K3 - Grass instances

Post your tutorials and help questions in this forum
User avatar
vgabex
Posts: 132
Joined: Sat Dec 09, 2006 2:47 pm
Location: Hungary

K3 - Grass instances

Postby vgabex » Sat Sep 08, 2018 1:13 pm

Hi, I have some problems with an exterior scene.
I'd like to render instanced grass, but the rendertime is incredibly slow compared to the non-instanced version.

With grass instances: 90 minutes
Without grass instances: 21 minutes

Actually the "without instances" version also contains the instanced grass, but it's moved below the ground, so it can't be seen (Y=-575mm instead of the normal -75mm)

What occures the 4.5x rendertime??

Link to scene: https://drive.google.com/file/d/1Nqv_3n6oDxImcP7N8SIAg277lfkpjHqz/view?usp=sharing
Attachments
003_without_grass_00h 21min 12sec.jpg
002_with_grass_01h 30min 47sec.jpg

User avatar
Janusz Biela
Posts: 3988
Joined: Mon Mar 13, 2006 10:39 am
Location: Finland
Contact:

Re: K3 - Grass instances

Postby Janusz Biela » Sat Sep 08, 2018 5:19 pm

This is logic:
- your grass are polygons (hundreds thousands)
- every polygon need to be calculated by GI
- every polygon need to be calculate by Anti Aliasing

Solution:
- use K2 shader with low QMC:
Screenshot 2018-09-08 18.17.13.png
Screenshot 2018-09-08 18.17.13.png (17.63 KiB) Viewed 991 times


You do not need calculate so strong with GI these small objects.
You can use also this for Path Tracing (instead QMC select PT)
Because grass object is very small you will not notice noise from low GI sampling.
Very good system also for carpets.

ideart
Posts: 153
Joined: Mon Nov 16, 2009 4:34 pm

Re: K3 - Grass instances

Postby ideart » Sat Sep 08, 2018 7:46 pm

You will notice horrible noise if you decide to make an animation though.
sotto3d.com

User avatar
Janusz Biela
Posts: 3988
Joined: Mon Mar 13, 2006 10:39 am
Location: Finland
Contact:

Re: K3 - Grass instances

Postby Janusz Biela » Sat Sep 08, 2018 7:57 pm

ideart wrote:You will notice horrible noise if you decide to make an animation though.

Yes

Also I suggest use pure Path Tracing for exteriors.

ideart
Posts: 153
Joined: Mon Nov 16, 2009 4:34 pm

Re: K3 - Grass instances

Postby ideart » Sat Sep 08, 2018 8:07 pm

So how can noise in grass be avoided in animations?
Because it is there also in photon map.
sotto3d.com

User avatar
Janusz Biela
Posts: 3988
Joined: Mon Mar 13, 2006 10:39 am
Location: Finland
Contact:

Re: K3 - Grass instances

Postby Janusz Biela » Sat Sep 08, 2018 9:44 pm

You can not. Objects are so small that AA will have always problem position correct pixels - even if you use FSAA G10.
This is no problem with noise so much but more with AA pixels blending positioning.
Better is when you render at least FullHD and later use de-noiser under After Effect. Also Motion blur can reduce bad effect.
We do not have yet Motion Blur Buffer (is on the list) so you have to use build in AE. Is not perfect especially with small objects (twisted effect).
For far view better is use only texture.
You can use ID map for blurring grass region under AE (ground ID, not grass ID).

To speed up this problematic regions I need to talk with G. about "z-buffer Global Illumination" - the idea is that to use distance for reducing GI samples so grass which is far will have very poor GI solution....it will be not visible bad effect because far small objects are in one pixel of image and is no need to render GI per object but better GI per pixel.
I will talk with G. about this forever running problem - he always has inventive ideas.

artattak
Posts: 288
Joined: Thu May 26, 2011 6:23 pm

Re: K3 - Grass instances

Postby artattak » Thu Nov 15, 2018 4:21 pm

the grass looks great.

But it has to be optimized for animation.
Reduce polygons and parameters of surfacles.
In the dublesidet settings, the lower part of the grass can be switched off for reflection.
In animation, video compression plus the effects of postprocess dof, motion blur chromic aberation, mask noise and minor imperfections.
In the real movie, you can not see individual blades of grass.


Return to “Help and Tutorials”

Who is online

Users browsing this forum: No registered users and 2 guests