# What does the ACES 2.0 tone scale do, which constants define it, and what changed from the ACES 1.x RRT (glow, red modifier, global desaturation) that sat before its tone curve?

- id: art_01M5NE1TCGJE7PNVD4TXZ9CS0N
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T12 · tags: none
- updated: 2026-10-23T22:28:07.176Z
- url: https://veyrul.com/articles/art_01M5NE1TCGJE7PNVD4TXZ9CS0N

The ACES 2 docs require a monotonic S-shaped tone scale with mid-grey log-log slope below ACES 1's 1.55, presets for 48/100/108/1000 nits and a Michaelis-Menten-based curve, and tabulate 18% grey output of 10.000 nits at 100 nits and 14.512 at 1000 nits; the ACES 2 CTL sets c_d = 10.013 for 18% grey output; ACES 1.3.1's RRT used glow (0.05/0.08), red modifier (0.82) and 0.96 global desaturation. Licence texts differ by tag: Apache-2.0 at aces-core 069b0bc3, Academy ACES component terms at the 1.3.1 commit fc189808.

The ACES 2 docs require a monotonic S-shaped tone scale with mid-grey log-log slope below ACES 1's 1.55, presets for 48/100/108/1000 nits and a Michaelis-Menten-based curve, and tabulate 18% grey output of 10.000 nits at 100 nits and 14.512 at 1000 nits; the ACES 2 CTL sets c_d = 10.013 for 18% grey output; ACES 1.3.1's RRT used glow (0.05/0.08), red modifier (0.82) and 0.96 global desaturation. Licence texts differ by tag: Apache-2.0 at aces-core 069b0bc3, Academy ACES component terms at the 1.3.1 commit fc189808.

Curator qualifications: Docs 10.000 vs CTL 10.013 for 100-nit grey: close but not identical; whether CTL output equals the table value is not established (producer synthesis agrees). Forum statements (S40, S46) and v1-feedback doc (S11) not reinspected. Licence differs by version; cite per version. Static reading; no transform evaluated.

Limitations: Static reading; no transform evaluated.

Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

```json
{
  "citations": [
    {
      "url": "https://raw.githubusercontent.com/aces-aswf/aces-docs/7c34c2100c8da55cd6f94301125d57e38079fc62/docs/background/v1-feedback.md",
      "note": "aces-docs tone-mapping/index.md lines 39-98 at 7c34c210 (SPDX CC-BY-4.0); aces-core lib/Lib.Academy.Tonescale.ctl lines 36-39 at 069b0bc3; ACES 1.3.1 transforms/ctl/lib/ACESlib.RRT_Common.ctl lines 12-23, 143 at fc189808; aces-core LICENSE at 069b0bc3; aces-core LICENSE.md at fc189808 (ACES 1.3.1)"
    },
    {
      "url": "https://raw.githubusercontent.com/aces-aswf/aces-core/069b0bc3e1f6c62820f19fdae2fecec3f4fc0f80/lib/Lib.Academy.Tonescale.ctl",
      "note": "aces-docs tone-mapping/index.md lines 39-98 at 7c34c210 (SPDX CC-BY-4.0); aces-core lib/Lib.Academy.Tonescale.ctl lines 36-39 at 069b0bc3; ACES 1.3.1 transforms/ctl/lib/ACESlib.RRT_Common.ctl lines 12-23, 143 at fc189808; aces-core LICENSE at 069b0bc3; aces-core LICENSE.md at fc189808 (ACES 1.3.1)"
    },
    {
      "url": "https://raw.githubusercontent.com/aces-aswf/aces-core/fc189808208e28019a8c5a27cdb2d50312939232/transforms/ctl/lib/ACESlib.RRT_Common.ctl",
      "note": "aces-docs tone-mapping/index.md lines 39-98 at 7c34c210 (SPDX CC-BY-4.0); aces-core lib/Lib.Academy.Tonescale.ctl lines 36-39 at 069b0bc3; ACES 1.3.1 transforms/ctl/lib/ACESlib.RRT_Common.ctl lines 12-23, 143 at fc189808; aces-core LICENSE at 069b0bc3; aces-core LICENSE.md at fc189808 (ACES 1.3.1)"
    },
    {
      "url": "https://raw.githubusercontent.com/aces-aswf/aces-docs/7c34c2100c8da55cd6f94301125d57e38079fc62/docs/system-components/output-transforms/index.md",
      "note": "aces-docs tone-mapping/index.md lines 39-98 at 7c34c210 (SPDX CC-BY-4.0); aces-core lib/Lib.Academy.Tonescale.ctl lines 36-39 at 069b0bc3; ACES 1.3.1 transforms/ctl/lib/ACESlib.RRT_Common.ctl lines 12-23, 143 at fc189808; aces-core LICENSE at 069b0bc3; aces-core LICENSE.md at fc189808 (ACES 1.3.1)"
    },
    {
      "url": "https://community.acescentral.com/t/5734",
      "note": "aces-docs tone-mapping/index.md lines 39-98 at 7c34c210 (SPDX CC-BY-4.0); aces-core lib/Lib.Academy.Tonescale.ctl lines 36-39 at 069b0bc3; ACES 1.3.1 transforms/ctl/lib/ACESlib.RRT_Common.ctl lines 12-23, 143 at fc189808; aces-core LICENSE at 069b0bc3; aces-core LICENSE.md at fc189808 (ACES 1.3.1)"
    },
    {
      "url": "https://community.acescentral.com/t/5970",
      "note": "aces-docs tone-mapping/index.md lines 39-98 at 7c34c210 (SPDX CC-BY-4.0); aces-core lib/Lib.Academy.Tonescale.ctl lines 36-39 at 069b0bc3; ACES 1.3.1 transforms/ctl/lib/ACESlib.RRT_Common.ctl lines 12-23, 143 at fc189808; aces-core LICENSE at 069b0bc3; aces-core LICENSE.md at fc189808 (ACES 1.3.1)"
    },
    {
      "url": "https://raw.githubusercontent.com/aces-aswf/aces-docs/7c34c2100c8da55cd6f94301125d57e38079fc62/docs/system-components/output-transforms/technical-details/tone-mapping/index.md",
      "note": "aces-docs tone-mapping/index.md lines 39-98 at 7c34c210 (SPDX CC-BY-4.0); aces-core lib/Lib.Academy.Tonescale.ctl lines 36-39 at 069b0bc3; ACES 1.3.1 transforms/ctl/lib/ACESlib.RRT_Common.ctl lines 12-23, 143 at fc189808; aces-core LICENSE at 069b0bc3; aces-core LICENSE.md at fc189808 (ACES 1.3.1)"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] The ACES 2 docs require a monotonic S-shaped tone scale with mid-grey log-log slope below ACES 1's 1.55, presets for 48/100/108/1000 nits and a Michaelis-Menten-based curve, and tabulate 18% grey output of 10.000 nits at 100 nits and 14.512 at 1000 nits; the ACES 2 CTL sets c_d = 10.013 for 18% grey output; ACES 1.3.1's RRT used glow (0.05/0.08), red modifier (0.82) and 0.96 global desaturation. Licence texts differ by tag: Apache-2.0 at aces-core 069b0bc3, Academy ACES component terms at the 1.3.1 commit fc189808. · locator: aces-docs tone-mapping/index.md lines 39-98 at 7c34c210 (SPDX CC-BY-4.0); aces-core lib/Lib.Academy.Tonescale.ctl lines 36-39 at 069b0bc3; ACES 1.3.1 transforms/ctl/lib/ACESlib.RRT_Common.ctl lines 12-23, 143 at fc189808; aces-core LICENSE at 069b0bc3; aces-core LICENSE.md at fc189808 (ACES 1.3.1) · source: https://raw.githubusercontent.com/aces-aswf/aces-docs/7c34c2100c8da55cd6f94301125d57e38079fc62/docs/background/v1-feedback.md

Rights:
- documentation: license=unknown hosting=permitted redistribution=permitted modification=unknown training=unknown · Applies to this original summary only, not to the cited sources.

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