Free webp to jpg
EN
Image MIME Reference
JNG

JPEG Network Graphics

image/x-jng
VS

Portable Anymap

image/x-portable-anymap
PNM

A complete technical comparison of JPEG Network Graphics and Portable Anymap — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

Equal browser support

Feature Support

Feature JNG PNM
Transparency (Alpha) Yes ✕ No
Animation Support ✕ No ✕ No
Progressive Loading Yes ✕ No
HDR Support ✕ No ✕ No
EXIF Metadata Yes ✕ No
ICC Color Profile Yes ✕ No
JPEG Network Graphics
image/x-jng
Extension
.jng
Container PNG-style Chunk Structure (JHDR, JDAT, IDAT, IEND)
Compression Lossy (JPEG/DCT for color) / Lossless (Deflate for alpha mask)
Algorithm
JPEG (Discrete Cosine Transform)Deflate (LZ77)
Color Depth 8-bit, 12-bit, 24-bit (RGB), 32-bit (RGBA)
Developed by MNG Development Group (Glenn Randers-Pehrson et al.)
Released 2001
Magic Bytes
8B 4A 4E 47 0D 0A 1A 0A
Full JNG reference →
Portable Anymap
image/x-portable-anymap
Extension
.pnm
Container Netpbm
Compression Uncompressed
Algorithm
None
Color Depth 1-bit (PBM), 8-bit to 16-bit (PGM), 24-bit to 48-bit (PPM)
Developed by Jef Poskanzer (Netpbm Project)
Released 1988
Magic Bytes
50 31, 50 32, 50 33, 50 34, 50 35, or 50 36
Full PNM reference →

Browser Support Comparison

Browser JNG PNM
Chrome Chrome
✕ ✕
Firefox Firefox
✕ ✕
Safari Safari
✕ ✕
Edge Edge
✕ ✕
IE IE (Legacy)
✕ ✕
JNG

JNG Strengths

  • Solved a massive technical hurdle in the early 2000s by combining high-compression lossy photographic data with crisp, 8-bit alpha transparency
  • Utilized the highly robust, extensible chunk-based architecture of the PNG format
  • Provided an excellent, bandwidth-saving alternative to massive 32-bit transparent PNGs for web design
Limitations
  • Failed to achieve critical mass; browser vendors largely abandoned the MNG/JNG standard due to implementation complexity
  • Completely obsolete today, having been superseded by natively supported, superior formats like WebP, AVIF, and HEIC
  • Decoding requires a hybrid engine that can parse PNG chunks while simultaneously decoding a JPEG stream and a Deflate stream, complicating software support
PNM

PNM Strengths

  • Unparalleled simplicity: parsers and writers for PNM files can be written from scratch in C or Python in just a few minutes without relying on external libraries
  • Serves as an excellent foundational teaching tool for computer science students learning about image arrays and raster graphics
  • Flawlessly pipes through Unix command-line utilities for robust automated image processing (via the Netpbm suite)
Limitations
  • Zero compression natively results in astronomical file sizes, making it entirely impractical for web delivery or consumer storage
  • No support for standard metadata formats like EXIF, XMP, or ICC color profiles
  • No native alpha channel support in the classic PNM specification (though the newer PAM format 'P7' addresses this)

When to choose which format

JNG
Use JNG when…
  • Embedded frames in MNG animations
  • Historical web graphics requiring lossy compression with transparency
PNM
Use PNM when…
  • Unix/Linux Command-Line Image Processing (Netpbm suite)
  • Academic Computer Vision Research
  • Intermediary Format for Image Format Conversion

More comparisons

JNG vs ACES → PNM vs ACES → JNG vs APNG → PNM vs APNG → JNG vs AVCI → PNM vs AVCI → JNG vs AVCS → PNM vs AVCS → JNG vs AVIF → PNM vs AVIF → All comparisons →
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