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Image MIME Reference
JPEG-XS-(HEIF)

JPEG XS Image (HEIF Container)

image/jxsi
VS

Pentax Electronic File

image/x-pentax-pef
Pentax-PEF

A complete technical comparison of JPEG XS Image (HEIF Container) and Pentax Electronic File — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

Equal browser support

Feature Support

Feature JPEG-XS-(HEIF) Pentax-PEF
Transparency (Alpha) Yes ✕ No
Animation Support ✕ No ✕ No
Progressive Loading ✕ No ✕ No
HDR Support Yes Yes
EXIF Metadata Yes Yes
ICC Color Profile Yes Yes
JPEG XS Image (HEIF Container)
image/jxsi
Extension
.jxsi.jxs.hif
Container HEIF / ISOBMFF (ISO/IEC 23008-12)
Compression Lossy (Visually Lossless) / Mathematically Lossless
Algorithm
JPEG XS (ISO/IEC 21122-1)
Color Depth 8-bit, 10-bit, 12-bit, 14-bit, 16-bit
Developed by Joint Photographic Experts Group (JPEG)
Released 2019
Magic Bytes
XX XX XX XX 66 74 79 70 6A 78 73 69
Full JPEG-XS-(HEIF) reference →
Pentax Electronic File
image/x-pentax-pef
Extension
.pef
Container TIFF-based (Proprietary)
Compression Uncompressed / Proprietary Lossless
Algorithm
NonePentax Proprietary Lossless
Color Depth 12-bit (Per Channel), 14-bit (Per Channel)
Developed by Pentax (now Ricoh Imaging Company, Ltd.)
Released 2003
Magic Bytes
49 49 2A 00 (Little-endian) or 4D 4D 00 2A (Big-endian)
Full Pentax-PEF reference →

Browser Support Comparison

Browser JPEG-XS-(HEIF) Pentax-PEF
Chrome Chrome
✕ ✕
Firefox Firefox
✕ ✕
Safari Safari
✕ ✕
Edge Edge
✕ ✕
IE IE (Legacy)
✕ ✕
JPEG-XS-(HEIF)

JPEG-XS-(HEIF) Strengths

  • Provides sub-millisecond encoding and decoding latency while retaining visually lossless quality
  • Brings the extensive metadata, EXIF, XMP, and color-profiling capabilities of the HEIF container to JPEG XS
  • Allows grouping of multiple high-quality JPEG XS frames into a single collection file
Limitations
  • Zero web browser compatibility, limiting it entirely to professional and industrial hardware workflows
  • Extremely niche adoption compared to standard HEVC-based HEIC or raw JPEG XS codestreams
  • Requires custom parsing logic to extract the JPEG XS codestream from the HEIF boxes
Pentax-PEF

Pentax-PEF Strengths

  • Retains absolute maximum sensor data, enabling massive shadow recovery and highlight protection compared to compressed in-camera JPEGs
  • White balance and sharpening are saved as metadata instructions rather than 'baked in', meaning they can be perfectly adjusted in post-production
  • Utilizes the standard TIFF container structure, making it relatively straightforward for open-source software like LibRaw to parse
Limitations
  • Proprietary format requires continuous updates to third-party processing software whenever Pentax releases a new camera model (unlike the open DNG format)
  • Produces very large file sizes compared to standard web formats
  • Cannot be directly embedded into web pages or used in standard HTML/CSS contexts

When to choose which format

JPEG-XS-(HEIF)
Use JPEG-XS-(HEIF) when…
  • Live Broadcast Infrastructure
  • Medical Imaging & Archival
  • Video over IP Networks
  • Automotive & Drone Systems
Pentax-PEF
Use Pentax-PEF when…
  • Professional Digital Photography
  • Non-destructive Image Post-Processing
  • Pentax Camera Archival

More comparisons

JPEG-XS-(HEIF) vs ACES → Pentax-PEF vs ACES → JPEG-XS-(HEIF) vs APNG → Pentax-PEF vs APNG → JPEG-XS-(HEIF) vs AVCI → Pentax-PEF vs AVCI → JPEG-XS-(HEIF) vs AVCS → Pentax-PEF vs AVCS → JPEG-XS-(HEIF) vs AVIF → Pentax-PEF vs AVIF → All comparisons →
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