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Trying to reduce fireflies in a dark indoor scene, lit from hdr, the Blender manual suggests trying the Limited Global Illumination preset in light paths. (Using 2.92; manual is 2.93).

I confess I cannot understand how I am supposed to select one of the presets listed, nor which preset (if any) is the default setting. The options only show '-' signs. Does a particular object have to be selected? Does it not apply to filmic rendering?

I also tried with a fresh download of 2.93 and it comes up with errors, suggesting the default cannot be changed. Also the '+' sign reveals

Error: Python: Traceback (most recent call last):
       File "C:\Program Files\Blender Foundation\Blender 2.93\2.93\scripts\startup\bl_operators\presets.py", line 171, in execute
value = eval(rna_path)
File "<string>", line 1, in <module>
AttributeError: 'CyclesRenderSettings' object has no attribute 'blur_glossycycles'

location: <unknown location>:-1

How do I change it, or can I not?

This question:

No "full global illumination" option in light path settings in Cycles?

helped me find the integrator scripts at Blender/2.93/scripts/presets/cycles/integrator/full_global_illumination.py and /limited_global_illumination.py.

This gives me a better understanding of what presets are, but leads me to imagine that the presets panel should be able to call one of the scripts?

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  • $\begingroup$ I see I'm thinking backwards; is it rather that changing a setting enables the change to be stored as a new preset in a script? $\endgroup$
    – koober
    Jun 25, 2021 at 15:55

1 Answer 1

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This seems to be a long-running problem, on and off, since 2.80. I notice that the behaviour is different even between 2.92.0 and 2.93.1.

https://developer.blender.org/T62325
"Clicking Preset doesn't change the settings immediately"

Yet in 2.93 more scripts are available, and the settings can be experimented with manually.

Scripts available are as follows:

import bpy
cycles = bpy.context.scene.cycles

# Default.py
cycles.max_bounces = 12
cycles.caustics_reflective = True
cycles.caustics_refractive = True
cycles.diffuse_bounces = 4
cycles.glossy_bounces = 4
cycles.transmission_bounces = 12
cycles.volume_bounces = 0
cycles.transparent_max_bounces = 8
cycles.use_fast_gi = False
cycles.ao_bounces = 1
cycles.ao_bounces_render = 1

#Direct_Light.py
cycles.max_bounces = 8
cycles.caustics_reflective = False
cycles.caustics_refractive = False
cycles.diffuse_bounces = 0
cycles.glossy_bounces = 1
cycles.transmission_bounces = 2
cycles.volume_bounces = 0
cycles.transparent_max_bounces = 8
cycles.use_fast_gi = False
cycles.ao_bounces = 1
cycles.ao_bounces_render = 1

# Fast_Global_Illumination.py
cycles.max_bounces = 8
cycles.caustics_reflective = False
cycles.caustics_refractive = False
cycles.diffuse_bounces = 1
cycles.glossy_bounces = 4
cycles.transmission_bounces = 8
cycles.volume_bounces = 2
cycles.transparent_max_bounces = 8
cycles.use_fast_gi = True
cycles.ao_bounces = 2
cycles.ao_bounces_render = 2

# Full_Global_Illumination.py
cycles.max_bounces = 32
cycles.caustics_reflective = True
cycles.caustics_refractive = True
cycles.diffuse_bounces = 32
cycles.glossy_bounces = 32
cycles.transmission_bounces = 32
cycles.volume_bounces = 32
cycles.transparent_max_bounces = 32
cycles.use_fast_gi = False
cycles.ao_bounces = 1
cycles.ao_bounces_render = 1

# Limited_Global_Illumination.py
cycles.max_bounces = 8
cycles.caustics_reflective = False
cycles.caustics_refractive = False
cycles.diffuse_bounces = 1
cycles.glossy_bounces = 4
cycles.transmission_bounces = 8
cycles.volume_bounces = 0
cycles.transparent_max_bounces = 8
cycles.use_fast_gi = False
cycles.ao_bounces = 1
cycles.ao_bounces_render = 1
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