Tone Mapping¶

flowchart LR
  A("ACES 
  RGB 
  Input") --> 
  B[ACES 
  to 
  JMh] --> 
  C["Tonescale 
  (J Only)"] --> 
  D["Chroma 
  Compression 
  (M Only)"] --> 
  E["Gamut 
  Compression 
  (J & M)"] --> 
  H["White
  Limiting"] --> 
  F["Display 
  Encoding"] --> 
  G(Display 
  RGB 
  Output);
  style C stroke-width:4px

Tone-mapping¶

After the data is in a JMh representation, the J channel is sent through the tone scale function.

Requirements¶

Here were a few of the key requirements considered when designing the tone mapping curve:

S-shaped: Tone scale shall have an "S-shaped" curve with a toe and shoulder.
Monotonic: Tone scale shall be continuously increasing over the domain.
Non-asymptotic: Tone scale shall not have any vertical or horizontal asymmptotes
Continuity: Tone scale shall be defined continuously over the domain.
Domain: Tone scale shall be defined for all float values.
Contrast: Tone scale shall have a log-log slope (gamma) through 18% mid-gray less than 1.55, which was the mid-slope contrast in ACES 1.
Dynamic Range: Tone scale shall provide the ability to produce consistent output for arbitrary dynamic ranges, but also provide preset values for common display setups, including:
- 48 nit cinema
- 100 nit video
- 108 nit Dolby Cinema
- 1000 nit HDR

Tone-mapping Function¶

The tone mapping function is based off a Michaelis-Mentin curve, and parameterized so that certain values can be calculated automatically based on the peak luminance value.

Values¶

	ACES value
Peak Luminance (nits)	0	0.18	1.0	2.0
100	0.000	10.000	45.757	63.988
500	0.000	13.193	89.098	158.949
1000	0.000	14.512	106.564	205.783
2000	0.000	15.747	121.664	248.779
4000	0.000	16.824	133.883	284.433