Convert G4 Image Free

How to Convert Files

Convert G4 fax images to and from standard formats in your browser, with all processing done locally on your device.

What a G4 file holds

G4 holds a monochrome image compressed with CCITT Group 4, a more efficient successor to Group 3 fax encoding. Like Group 3 it stores a one-bit black-and-white image, but it compresses that data more tightly, which is why it became the common choice for archived document scans.

Group 4 uses two-dimensional coding: instead of describing each row independently, it encodes each line by referring to the line above it, exploiting the fact that adjacent rows of a document are usually similar. This vertical correlation lets it store the same page in less space than Group 3, while remaining lossless for the bilevel image.

Strengths and limits

Group 4 is the most compact of the standard fax encodings for text-like pages, lossless, and widely supported in document-imaging systems, which is why large scanned-document archives rely on it.

It shares Group 3's essential limit: it is one-bit monochrome only, unsuitable for greyscale or colour and optimised for documents rather than photographs. Continuous-tone or colour images need a different format such as TIFF with a suitable codec, or PNG.

History of G4 Format

The G4 format was developed by the CCITT in the early 1990s as part of a suite of standards for fax communication. It aimed to improve upon the existing Group 3 standard by providing more efficient compression for monochrome images. This was particularly important for reducing transmission times and storage requirements for faxed documents, which were prevalent in business and legal environments.

G4 was standardized as part of the ITU T.6 recommendation in 1993. Its adoption was driven by the increasing need for digital archiving of documents. Over time, G4 became widely supported in various document management systems, leading to its integration into scanning software and hardware. This widespread compatibility solidified G4's role as a de facto standard for lossless monochrome image storage.

Practical Use of G4

Choose G4 when working with high volumes of monochrome document scans, especially when storage space and transmission efficiency are priorities. It is ideal for text-heavy documents such as contracts, reports, and invoices. If a document will be archived or shared in a fax-oriented workflow, G4 is often the best choice due to its lossless compression and wide support across platforms.

When converting to or from G4, ensure that your software supports CCITT Group 4 compression. Some image formats, like JPEG, do not maintain the same fidelity for monochrome images. Be aware of potential compatibility issues with older systems that may only support Group 3. For optimal results, test conversions to confirm that text clarity and image integrity are preserved.

Working with G4 files

You will meet Group 4 compression most often inside multi-page TIFF files used for scanned document archives, where its tight compression keeps large collections manageable.

To view or edit a single page, convert it to PNG. To keep an archive compact while preserving multiple pages in one file, a multi-page TIFF with Group 4 compression remains an excellent choice.