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Image MIME Reference
CMU-Raster

CMU Window Manager Raster

image/x-cmu-raster
VS

PTI Image (Personal/Vanity Tree)

image/prs.pti
PTI

A complete technical comparison of CMU Window Manager Raster and PTI Image (Personal/Vanity Tree) — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

Equal browser support

Feature Support

Feature CMU-Raster PTI
Transparency (Alpha) ✕ No ✕ No
Animation Support ✕ No ✕ No
Progressive Loading ✕ No ✕ No
HDR Support ✕ No ✕ No
EXIF Metadata ✕ No ✕ No
ICC Color Profile ✕ No ✕ No
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 →
PTI Image (Personal/Vanity Tree)
image/prs.pti
Extension
.pti
Container Proprietary
Compression Unknown / Proprietary
Algorithm
Unknown
Color Depth Unknown
Developed by Jürn Laun
Released 1999
Magic Bytes
Unknown
Full PTI reference →

Browser Support Comparison

Browser CMU-Raster PTI
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
PTI

PTI Strengths

  • Provided a registered MIME type namespace for a specific application's proprietary image format without conflicting with standard web types
Limitations
  • Completely undocumented and unsupported in modern ecosystems
  • Zero web browser compatibility
  • Falls into the 'vanity' tree, making it irrelevant for standard cross-platform data exchange

When to choose which format

CMU-Raster
Use CMU-Raster when…
  • Historical UNIX / Andrew Project Archival
  • Legacy Academic Computing Research
PTI
Use PTI when…
  • Legacy Application Specific Workflows
  • Proprietary Image Storage

More comparisons

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