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Image MIME Reference
Compressed-XCF

Compressed GIMP XCF Image

image/x-compressed-xcf
VS

Group 3 Fax Image

image/g3fax
G3-Fax

A complete technical comparison of Compressed GIMP XCF Image and Group 3 Fax Image — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

Equal browser support

Feature Support

Feature Compressed-XCF G3-Fax
Transparency (Alpha) Yes ✕ No
Animation Support Yes ✕ No
Progressive Loading ✕ No ✕ No
HDR Support Yes ✕ No
EXIF Metadata Yes ✕ No
ICC Color Profile Yes ✕ No
Compressed GIMP XCF Image
image/x-compressed-xcf
Extension
.xcf.gz.xcf.bz2.xcfgz.xcfbz2
Container Gzip or Bzip2 Archive
Compression Gzip (Deflate) / Bzip2
Algorithm
DeflateBWT (Burrows-Wheeler)
Color Depth 8-bit (Per Channel), 16-bit (Integer/Floating Point), 32-bit (Integer/Floating Point)
Developed by The GIMP Team
Released 1995
Magic Bytes
1F 8B 08 (gzip) or 42 5A 68 (bzip2)
Full Compressed-XCF reference →
Group 3 Fax Image
image/g3fax
Extension
.g3
Container Raw Bitstream
Compression Lossless (CCITT Group 3)
Algorithm
CCITT Group 3 (Modified Huffman / READ)
Color Depth 1-bit (Monochrome)
Developed by CCITT (now ITU-T) / IETF
Released 1980
Magic Bytes
None (Raw Bitstream)
Full G3-Fax reference →

Browser Support Comparison

Browser Compressed-XCF G3-Fax
Chrome Chrome
✕ ✕
Firefox Firefox
✕ ✕
Safari Safari
✕ ✕
Edge Edge
✕ ✕
IE IE (Legacy)
✕ ✕
Compressed-XCF

Compressed-XCF Strengths

  • Drastically reduces the massive file sizes of standard XCF project files, saving significant disk space
  • Preserves 100% of the non-destructive editing data (layers, masks, paths, guides) from the GIMP workspace
  • Uses standard, universally supported compression algorithms (gzip/bzip2) meaning the archive can be rescued or extracted by standard OS tools if GIMP is unavailable
Limitations
  • Increases file load and save times due to the CPU overhead required to compress and decompress the massive pixel arrays
  • Impossible for automated tools to parse metadata or dimensions without first unarchiving the payload into memory
  • File extension combinations (.xcf.gz) can confuse basic MIME sniffers which stop reading at the .gz extension
G3-Fax

G3-Fax Strengths

  • Extremely efficient compression for 1-bit black-and-white text and line art
  • Standardized via RFC 1494 for email and internet fax transmission
  • Low bandwidth requirements
Limitations
  • Raw format lacks metadata (such as image width and resolution), requiring out-of-band information to decode accurately
  • Strictly limited to 1-bit monochrome imagery
  • Zero native web browser support

When to choose which format

Compressed-XCF
Use Compressed-XCF when…
  • GIMP Multi-layer Project Archival
  • Saving disk space for complex raster edits
  • Open-source graphic design workflows
G3-Fax
Use G3-Fax when…
  • Telefacsimile (Fax) Transmission
  • Internet Fax (T.37)
  • Document Archiving
  • Telephony Systems

More comparisons

Compressed-XCF vs ACES → G3-Fax vs ACES → Compressed-XCF vs APNG → G3-Fax vs APNG → Compressed-XCF vs AVCI → G3-Fax vs AVCI → Compressed-XCF vs AVCS → G3-Fax vs AVCS → Compressed-XCF vs AVIF → G3-Fax vs AVIF → All comparisons →
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