JPEG XT

JPEG XT is an extension of the JPEG and JPEG-HDR graphics formats. It offers higher bit depths, high dynamic range, lossless and near-lossless compression, and transparency.

As of 2015-11, it is apparently still in development, though Part 1 of the standard has been published.

Specifications
The documents listed here are not necessarily available yet, and if they are, they're probably not free to download.
 * ISO/IEC 18477-1:2015 - Part 1: Scalable compression and coding of continuous-tone still images
 * ISO/IEC 18477-1 preview
 * ISO/IEC PRF 18477-2 - Part 2: Extensions for high dynamic range images
 * ISO/IEC 18477-3 - Part 3: Box file format
 * ISO/IEC CD 18477-4 - Part 4: Conformance testing
 * ISO/IEC CD 18477-5 - Part 5: Reference software
 * ISO/IEC FDIS 18477-6 - Part 6: IDR Integer Coding
 * ISO/IEC FDIS 18477-7 - Part 7: HDR Floating-Point Coding
 * ISO/IEC DIS 18477-8 - Part 8: Lossless and Near-lossless Coding
 * ISO/IEC DIS 18477-9 - Part 9: Alpha Channel Coding

Software

 * Software for JPEG XT
 * Thomas Richter's libjpeg

Links

 * Overview of JPEG XT