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Allow subsurface_radius_scale to go above 1 #268

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Allow subsurface_radius_scale to go above 1 #268

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553e591
Allow subsurface_radius_scale to go above 1
peterkutz Jul 29, 2025
38ecbbb
Adjust/fix formatting/alignment
peterkutz Jul 29, 2025
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14 changes: 7 additions & 7 deletions index.html
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Expand Up @@ -745,13 +745,13 @@
Note that the default value of **`subsurface_radius_scale`** is set at $(1, 0.5, 0.25)$ to approximate the effect of Rayleigh scattering. If we roughly approximate the wavelength corresponding to each of the RGB channels as $\lambda/\mathrm{nm} \approx 650, 550, 450$ and assume the radii scale like the reciprocal of the extinction, then since in Rayleigh scattering the extinction scales like $\lambda^{-4}$ for light of wavelength $\lambda$ the expected relative magnitudes of the radii are $(1, (550/650)^4, (450/650)^4) \approx (1, 0.5, 0.25)$, hence the chosen default. This provides a slightly more realistic default look for the subsurface than resulting from gray radii.


Subsurface params | Label | Type | Range | Norm | Default | Description
------------------------------------|--------------|-----------|:---------------:|:----------:|:--------------------:|----------------------------------------------
**`subsurface_weight`** | Weight | `float` | $ [0, 1] $ | | $ 0 $ | Mix weight between subsurface and diffuse slabs
**`subsurface_color`** | Color | `color3` | $ [0, 1] $ | | $ (0.8, 0.8, 0.8) $ | The observed reflection color of $V^\infty_\mathrm{subsurface}$
**`subsurface_radius`** | Radius | `float` | $ [0, \infty) $ | $ [0, 1] $ | $ 1 $ | Length scale of MFP
**`subsurface_radius_scale`** | Radius scale | `color3` | $ [0, 1]^3 $ | | $ (1.0, 0.5, 0.25) $ | RGB multiplier to **`subsurface_radius`**, giving the per-channel MFPs
**`subsurface_scatter_anisotropy`** | Anisotropy | `float` | $ [-1, 1] $ | | $ 0 $ | Anisotropy of the Henyey--Greenstein phase function of the interior medium $V^\infty_\mathrm{subsurface}$
Subsurface params | Label | Type | Range | Norm | Default | Description
------------------------------------|--------------|-----------|:-----------------:|:------------:|:--------------------:|----------------------------------------------
**`subsurface_weight`** | Weight | `float` | $ [0, 1] $ | | $ 0 $ | Mix weight between subsurface and diffuse slabs
**`subsurface_color`** | Color | `color3` | $ [0, 1] $ | | $ (0.8, 0.8, 0.8) $ | The observed reflection color of $V^\infty_\mathrm{subsurface}$
**`subsurface_radius`** | Radius | `float` | $ [0, \infty) $ | $ [0, 1] $ | $ 1 $ | Length scale of MFP
**`subsurface_radius_scale`** | Radius scale | `color3` | $ [0, \infty)^3 $ | $ [0, 1]^3 $ | $ (1.0, 0.5, 0.25) $ | RGB multiplier to **`subsurface_radius`**, giving the per-channel MFPs
**`subsurface_scatter_anisotropy`** | Anisotropy | `float` | $ [-1, 1] $ | | $ 0 $ | Anisotropy of the Henyey--Greenstein phase function of the interior medium $V^\infty_\mathrm{subsurface}$

![](images/subsurface1.jpg width=99%) ![](images/subsurface2.jpg width=99%) ![](images/subsurface3.jpg width=99%)
<div class="shifted-caption">
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4 changes: 2 additions & 2 deletions parametrization.md.html
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Expand Up @@ -44,7 +44,7 @@
| `subsurface_weight` | Weight | `float` | $ [0, 1] $ | | $ 0 $ | |
| `subsurface_color` | Color | `color3` | $ [0, 1] $ | | $ (0.8, 0.8, 0.8) $ | |
| `subsurface_radius` | Radius | `float` | $ [0, \infty) $ | $ [0, 1] $ | $ 1 $ | length |
| `subsurface_radius_scale` | Radius scale | `color3` | $ [0, 1]^3 $ | | $ (1.0, 0.5, 0.25) $ | |
| `subsurface_radius_scale` | Radius scale | `color3` | $ [0, \infty)^3 $ | $ [0, 1]^3 $ | $ (1.0, 0.5, 0.25) $ | |
| `subsurface_scatter_anisotropy` | Anisotropy | `float` | $ [-1, 1] $ | | $ 0 $ | |
| **Coat** |
| `coat_weight` | Weight | `float` | $ [0, 1] $ | | $ 0 $ | |
Expand All @@ -62,7 +62,7 @@
| `emission_color` | Color | `color3` | $ [0, 1]^3 $ | | $ (1, 1, 1) $ | |
| **Thin-film** |
| `thin_film_weight` | Weight | `float` | $ [0, 1] $ | | $ 0 $ | |
| `thin_film_thickness` | Thickness | `float` | $ [0, \infty) $ | $ [0, 1] $ | $ 0.5 $ | $\mathrm{\mu m}$ |
| `thin_film_thickness` | Thickness | `float` | $ [0, \infty) $ | $ [0, 1] $ | $ 0.5 $ | $\mathrm{\mu m}$ |
| `thin_film_ior` | IOR | `float` | $ (0, \infty) $ | $ [1, 3] $ | $ 1.4 $ | |
| **Geometry** |
| `geometry_opacity` | Opacity | `float` | $ [0, 1] $ | | $ 1 $ | |
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