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Image MIME Reference
HEIF

High Efficiency Image File Format

image/heif
VS

SealedMedia Portable Network Graphics

image/vnd.sealed.png
Sealed-PNG

A complete technical comparison of High Efficiency Image File Format 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 HEIF Sealed-PNG
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
High Efficiency Image File Format
image/heif
Extension
.heif.hif
Container HEIF / ISOBMFF (ISO/IEC 14496-12)
Compression Lossy / Lossless
Algorithm
Codec Agnostic (HEVC, AVC, JPEG, AV1)
Color Depth 8-bit, 10-bit, 12-bit, 16-bit
Developed by Moving Picture Experts Group (MPEG)
Released 2015
Magic Bytes
XX XX XX XX 66 74 79 70 6D 69 66 31
Full HEIF 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 HEIF Sealed-PNG
Chrome Chrome
✕ ✕
Firefox Firefox
✕ ✕
Safari Safari
✕ ✕
Edge Edge
✕ ✕
IE IE (Legacy)
✕ ✕
HEIF

HEIF Strengths

  • Highly flexible container that can store image bursts, animations, focal stacks, and stereo 3D images in one file
  • Natively supports depth maps and alpha channels, making it perfect for computational photography
  • When paired with modern codecs like HEVC or AV1, it provides massive storage savings over legacy formats like JPEG
Limitations
  • Codec agnosticism makes broad software decoding difficult, as the container might hold proprietary or unsupported codecs
  • Zero cross-platform web browser support, requiring conversion for online publishing
  • Often confused with the more specific 'image/heic' and 'image/avif' MIME types
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

HEIF
Use HEIF when…
  • Digital Photography
  • Camera Capture
  • Image Archiving
  • Multi-image composites
Sealed-PNG
Use Sealed-PNG when…
  • Enterprise Information Rights Management (IRM)
  • Secure Corporate Intellectual Property Distribution
  • Revocable Medical or Legal Imaging

More comparisons

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