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Image MIME Reference
CMU-Raster

CMU Window Manager Raster

image/x-cmu-raster
VS

JPEG 2000 Image (HEIF Container)

image/hej2k
HEJ2K

A complete technical comparison of CMU Window Manager Raster and JPEG 2000 Image (HEIF Container) — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

Equal browser support

Feature Support

Feature CMU-Raster HEJ2K
Transparency (Alpha) ✕ No Yes
Animation Support ✕ No ✕ No
Progressive Loading ✕ No Yes
HDR Support ✕ No Yes
EXIF Metadata ✕ No Yes
ICC Color Profile ✕ No Yes
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 →
JPEG 2000 Image (HEIF Container)
image/hej2k
Extension
.hej2
Container HEIF / ISOBMFF (ISO/IEC 15444-16)
Compression Lossy / Lossless
Algorithm
JPEG 2000HTJ2K
Color Depth 8-bit, 10-bit, 12-bit, 16-bit
Developed by ISO/IEC JTC 1 / ITU-T
Released 2019
Magic Bytes
XX XX XX XX 66 74 79 70 6A 32 6B 69
Full HEJ2K reference →

Browser Support Comparison

Browser CMU-Raster HEJ2K
Chrome Chrome
✕ ✕
Firefox Firefox
✕ ✕
Safari Safari
✕ ✕
Edge Edge
✕ ✕
IE IE (Legacy)
✕ ✕
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
HEJ2K

HEJ2K Strengths

  • Brings the extensive capabilities of the HEIF container (like EXIF/XMP, thumbnails, and depth maps) to JPEG 2000
  • Supports mathematically lossless compression via wavelet transformation
  • High scalability and progressive decoding out of the box
Limitations
  • Extremely limited software support outside of niche industries
  • Zero native compatibility with web browsers
  • High computational complexity compared to simpler formats like JPEG or PNG

When to choose which format

CMU-Raster
Use CMU-Raster when…
  • Historical UNIX / Andrew Project Archival
  • Legacy Academic Computing Research
HEJ2K
Use HEJ2K when…
  • Medical Imaging
  • Geospatial Data
  • Scientific Archiving

More comparisons

CMU-Raster vs ACES → HEJ2K vs ACES → CMU-Raster vs APNG → HEJ2K vs APNG → CMU-Raster vs AVCI → HEJ2K vs AVCI → CMU-Raster vs AVCS → HEJ2K vs AVCS → CMU-Raster vs AVIF → HEJ2K vs AVIF → All comparisons →
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