GT — Uchimura Tone Mapper
The GT (Grand Turismo) tone mapper was created by Hajime Uchimura at Polyphony Digital and presented at CEDEC 2017 ("HDR theory and practice"). It offers the most granular control of any operator in this plugin, with separate parameters for the toe, linear section, and shoulder of the curve.
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How it works
The curve is split into three regions and blended with smooth weights:
- Toe — a power-law darkening of the shadows
- Linear — the central ramp (slope =
a) - Shoulder — exponential roll-off approaching max brightness
P
Applied per-channel (R, G, B independently).
Settings reference
| Setting | Default | Range | Description |
|---|---|---|---|
| Max Brightness (P) | 1.0 | > 0 | Maximum displayable brightness. Values above 1.0 compress more of the HDR range. |
| Contrast (a) | 1.0 | > 0 | Slope of the linear section. Higher = steeper midtones. |
| Linear Start (m) | 0.22 | [0, 1] | Input value where the linear section begins (end of the toe). |
| Linear Length (l) | 0.4 | [0, 1] | Fraction of the range covered by the linear section. |
| Black Tightness (c) | 1.33 | > 0 | Power applied to the toe. Higher = tighter, punchier shadows. |
| Pedestal (b) | 0.0 | ≥ 0 | Lift added to the shadow toe — useful to avoid pure black crushing. |
The defaults reproduce Uchimura's original reference settings as presented at CEDEC 2017.
Tuning guide
Increasing contrast in midtones — Raise Contrast (a). Compensate with a lower Linear Start if the image gets too bright overall.
Softer highlights — Lower Max Brightness (P) or shorten Linear Length (l) to push the shoulder earlier.
Richer shadows — Raise Black Tightness (c) toward 2.0. Keep Pedestal at 0.0 for maximum depth.
Cinematic fog lift — Set Pedestal (b) to 0.01–0.05 to get a subtle crush-free shadow floor, similar to a film print.
When to use GT
- When you need precise per-zone control over the tone response
- Cinematics where art-directed curve shaping is required
- As a starting point to replicate a reference reference photograph's tonal response
Uchimura GT: CEDEC 2017 slides — "HDR theory and practice", Hajime Uchimura, Polyphony Digital.