View GROUP4s

View any image in your browser. Filesizes up to 2.5GB. For free, forever.

All local

Our converter runs in your browser, so we never see your data.

Blazing fast

No uploading your files to a server—conversions start instantly.

Secure by default

Unlike other converters, your files are never uploaded to us.

What is the GROUP4 format?

Raw CCITT Group4

The GROUP4 image format, formally known as the CCITT (International Telegraph and Telephone Consultative Committee) Group 4 fax encoding, is a method used for compressing monochrome images. It was developed primarily for fax transmission, optimizing the storage and sharing of document images over telecommunication lines. Unlike its predecessors in the CCITT Group series, Group 4 offers superior compression efficiency, making it an ideal choice for high-resolution textual and line art images, which are common in document scanning and fax applications.

To understand the significance of the GROUP4 format, it's essential to delve into its technical aspects and operational mechanisms. GROUP4 is a type of lossless compression, which means it reduces file size without sacrificing any detail from the original image. This trait is crucial for documents where precision, such as exact reproduction of text and drawings, is vital. The compression method employed by GROUP4 is a two-dimensional coding scheme, which contrasts with the one-dimensional scheme used by its immediate predecessor, Group 3.

The basic principle behind GROUP4's efficiency is its use of Modified READ (Relative Element Address Designate) codes to compress data. This approach involves analyzing two lines of an image at a time, distinguishing between them to find patterns or repetitions. The algorithm encodes differences rather than the absolute values of each pixel, enabling more substantial compression by taking advantage of the repetitive nature of document images. For instance, a large white space, which is common in documents, can be encoded in just a few bits.

GROUP4 compression utilizes a combination of Run Length Encoding (RLE) and Huffman coding. RLE is a simple form of data compression where sequences of the same data value (in this case, pixel color - black or white) are stored as a single data value and count. Huffman coding is a more complex method that assigns shorter codes to more frequent values. In the context of GROUP4, Huffman coding optimizes the encoding of run lengths, thereby enhancing the overall compression ratio.

Another distinguishing feature of the GROUP4 format is its ability to perform end-of-block (EOB) sequences, allowing for the efficient encoding of large areas of uniform color. When the encoder detects a significant expanse of white or black pixels without variation, it generates an EOB code. This signal tells the decoder that the rest of the block (or line) consists of pixels of the same color, effectively compressing vast areas with minimal data. This feature significantly contributes to the high compression ratios achievable with GROUP4, especially in documents with large margins or spacing.

The encoding process in GROUP4 compression begins with the scanning of the image in a raster fashion, line by line. The algorithm compares each current line with the one before it, determining the differences and encoding them based on predefined rules. These rules are designed to capture and encode the variety of patterns that can occur between two lines, such as changes from white to black (transitions) and prolonged sequences of a single color. The encoding process effectively compresses the information by reducing redundancy, which is a hallmark of document images.

One of the unique advantages of the GROUP4 format is its scalability and adaptability across various resolutions and sizes. This flexibility makes it highly suitable for a wide range of document imaging applications, from small-scale business fax transmissions to large archival systems. Furthermore, the lossless nature of the compression ensures that the quality of the scanned image remains intact, no matter the level of compression. This feature is critically important for legal, medical, and archival documents where fidelity to the original is paramount.

Despite its numerous advantages, the GROUP4 format has some limitations. One major limitation is its restriction to monochrome (black and white) images. While this is not a downside for document imaging and faxing purposes, it does limit the utility of GROUP4 for applications requiring color or gray scale, such as photography or detailed maps. Additionally, because GROUP4 compression is designed to exploit the redundancy typical of documents, it may not perform as well on images that lack clear patterns or large uniform areas.

The implementation and adoption of GROUP4 compression have been widespread in the document imaging and communication industry, thanks to its efficiency and the cost-saving benefits it offers. Many document scanners and fax machines support GROUP4 as a standard, making it a ubiquitous format in offices and government institutions worldwide. Additionally, the TIFF (Tagged Image File Format) standard, a popular format for storing high-quality images, includes support for GROUP4 compression, further cementing its role in document management systems.

Software-wise, several document management, and scanning applications provide support for the GROUP4 format, allowing users to select it as a preferred method for storing scanned documents. This software support extends the utility of GROUP4 beyond hardware implementations, making it accessible for digital archiving, email attachments, and web publishing. The format's efficient compression capabilities mean that high-resolution document images can be shared and stored conveniently without significant storage or bandwidth demands.

Technological advancements continue to shape the landscape of document imaging and communication, with newer formats and compression methods emerging. However, the GROUP4 format maintains its relevance due to its unmatched efficiency in compressing monochrome document images and its widespread support across devices and software. As organizations and industries continue to prioritize cost-effective and reliable document handling solutions, GROUP4 remains a valuable asset in the digital document management toolkit.

In conclusion, the CCITT Group 4 fax encoding standard represents a significant development in the field of document image compression. Its sophisticated use of two-dimensional coding, combined with advanced techniques such as Modified READ codes, Run Length Encoding, and Huffman coding, enables the efficient reduction of file sizes while retaining image quality. Despite some limitations, such as its applicability solely to monochrome images, GROUP4's flexibility, compression efficiency, and broad support make it an enduring choice for document imaging and fax transmission applications. The GROUP4 format's role in facilitating the digital storage and transmission of document images underscores its importance in modern communication and information management systems.

