Scanned File Types Explained: TIFF, JPEG, PDF, PDF/A and Compression

In this article

1. Two ideas to understand first
2. The common file types
3. What is the difference between PDF and PDF/A?
4. Which compression should I use?
5. What are master and access copies?
6. Choosing a format by purpose
7. What Australian archives recommend
8. Common pitfalls
9. Frequently asked questions
10. Where to start

The file type you scan to affects how big the files are, how long they stay readable, how easily they can be shared and how much detail is kept. Choosing it after scanning has started usually means rescanning, so decide first.

This guide explains the common file types and what compression means, and shows what Australian archives recommend. It is general information, not legal advice. Requirements differ by organisation and type of record, so check which rules apply to you.

Two ideas to understand first

An image format and a document format are different things. A scanner produces a picture of each page. An image format, such as TIFF or JPEG, stores that picture. A document format, such as PDF, is a container that can hold one or many page images, and can also hold searchable text.

Compression makes files smaller. Without it, a large scan can be tens or hundreds of megabytes. There are two kinds:

• Lossless compression shrinks the file and can restore every detail exactly, like zipping a document.
• Lossy compression shrinks the file further by permanently throwing away detail the eye is least likely to miss. The loss cannot be undone, and it builds up if the file is saved again.

Most choices come down to these two ideas: what the file is for, and how much detail you can afford to lose.

The common file types

No single format is best for everything. Most organisations use one format for the master copy they keep, and another for the copies people use every day.

What is the difference between PDF and PDF/A?

"PDF" covers several different things, and the differences matter.

• Image-only PDF. Each page is a picture. It looks right, but you cannot search or copy the words.
• Searchable PDF. The page picture is kept, and a layer of recognised text (from OCR) sits behind it. You see the original page and can search it. This is the usual choice for scanned documents.
• PDF/A. A version of PDF designed for long-term keeping. Fonts are embedded, and the file cannot depend on outside resources or rely on features that may stop working, such as encryption or scripts. The aim is that it looks the same in many years' time.

PDF/A is an international standard (ISO 19005) published in parts:

Parts 1 to 3 also have conformance levels, shown as a letter after the number:

• b (basic) makes sure the page looks the same in future.
• u (Unicode) also makes sure the text can be reliably searched and copied. It applies to parts 2 and 3.
• a (accessible) goes further and keeps the page structure, so screen readers can read it.

For scanned records, PDF/A-2b is a common choice, and PDF/A-2u when a searchable text layer is included. A file is only PDF/A if it passes a validation check, not because it carries the label, so confirm it with a checking tool, particularly if records must meet a standard.

Which compression should I use?

Compression is a trade-off between file size and the detail you keep. As a rough guide, one A4 page at 300 dpi gives these sizes (estimates, since it varies by page):

Uncompressed is the safest and the largest. It suits master copies where storage is not the limit.

Lossless compression keeps every detail and reduces size. For colour and greyscale, this means methods such as LZW and ZIP inside a TIFF, or lossless PNG. For black and white pages, a method designed for black and white gives very small files. It suits master copies and records you may need to look at closely.

Lossy compression gives the smallest files and suits viewing copies and photographs. It is less suited to text and line drawings, where it can blur edges and leave marks around letters. Set the quality high, and do not repeatedly open, edit and resave the same lossy file, because the loss builds up. For black and white text, avoid very aggressive compression settings, which in rare cases can alter characters.

A simple rule: use lossless or none for what you keep, and lossy only for convenience copies, and only when the loss does not matter for the purpose.

What are master and access copies?

Many organisations keep two versions of every scan.

• The master copy is the best-quality version, kept as the reference. It is not used day to day. It is stored safely and used to make other copies when needed.
• The access copy is a smaller version for everyday viewing, sharing and emailing. If it is lost or damaged, you make another from the master.

Quality cannot be added later. You can always make a smaller copy from a high-quality master, but you cannot recover detail that was never captured, or that was discarded by compression. Capturing once at a good standard avoids the cost of rescanning.

The cost is storage, because you keep both. Even so, the access copies are usually small, so the master copy decides how much space you need.

Choosing a format by purpose

If you are unsure, a TIFF master plus a searchable PDF for use is a safe and common combination.

What Australian archives recommend

National and state archives publish digitisation guidance. It is written for government bodies, but it is a useful reference for anyone choosing a format, and it agrees on more than it differs. Use this as a guide only and check the current version for your records, because guidance is updated from time to time.

For South Australia, contact State Records of South Australia for the guidance that applies to your records.

A few themes appear across most of them:

• TIFF is the usual choice for the master copy, with PDF/A and JPEG 2000 accepted in some guidance.
• Keep the master lossless or uncompressed. Lossy compression is for access copies.
• Keep a master and a smaller access copy, rather than one file that does both jobs.
• Resolution is part of the standard, and it cannot be raised after scanning.
• Different records, different rules. Records of permanent value are held to a higher standard than routine ones.

They do not agree on everything. Tasmania keeps preservation TIFFs uncompressed, while Western Australia and the National Archives also allow lossless compression. The Northern Territory defaults to a searchable PDF at 300 dpi, and Queensland does not prescribe a format. Resolution minimums range from 300 ppi to 600 ppi depending on the record.

Common pitfalls

• Choosing the format after scanning starts. Changing later often means rescanning.
• Saving only a compressed copy. Detail that has been thrown away cannot be restored.
• Resaving a lossy file. Each save can lower the quality further.
• Assuming every PDF is PDF/A. Only files that pass a check meet the standard.
• Image-only PDFs. Pages that look fine but cannot be searched are hard to use at scale.
• Forgetting file size. A colour master of every page adds up quickly, so estimate the storage first.
• Using the same file for everything. A master that is too big to share, or a viewing copy that is too poor to keep, causes problems either way.
• Ignoring the rules that apply. Some records must meet a named standard, so check before you decide.

Frequently asked questions

What is the difference between PDF and PDF/A?

PDF/A is a restricted form of PDF made for long-term keeping. It embeds fonts and avoids features that may stop working, so the file looks the same in future. A file is only PDF/A if it passes a validation check.

Is TIFF better than PDF?

They do different jobs. TIFF is an image format often used for master copies because it keeps full quality. PDF is a document format that is easier to share and can hold searchable text.

What is a searchable PDF?

A PDF that keeps the picture of each page and adds a hidden layer of recognised text behind it, so you can search and copy the words.

Should I use lossless or lossy compression?

Use lossless or no compression for what you keep, and lossy only for convenience copies where losing some detail does not matter.

What is a master copy?

The best-quality version of a scan, kept as the reference and used to make smaller access copies when needed.

Where to start

A good first step is to decide four things: what the scans are for, how long they must be kept, which rules apply to your records, and how people will use them day to day. The answers usually point to a master format and an access format.

Vision and Beyond helps organisations choose scanners and capture settings, set up indexing and searchable files, and manage records. We stay involved after the equipment is installed. If you would like to talk through the right file types for your records, send us a message with the kinds of documents you scan and what you need to do with them.

These guides may also help:

• How to Choose the Right Scanner
• Digitising Paper Archives: Where to Start
• Digitising Drawings, Plans and Maps
• Keeping Records Compliant: Retention, Disposal and Audit Trails