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View Full Version : Your tricks to avoid sblotchies in GI ?



madno
09-21-2015, 12:05 AM
Hi,

had a scene that needed to be large (approx. 2,5 meter x 2 meter). Worked well but I did not like the splotchies in some areas.

Surface = all reflective with some blurr (no LW specular)
Light = all via HDR sphere
Light2 = One area light (single sided) to make far distance white.

Ray Recursion = 10
Shading and Light samples = 1

Global:
Intensity = 100
Indirect Bounces = 2
Rays per Evolution = 350
Secondary Rays = 64
Angular = 45
Minimum pixel = 1
Maximun pixel = 200

Camera:
Width 11810
Height 14394

Minimum Samples = 1
Maximum Samples = 128

Threshold = 0.01

Filter = Mitchel
Pattern = Low-Discrpancy


Do I need to throw more GI samples at it to get rid of the splochyness, or is there another trick to do this?
(render time was already 6+ hours).

129830
best seen at 1:1

EDIT: upps, typo on the headline. Seems so one can't edit that ?

djwaterman
09-21-2015, 02:38 AM
It is my understanding that you'd need to add more RPE, try 600, secondary rays could be lowered as they don't make a huge difference, and perhaps your HDR (one being used for GI) could be blurred if it isn't already, You can have an un-blurred one for reflections that isn't contributing to GI.

If it's for a still, you could render just those problem areas with limited region using the higher settings and paste them in Photoshop.

Check out that EXCEPT radiosity guide http://www.except.nl/lightwave/RadiosityGuide95/, cos that's where I'm getting my information.

Danner
09-21-2015, 03:56 AM
Yeah your samples are too low, 600 RPE and 300 secondary. Try with minimum pixel spacing 3 and maximum 100 it should speed things up a little but you might lose a little of the occlusion effect.

Now for the real time saving trick:
Activate the cache for radiosity, give it a name, now in the render pannel turn off reflection and refraction, since you are rendering a still make sure your render range is frame 1 to 1. then back to the global illumination tab click on "bake radiosity scene" when that is done, lock the cache by changing the preprocess method. Turn reflexion and refraciton back on and hit F9. Get the idea? =) You can also exclude reflections from the radiosity calculation with nodes on a per surface basis but this is easier.

RebelHill
09-21-2015, 04:45 AM
https://www.youtube.com/watch?v=0YFZ2av-BLg&list=PL8A1C0DB658775A63&index=2

JonW
09-21-2015, 06:19 AM
See my comment #15

http://forums.newtek.com/showthread.php?139689-Trouble-rendering-realistic-scene

Danner
09-21-2015, 08:03 AM
You might know this but just in case: You mentioned that you are lighting using an HDR image, it should different from the reflected HDR and it should be low rez and blured to lessen splotches caused by it.

vonpietro
09-21-2015, 09:22 AM
minimum spacing should be 1 - somewhat less flicker and splotch in animations

and

bake extra cameras - with bake radiosity

set a camera right where the splotch is - aim the camera at it - hit bake radiosity -
not sure if you need a solution already - and then add but probable best that way.

this is what i got from the rebel hill video - that video is a must watch for anyone using radiosity -
super awesome info - thanks

Surrealist.
09-21-2015, 01:43 PM
Additionally this guide is useful:

http://www.except.nl/lightwave/RadiosityGuide96/index.htm

Dan Ritchie
09-21-2015, 04:18 PM
Additionally this guide is useful:

http://www.except.nl/lightwave/RadiosityGuide96/index.htm

This may be the unpopular answer, but use brute force so you can get away with less lighting samples. This eliminates blotchiness in favor of grain that is more natural looking. I do this sometimes and render times are better in certain cases.

vonpietro
09-21-2015, 04:52 PM
surrealist-
that is
one heck of a guide
not to mention beyond useful - it's required reading

OjN
09-21-2015, 06:34 PM
new:

- Try 4-8 light samples! (my recipe for better area light soft shadows)
- Render Globals: Render: On noise reduction, Gaussian HDR filtering
- Angular = 20- 10
- Filter = Soft Mitchel
- use Gerardo denoiser node setup: http://forums.newtek.com/showthread.php?146003-Gerardo-Estrada-DPont-Denoiser&highlight=denoiser+dpont+gerardo

OjN
09-21-2015, 06:43 PM
Also you can use:

render: global illumination: Multiplier: 150-300 . See Except guide, basically you multiply your specs x1,5-3 and your times...

Surrealist.
09-21-2015, 11:28 PM
surrealist-
that is
one heck of a guide
not to mention beyond useful - it's required reading

Agreed. :)

madno
09-22-2015, 12:12 AM
Thanks for the input.
Like expected more RPE are required (angular, bounces, max pixel size, secondary rays, etc all do not make a big difference). At 1000 it starts to get ok. But that would lead to too long render times.
Will try the baking camera next time as the problematic areas are easy to spot (never tried that).
All the other tricks were already incorporated (refl etc. off via schlick node, welded geo, blurred hdr).
By the way, I tried brute force GI on a tiny limited region with 2015.3 on Win 10 - result = crash in the middle of the render.

erikals
09-22-2015, 12:34 AM
haven't tried the DP DeNoiser yet, sure looks interesting though... >
http://forums.newtek.com/showthread.php?146003-Gerardo-Estrada-DPont-Denoiser