Vray, GI flickering animation

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Old 11 November 2013   #1
Vray, GI flickering animation

Hey guys, I've attached a render so you can see what the environment looks like. The modeling and texturing is not done but I'm trying to finalize my render settings for later by rendering while I sleep.

The problem is I'm still getting some GI flickering and swimming. I've circled in red the most obvious areas but really the GI is moving around for all surfaces and obviously flickering at the tops of all window frames. I'm pretty sure its my render settings. Now my render times are starting to get high so I'm asking for your help in hopes are dialling in the right value to stop this from happening as it's the last remaining render flaw I have to deal with. Below are my settings;

Vray
Image Sampler - Adaptive DMC
AA filter Gaussian with a size of 2.0. Min subdivs-1 max subdivs-8. Threshold - .010

Color mapping
Type- Linear multiply
Gamma 2.2
Affect background - on

Vray Sun and Sky - on

Camera type - Movie Camera (all other setting default except FOV -65)

Indirect Illumination
GI-on
Ambient Occlusion - on, multiplier 1.5, radius 50, subdiv 8
Primary bounces - Irradiance map
Secondary bounces - Light cache
Irradiance map- Present Medium animation
Light cache- # of passes 24, subdivs 1500, sample size .020, use light cache for glossy rays ON. Mode - Single Frame

Settings
DMC Sampler
Adaptive Amount - 1.0
System - Raycaster params - Dynamic memory limit 15000

I'm using maya 2013 sp2 with Vray 2.30.01. My box has 24 gigs of ram. My final render size will be HD1080.

There are 2 short scenes that involve objects moving. Before the attached shot a double gate door will open for 3 seconds. Then it's a fly-through down that cobblestone path. At the end of the cobblestone path a car will be moving around for 5 seconds.
 
Old 11 November 2013   #2
Hey Buzert

Try to determine your time budget per frame and how far you can go.

You can try a lower value for your threshold. You will probably don't hate to go lower than
.005

Try to use brute force for your secondary bounce.

What is your light and shader sample ? maybe you will need more than 8 sample for your shadow.

best luck !
 
Old 11 November 2013   #3
I really really think it has something to do with the GI. But the answers to your questions are below;

VraySun Shadow subdivs-5
I don't know how to find the light sample...I'm only using the sun.

Okay I've getting mixed feedback on what GI settings to use in my situation. So far 2 people have agreed that Irradiance map is what I should use for Primary. For secondary I've been told Light cache and Brute force. There must be a standard combination that works best for camera flythrough with some animated objects?
 
Old 11 November 2013   #4
The easy way would be to switch primary bounce to brute force. Keep the light cache as secondary.

If you want it to render faster, I'd recommend this work flow.

1.1 IR primary and LC secondary for static objects.
1.2 bake IR map for static objects in 1 single map using "Add to current map" mode. Move your time line around so that the IR map would cover everything. Doesn't need to be every frame.
1.3 Once you have your IR map, switch to "from file" mode. Put your moving objects into a V-Ray object property. Have them cast shadows but don't receive/generate GI.
1.4 Render

2.1 Use brute force primary LC secondary for your moving objects.
2.2 This time put everything else in another V-ray object property. Make them a matte while generating and receive GI.
2.3 Render.

Matte objects and V-ray object property can be really powerful, play with it
 
Old 11 November 2013   #5
I have rendered a lot of sometimes very complex lighting scenarios in Vray without any flickering at all, and it is extremely simple.

Use brute force as primary GI and light cache as secondary one. Make sure you do not use light cache for glossy reflections and that sudbdivs amount is around 2000 for fullHD resolution. Everything else at defaults, and AO disabled. Works perfectly every time.

I did stuff like an animated camera chasing a car moving through a dense CG forest, and it worked very well. I tried even intentionally complex lighting scenarios, but BF+LC just does not flicker, as long as you keep "Use LC for glossy reflections" off and your subdivs amount is high enough.
 
Old 11 November 2013   #6
Hey Rawalanche why for your method does the AO have to be off? I would like to keep it on, what will this affect?

One last thing why does light cache for glossy reflections have to be off?

Brute force is slow as hell to render. I've had to boost my subdivs to 32 to match the quality I was getting from using Irradiance map as primary.
 
Old 11 November 2013   #7
Originally Posted by Rawalanche: Use brute force as primary GI and light cache as secondary one. Make sure you do not use light cache for glossy reflections and that sudbdivs amount is around 2000 for fullHD resolution. Everything else at defaults, and AO disabled. Works perfectly every time.


I agree with Rawalanche. I only ever used these settings for animation and never had to change.

http://predmondvfx.wordpress.com/20...ction-settings/

It depends as said how much resources and time you got as there are other ways.
__________________

 
Old 11 November 2013   #8
Originally Posted by Buzert: Hey Rawalanche why for your method does the AO have to be off? I would like to keep it on, what will this affect?

One last thing why does light cache for glossy reflections have to be off?

Brute force is slow as hell to render. I've had to boost my subdivs to 32 to match the quality I was getting from using Irradiance map as primary.


AO does not need to be OFF, but Brute Force is so accurate for indirect contact shadows, that it makes AO excessive, so only thing AO does then is decrease level of realism you get.

Light Cache for reflections has to be off because if reflections get cached and not raytraced, they will flicker in contact areas.

And it depends on how you optimize your scenes. In scenes with large flat surfaces, IC will probably be always faster, but as soon as any of your lights or objects move, IC will never be flicker-free.

I usually use following settings:
1, start with everything at defaults
2, primary GI brute force, subdivs 20, secondary light cache, subdivs amount same as larger side of rendered output - for example 1280 for 1280x720, or 1920 for 1920x1080
3, Adaptive DMC Min 1, Max 4,
4, Materials with glossiness 0.8-1 will have 8 glossy sudbdivs, materials with glossiness 0.6-0.8 will have 16 glossy subdivs, and materials with glossiness lower than 0.6 will have 24 glossy subdivs. Metal materials with low glossiness sometimes have 32, in cases where they get still noisy
5, subpixel mapping or clamp output is always off
6, always make sure you put your environment map into a full sphere VrayDome light... that light has usually 20-24 light subdivs. Other important lights in the scene usually have 16-20 subdivs, and smaller auxiliary lights have usually 4-8 subdivs.

My rendertimes for FullHD shot with motion blur and GI on average take about 30-60 minutes/frame on i7 2600k kind of machine. Without motion blur, they are usually radically faster.
 
Old 02 February 2014   #9
Can I cheat the baking?

In mental ray I used a little trick when building the rebuild map for Final Gathering. When I was moving the camera around and getting full coverage for the map I would render with the AA extremely low. My render times were much faster. When the map was completely finished being added too then I would put the AA back up.

So can I use the same trick and others when baking the Irradiance map? Will any of the following affect the baking;

Lowering the AA very low
Rendering at a lower resolution
Reducing the glossy subdivisions
Reducing the light subdivisions
 
Old 02 February 2014   #10
I'm still in need of the question right above this post answered but now I have another question.

It seems like Light cache can also have the lighting baked in just like IR. But which mode do I have it set to as I'm moving the camera around?

Progressive path tracing
Single frame
Fly-through

My animation is a fly though and only the camera moves.
 
Old 03 March 2014   #11
Solved

This video answered all my questions.

http://www.youtube.com/watch?v=nkxteEgk-9g
 
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