SK to G4 Converter

Free SK to G4 conversion — Group 4 fax compression

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Document Standard

Group 4 compression is the standard for digital fax and document scanning. Convert SK drawings to G4 for document archival workflows.

Fast and Compact

G4 produces highly compressed output. The conversion is quick, and the resulting files are very small in size.

Secure Process

SK uploads are deleted after conversion. G4 files are automatically purged from Convertio servers within 24 hours.

How to convert SK to G4

1

Select files from Computer, Google Drive, Dropbox, URL or by dragging it on the page.

2

Choose g4 or any other format you need as a result (more than 200 formats supported)

3

Let the file convert and you can download your g4 file right afterwards

About formats

SK is the native file format of Skencil (originally named Sketch), a free vector graphics editor for Linux created by Bernhard Herzog, with the first public release on October 31, 1998. Skencil holds historical significance as one of the earliest full-featured vector drawing applications written almost entirely in Python, with only performance-critical rendering components implemented in C. The SK file format uses a text-based, Python-like syntax to describe document structure — pages, layers, groups, and individual graphic objects are represented as nested statements with parameters specifying coordinates, colors, line styles, and transformations. The format supports Bezier curves, rectangles, ellipses, text objects with font specifications, imported raster images, gradient and pattern fills, and hierarchical grouping with affine transforms. One advantage is human readability — SK files can be opened in any text editor, making it possible to inspect, modify, or generate artwork programmatically using simple scripts. The Python-native structure also provides a benefit for automation: since Skencil itself is a Python application, the file format integrates naturally with scripting workflows for batch processing and procedural graphic generation. While Skencil's development slowed after the mid-2000s, its SK format became the foundation for the sK1 project, which extended the format and continued active open-source vector graphics development. SK files remain convertible through sK1, UniConvertor, and other open-source tools.
Developer: Bernhard Herzog
Initial release: October 31, 1998
G4 is a monochrome image format based on the ITU-T Group 4 facsimile coding standard (Recommendation T.6), ratified by the CCITT in 1984 as an improvement over Group 3 for use on error-free digital networks like ISDN rather than analog telephone lines. G4 files contain 1-bit image data compressed using exclusively two-dimensional Modified Modified READ (MMR) coding, where each scanline is encoded as a set of differences (changing elements) relative to the line above it. By eliminating the one-dimensional coding fallback and the end-of-line synchronization markers required by Group 3, G4 achieves 20-50% better compression ratios on typical document pages while producing a simpler, more regular bitstream. The format is most commonly encountered as a compression method within TIFF files (TIFF compression tag 4), where it became the standard archival format for scanned documents in enterprise document management, government records, and legal imaging systems. G4 compression is specified at 200, 300, or 400 dpi depending on the scanning application, with 300 dpi being the most common for archival-quality document imaging. One advantage is exceptional compression efficiency for document content: G4's two-dimensional prediction exploits the strong vertical correlation in text and line art pages, typically compressing a 300 dpi letter-size page to 30-50 KB — roughly half the size of equivalent Group 3 encoding. The format's entrenchment in document management infrastructure is another strength — G4 TIFF is the mandated format for many government digital records systems, court filing systems, and corporate archives, supported by every enterprise imaging platform.
Developer: ITU-T (CCITT)
Initial release: 1984

Frequently Asked Questions

Why convert SK to G4?

G4 uses ITU Group 4 compression — the standard for digital fax and scanned documents. SK to G4 creates compact monochrome images.

What software reads G4 files?

Fax systems, TIFF viewers (G4 often wraps in TIFF), IrfanView, and document scanning tools support Group 4 compressed images.

Is G4 better than G3?

G4 generally achieves higher compression ratios than G3 for the same image data, making it more storage-efficient.

Is the output monochrome?

Yes — Group 4 compression is designed for bi-level images. Your SK artwork is rendered as a black-and-white bitmap.

Is this conversion free?

Convertio offers free SK to G4 conversion. Premium accounts add higher limits and priority processing speeds.