Maniphest T63938

Principled Shader - specular value 12.5
Confirmed, NormalKNOWN ISSUE
Actions

Assigned To
None
Authored By
Jacopo Chen (FloatingPoint)
Apr 27 2019, 3:59 PM
Tags
  • BF Blender
  • Cycles
  • Render & Cycles
Subscribers
Brecht Van Lommel (brecht)
Jacopo Chen (FloatingPoint)
Marco (nacioss)
Philipp Oeser (lichtwerk)

Description

System Information
Operating system: Arch Linux (kernel: 5.0.9-arch1-1-ARCH)
Graphics card: AMD Radeon R5 M255 (Iceland)

Blender Version
Broken: 2.79.7

Short description of error
Setting Specular value in Principled Shader to 12.5 causes the object to become much darker.

Exact steps for others to reproduce the error
Start Blender and switch to Cycles Render. Select the default cube and assign to its material a Principled BSDF (with default settings).
Change the specular value to exactly 12.5. In both the rendered mode and the material preview, the color darkens significantly compared to nearby values (like 12.499 and 12.501). If the Roughness slider is changed to 0.1, the cube becomes black.

Related Objects

Event Timeline

Jacopo Chen (FloatingPoint) created this task.Apr 27 2019, 3:59 PM
Marco (nacioss) added a subscriber: Marco (nacioss).Apr 28 2019, 3:31 PM

I can reproduce the issue, only at 12.5 of Specular it becomes black:


And changing roughness for me is changing from 0.016 to 0.020:

I'm in Ubuntu 18.04.2 using Blender 2.8 (2019-04-27) with an AMD RX 580

Philipp Oeser (lichtwerk) assigned this task to Brecht Van Lommel (brecht).Apr 29 2019, 10:22 AM
Philipp Oeser (lichtwerk) added a project: Cycles.
Philipp Oeser (lichtwerk) added subscribers: Brecht Van Lommel (brecht), Philipp Oeser (lichtwerk).

path_radiance_clamp_and_sum() asserts:

kernel_assert(!"Non-finite sum in path_radiance_clamp_and_sum!");

I guess a specular of 12.5 is highly non-realistic and looking at the IOR > specular formular here https://docs.blender.org/manual/en/dev/render/cycles/nodes/types/shaders/principled.html suggests this would be a out-of-reality specular value...
(Havent checked code, but 12.5 combined with the 0.08 value there comes to exactly 1 which might also be a hint why this goes wrong...)

@Brecht Van Lommel (brecht): could you check?

Philipp Oeser (lichtwerk) lowered the priority of this task from 90 to Normal.Apr 29 2019, 10:26 AM
Dalai Felinto (dfelinto) removed Brecht Van Lommel (brecht) as the assignee of this task.Dec 23 2019, 4:34 PM
Dalai Felinto (dfelinto) added a project: Tracker Curfew.
Brecht Van Lommel (brecht) changed the subtype of this task from "Report" to "Known Issue".Jan 27 2020, 12:15 PM
Brecht Van Lommel (brecht) edited projects, added Render & Cycles; removed Tracker Curfew.
tamooz br (Koopa512) mentioned this in T96719: Cycles: Principled BSDF: materials with Sepcular within close proximity to 12.5 are completely black.Aug 15 2022, 9:47 AM