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Image MIME Reference
AVIF

AV1 Image File Format

image/avif
VS

CMU Window Manager Raster

image/x-cmu-raster
CMU-Raster

A complete technical comparison of AV1 Image File Format and CMU Window Manager Raster — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

AVIF wins on browser support

Feature Support

Feature AVIF CMU-Raster
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
AV1 Image File Format
image/avif
Extension
.avif
Container HEIF / ISOBMFF
Compression AV1 Lossy / AV1 Lossless
Algorithm
AV1
Color Depth 8-bit, 10-bit, 12-bit
Developed by Alliance for Open Media (AOMedia)
Released 2019
Magic Bytes
XX XX XX XX 66 74 79 70 61 76 69 66
Full AVIF reference →
CMU Window Manager Raster
image/x-cmu-raster
Extension
.ras
Container CMU Window Manager Bitmap
Compression Uncompressed
Algorithm
None
Color Depth 1-bit (Monochrome), 8-bit (Indexed/Grayscale)
Developed by Carnegie Mellon University (CMU)
Released 1980s
Magic Bytes
F1 00 40 BB
Full CMU-Raster reference →

Browser Support Comparison

Browser AVIF CMU-Raster
Chrome Chrome
✓ 85+
 ✕
Firefox Firefox
✓ 93+
 ✕
Safari Safari
✓ 16+
 ✕
Edge Edge
✓ 121+
 ✕
IE IE (Legacy)
✕ ✕
AVIF

AVIF Strengths

  • Best-in-class compression — typically 20–50% smaller than WebP at equivalent quality
  • Native HDR and wide color gamut (BT.2020) support
  • Supports 8, 10, and 12-bit color depth
Limitations
  • Encoding is highly CPU-intensive — significantly slower than JPEG or WebP
  • Requires Edge 121+ (not supported in earlier Edge versions)
  • Limited support in native desktop image viewers
CMU-Raster

CMU-Raster Strengths

  • Incredibly simple, uncompressed binary structure that was easy for early, memory-constrained UNIX workstations to parse and render
Limitations
  • Completely obsolete and unsupported outside of niche historical command-line tools like Netpbm
  • The shared '.ras' file extension causes frequent file misidentification and system conflicts
  • Lacks all modern imaging features, including metadata, compression, and alpha channel transparency

When to choose which format

AVIF
Use AVIF when…
  • Next-Gen Websites
  • HDR Photography
  • High-Quality Web Images
CMU-Raster
Use CMU-Raster when…
  • Historical UNIX / Andrew Project Archival
  • Legacy Academic Computing Research

More comparisons

AVIF vs ACES → CMU-Raster vs ACES → AVIF vs APNG → CMU-Raster vs APNG → AVIF vs AVCI → CMU-Raster vs AVCI → AVIF vs AVCS → CMU-Raster vs AVCS → All comparisons →
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