="read | write" pattern="PDF" />

The Command Syntax

The basic syntax of the convert command for merging images into a PDF is as follows:

convert image1.jpg image2.png output.pdf

You simply list the input images in the order you want them to appear in the PDF, followed by the desired output PDF file name.

Combining Multiple Images

But what if you have a bunch of images in a folder that you want to merge in a specific order? No worries, we can use shell globbing to our advantage. Here's how:

convert *.jpg output.pdf

This command would merge all the JPEG images in the current folder into a single PDF named output.pdf.