Supported formats

AAI.aai

AAI Dune image

AI.ai

Adobe Illustrator CS2

AVIF.avif

AV1 Image File Format

AVS.avs

AVS X image

BAYER.bayer

Raw Bayer Image

BMP.bmp

Microsoft Windows bitmap image

CIN.cin

Cineon Image File

CLIP.clip

Image Clip Mask

CMYK.cmyk

Raw cyan, magenta, yellow, and black samples

CMYKA.cmyka

Raw cyan, magenta, yellow, black, and alpha samples

CUR.cur

Microsoft icon

DCX.dcx

ZSoft IBM PC multi-page Paintbrush

DDS.dds

Microsoft DirectDraw Surface

DPX.dpx

SMTPE 268M-2003 (DPX 2.0) image

DXT1.dxt1

Microsoft DirectDraw Surface

EPDF.epdf

Encapsulated Portable Document Format

EPI.epi

Adobe Encapsulated PostScript Interchange format

EPS.eps

Adobe Encapsulated PostScript

EPSF.epsf

Adobe Encapsulated PostScript

EPSI.epsi

Adobe Encapsulated PostScript Interchange format

EPT.ept

Encapsulated PostScript with TIFF preview

EPT2.ept2

Encapsulated PostScript Level II with TIFF preview

EXR.exr

High dynamic-range (HDR) image

FARBFELD.ff

Farbfeld

FF.ff

Farbfeld

FITS.fits

Flexible Image Transport System

GIF.gif

CompuServe graphics interchange format

GIF87.gif87

CompuServe graphics interchange format (version 87a)

GROUP4.group4

Raw CCITT Group4

HDR.hdr

High Dynamic Range image

HRZ.hrz

Slow Scan TeleVision

ICO.ico

Microsoft icon

ICON.icon

Microsoft icon

IPL.ipl

IP2 Location Image

J2C.j2c

JPEG-2000 codestream

J2K.j2k

JPEG-2000 codestream

JNG.jng

JPEG Network Graphics

JP2.jp2

JPEG-2000 File Format Syntax

JPC.jpc

JPEG-2000 codestream

JPE.jpe

Joint Photographic Experts Group JFIF format

JPEG.jpeg

Joint Photographic Experts Group JFIF format

JPG.jpg

Joint Photographic Experts Group JFIF format

JPM.jpm

JPEG-2000 File Format Syntax

JPS.jps

Joint Photographic Experts Group JPS format

JPT.jpt

JPEG-2000 File Format Syntax

JXL.jxl

JPEG XL image

MAP.map

Multi-resolution Seamless Image Database (MrSID)

MAT.mat

MATLAB level 5 image format

PAL.pal

Palm pixmap

PALM.palm

Palm pixmap

PAM.pam

Common 2-dimensional bitmap format

PBM.pbm

Portable bitmap format (black and white)

PCD.pcd

Photo CD

PCDS.pcds

Photo CD

PCT.pct

Apple Macintosh QuickDraw/PICT

PCX.pcx

ZSoft IBM PC Paintbrush

PDB.pdb

Palm Database ImageViewer Format

PDF.pdf

Portable Document Format

PDFA.pdfa

Portable Document Archive Format

PFM.pfm

Portable float format

PGM.pgm

Portable graymap format (gray scale)

PGX.pgx

JPEG 2000 uncompressed format

PICON.picon

Personal Icon

PICT.pict

Apple Macintosh QuickDraw/PICT

PJPEG.pjpeg

Joint Photographic Experts Group JFIF format

PNG.png

Portable Network Graphics

PNG00.png00

PNG inheriting bit-depth, color-type from original image

PNG24.png24

Opaque or binary transparent 24-bit RGB (zlib 1.2.11)

PNG32.png32

Opaque or binary transparent 32-bit RGBA

PNG48.png48

Opaque or binary transparent 48-bit RGB

PNG64.png64

Opaque or binary transparent 64-bit RGBA

PNG8.png8

Opaque or binary transparent 8-bit indexed

PNM.pnm

Portable anymap

PPM.ppm

Portable pixmap format (color)

PS.ps

Adobe PostScript file

PSB.psb

Adobe Large Document Format

PSD.psd

Adobe Photoshop bitmap

RGB.rgb

Raw red, green, and blue samples

RGBA.rgba

Raw red, green, blue, and alpha samples

RGBO.rgbo

Raw red, green, blue, and opacity samples

SIX.six

DEC SIXEL Graphics Format

SUN.sun

Sun Rasterfile

SVG.svg

Scalable Vector Graphics

SVGZ.svgz

Compressed Scalable Vector Graphics

TIFF.tiff

Tagged Image File Format

VDA.vda

Truevision Targa image

VIPS.vips

VIPS image

WBMP.wbmp

Wireless Bitmap (level 0) image

WEBP.webp

WebP Image Format

YUV.yuv

CCIR 601 4:1:1 or 4:2:2

Frequently asked questions

How does this work?

This converter runs entirely in your browser. When you select a file, it is read into memory and converted to the selected format. You can then download the converted file.

How long does it take to convert a file?

Conversions start instantly, and most files are converted in under a second. Larger files may take longer.

What happens to my files?

Your files are never uploaded to our servers. They are converted in your browser, and the converted file is then downloaded. We never see your files.

What file types can I convert?

We support converting between all image formats, including JPEG, PNG, GIF, WebP, SVG, BMP, TIFF, and more.

How much does this cost?

This converter is completely free, and will always be free. Because it runs in your browser, we don't have to pay for servers, so we don't need to charge you.

Can I convert multiple files at once?

Yes! You can convert as many files as you want at once. Just select multiple files when you add them.