Roughness values from Blender need to be square rooted before being pulled in to Mitsuba

[AnsonSavage]

Summary:

This is what a scene looks like in Cycles:

I export the XML and render in Mitsuba and get:

It seemed a lot more rough. I tried square rooting each of the roughness values:

import mitsuba as mi
import math

# Set the Mitsuba variant for autodiff if needed
mi.set_variant('cuda_ad_rgb')

# 1. Load the Scene from an XML File
# scene = mi.load_file('scenes/geometry_no_emitters.xml')
scene = mi.load_file('scenes/geometry.xml')


scene_params['elm__3.bsdf.brdf_0.roughness.value'] = math.sqrt(float(scene_params['elm__3.bsdf.brdf_0.roughness.value'].numpy()[0]))
scene_params['elm__5.bsdf.brdf_0.roughness.value'] = math.sqrt(float(scene_params['elm__5.bsdf.brdf_0.roughness.value'].numpy()[0]))
scene_params['elm__7.bsdf.brdf_0.roughness.value'] = math.sqrt(float(scene_params['elm__7.bsdf.brdf_0.roughness.value'].numpy()[0]))
scene_params['elm__9.bsdf.brdf_0.roughness.value'] = math.sqrt(float(scene_params['elm__9.bsdf.brdf_0.roughness.value'].numpy()[0]))
scene_params.update()

image = mi.render(scene, spp=1024)

# Save the rendered image to a file
mi.util.write_bitmap('rendered_scene.png', image)

And then I get this, which seems to match Cycles pretty well:

So, should the roughness values from Blender simply be square rooted by default?

Environment (please complete the following information):

• OS: Windows 11
• Blender Version: 3.6.20
• Add-on Version: 0.4.0 (latest)

[bathal1]

Hi,
The remapping of the roughness is already handled by the add-on. Which BSDFs are you using in this example ?