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Image MIME Reference
CMU-Raster

CMU Window Manager Raster

image/x-cmu-raster
VS

SealedMedia Portable Network Graphics

image/vnd.sealed.png
Sealed-PNG

A complete technical comparison of CMU Window Manager Raster and SealedMedia Portable Network Graphics — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

Equal browser support

Feature Support

Feature CMU-Raster Sealed-PNG
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 →
SealedMedia Portable Network Graphics
image/vnd.sealed.png
Extension
.spng.sealed-png
Container SealedMedia / Oracle IRM Wrapper
Compression Encrypted Payload (Deflate)
Algorithm
AES EncryptionDeflate (Internal PNG payload)
Color Depth Encrypted Payload
Developed by SealedMedia (Acquired by Oracle Corporation)
Released Late 1990s / Early 2000s
Magic Bytes
Unknown (Proprietary SealedMedia Container)
Full Sealed-PNG reference →

Browser Support Comparison

Browser CMU-Raster Sealed-PNG
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
Sealed-PNG

Sealed-PNG Strengths

  • Provided absolute control over intellectual property, allowing enterprise administrators to instantly revoke viewing rights of a local file globally
  • Detailed audit trails tracked exactly who opened the image, when, and from what IP address
Limitations
  • Completely proprietary and relies on a central authentication server; if the server goes offline, the image is permanently inaccessible
  • No support in modern operating systems, web browsers, or standard image editing software without installing heavy enterprise DRM clients
  • Oracle effectively deprecated the IRM product line, leaving legacy sealed documents difficult to recover

When to choose which format

CMU-Raster
Use CMU-Raster when…
  • Historical UNIX / Andrew Project Archival
  • Legacy Academic Computing Research
Sealed-PNG
Use Sealed-PNG when…
  • Enterprise Information Rights Management (IRM)
  • Secure Corporate Intellectual Property Distribution
  • Revocable Medical or Legal Imaging

More comparisons

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