JPEG Network Graphics

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JPEG Network Graphics (JNG,

container format
to wrap JPEG-encoded image data.

JNG was created as an adjunct to the MNG animation format, but may be used as a stand-alone format. JNG files embed an 8-bit or 12-bit JPEG datastream in order to store color data, and may embed another datastream (1, 2, 4, 8, 16-bit PNG, or 8-bit JPEG grayscale image) for transparency information. However, a JNG may contain two separate JPEG datastreams for color information (one 8-bit and one 12-bit) to permit decoders that are unable to (or do not wish to) handle 12-bit datastreams to display the 8-bit datastream instead, if one is present.

Version 1.0 of the JNG specification was released on January 31, 2001 (initially as part of the MNG specification). Usually, all the applications supporting the MNG file format can handle JNG files too. For example,

Mozilla Firefox. The Mozilla Application Suite (and hence Netscape) originally supported MNG/JNG, but native support was removed in Mozilla 1.5a by developers, and Mozilla has not supported the format since. Safari
does not support MNG/JNG.

JNG enhances the capabilities of the

alpha channel
) can be saved either in lossless PNG format or in lossy JPEG format. This way, users can benefit from the power of JPEG compression while preserving lossless (PNG-compressed) transparency information.

The chunk-based structure of JNG files is essentially the same as that of PNG files, differing only in the slightly different signature and the use of different chunks.

Network Graphics signatures
Name Signature
hexadecimal ASCII + C0, C1
PNG 89 50 4E 47 0D 0A 1A 0A 0x80|
␊␚
␊
MNG 8A 4D 4E 47 0D 0A 1A 0A 0x80|␊MNG␍␊␚␊
JNG 8B 4A 4E 47 0D 0A 1A 0A 0x80|
␋
JNG␍␊␚␊

JNG does not have a registered

Internet media type, but image/x-jng can be used.[1]

Alternatives

Due to the lack of wide adoption of both the JNG and MNG format, it has fallen in disuse in favor of other formats that are in active development with similar qualities:

  • JPEG XR: Supporting wide color space and a lossy format with transparency (JNG contender, standardized)
  • WebP: Supporting a lossy format with transparency and animation (JNG/MNG contender, not yet standardized)
  • JPEG XL: Supporting wide color spaces, lossy and lossless encoding, animation and transparency (JPEG/PNG replacement contender)

Notes

  1. ^ Official JNG specification, section 1
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