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Image MIME Reference
Compressed-XCF

Compressed GIMP XCF Image

image/x-compressed-xcf
VS

RealNetworks RealPix

image/vnd.rn-realpix
RealPix

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

Equal browser support

Feature Support

Feature Compressed-XCF RealPix
Transparency (Alpha) Yes Yes
Animation Support Yes Yes
Progressive Loading ✕ No Yes
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 →
RealNetworks RealPix
image/vnd.rn-realpix
Extension
.rp
Container IMFL (XML Markup)
Compression Uncompressed (Plain Text Markup)
Algorithm
None (Plain Text)
Color Depth Dependent on referenced images
Developed by RealNetworks
Released 1998
Magic Bytes
3C 69 6D 66 6C
Full RealPix reference →

Browser Support Comparison

Browser Compressed-XCF RealPix
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
RealPix

RealPix Strengths

  • Allowed for 'Ken Burns'-style animated slideshows at a fraction of the bandwidth required for actual video, crucial for 1990s dial-up connections
  • Plain text XML architecture made it easy for developers and hobbyists to hand-code complex multimedia presentations
  • Perfectly synchronized with RealAudio streams using SMIL-like timing parameters
Limitations
  • Completely obsolete and heavily reliant on the proprietary, defunct RealPlayer browser plugin
  • Not a true image format, causing confusion when handled by standard image processing libraries which expect binary pixel data
  • Lacks modern CSS or HTML5 canvas equivalents without completely rewriting the presentation logic

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
RealPix
Use RealPix when…
  • Historical Dial-up Streaming Presentations
  • RealPlayer Slideshows
  • Bandwidth-efficient 'Video' Alternatives (late 1990s)

More comparisons

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