https://draftdocs.acescentral.com/background/whats-new/

ACES 2.0 is the second major release of the components that make up the ACES system. The most significant change is a new suite of rendering transforms whose design was informed by collected feedback and requests from users of ACES 1. The changes aim to improve the appearance of perceived artifacts and to complete previously unfinished components of the system, resulting in a more complete, robust, and consistent product.

Highlights of the key changes in ACES 2.0 are as follows:

• New output transforms, including:
  • A less aggressive tone scale
  • More intuitive controls to create custom outputs to non-standard displays
  • Robust gamut mapping to improve perceptual uniformity
  • Improved performance of the inverse transforms
• Enhanced AMF specification
• An updated specification for ACES Transform IDs
• OpenEXR compression recommendations
• Enhanced tools for generating Input Transforms and recommended procedures for characterizing prosumer cameras
• Look Transform Library
• Expanded documentation
  

Rendering Transform

The most substantial change in ACES 2.0 is a complete redesign of the rendering transform.

ACES 2.0 was built as a unified system, rather than through piecemeal additions. Different deliverable outputs “match” better and making outputs to display setups other than the provided presets is intended to be user-driven. The rendering transforms are less likely to produce undesirable artifacts “out of the box”, which means less time can be spent fixing problematic images and more time making pictures look the way you want.

Key design goals

• Improve consistency of tone scale and provide an easy to use parameter to allow for outputs between preset dynamic ranges
• Minimize hue skews across exposure range in a region of same hue
• Unify for structural consistency across transform type
• Easy to use parameters to create outputs other than the presets
• Robust gamut mapping to improve harsh clipping artifacts
• Fill extents of output code value cube (where appropriate and expected)
• Invertible – not necessarily reversible, but Output > ACES > Output round-trip should be possible
• Accomplish all of the above while maintaining an acceptable “out-of-the box” rendering

http://lm-burns1114-dc.blogspot.co.nz/2012_10_01_archive.html