Visible difference between GPU and CPU renders

General questions about Indigo, the scene format, rendering etc...
Post Reply
6 posts • Page 1 of 1
User avatar
Headroom
Indigo 100
Posts: 1058
Joined: Wed Aug 08, 2007 1:07 pm
Location: Spartanburg, SC, USA
Contact:

Visible difference between GPU and CPU renders

Post by Headroom » Sat Jul 13, 2019 10:47 am

I rendered this simple test scene to see how GPU Pathtracing would compare to CPU rendering, BIDIR MLT in this case.
My interest was mainly to see evaluate difference between dispersion and caustics.

Both images rendered for 40 minutes.the light source is a HDRI with many small light sources and the material of the twisted ring is the Lead Crystal from the online material DB with couchy B enabled.
The GPU renderer is nobly cleaner and the caustics are clearly visible. Nice!

However, there are dark areas mostly visible in the GPU render in in the left part of the image in the outer edges of the twisted torus. Those are not present in the CPU render. I checked the other CPU render modes as well (just not for 40 minutes) and these dark areas are not present in those render modes either..

Thoughts ?
Attachments
Twist_torus.Scene_circus40minbidirmlt.jpg
BIDIR MLT
Twist_torus.Scene_circus40minpathGPU.jpg
Path GPU

User avatar
contegufo
Posts: 522
Joined: Tue Aug 11, 2015 8:41 am
Location: Lucca ITALY

Re: Visible difference between GPU and CPU renders

Post by contegufo » Sat Jul 13, 2019 7:49 pm

Hi

the second image is the best overall; which gpu did you use?
Mac Mini 2011 - 2,3 GHz Intel Core i5
16 GB 1333 MHz DDR3 - Intel HD Graphics 3000 512 Mb.
Samsung SSD 860 EVO 500GB - MacOS High Sierra 10.13.6



https://www.behance.net/Paolo_Conti

User avatar
fused
Developer
Posts: 3648
Joined: Fri Sep 22, 2006 7:19 am
Location: Berlin, Germany
3D Software: Cinema 4D

Re: Visible difference between GPU and CPU renders

Post by fused » Sat Jul 13, 2019 8:43 pm

By default the GPU pathtracer uses a path depth of 8. It can lead to darkeing in certain areas, especially with specular materials. You can turn up the depth and the dark spots should get lighter or disappear completely (but it will also render a little slower).

User avatar
Headroom
Indigo 100
Posts: 1058
Joined: Wed Aug 08, 2007 1:07 pm
Location: Spartanburg, SC, USA
Contact:

Re: Visible difference between GPU and CPU renders

Post by Headroom » Sat Jul 13, 2019 11:53 pm

@fused
Thanks for the tip. increasing Path Depth does indeed eliminate these dark areas. it's just not a setting available in the Blendigo UI (or I simply have to look harder ):

@Contefugo:
All of these images have rendered for 40 minutes on a 2017 MacBook Pro with a Radeon Pro 560.
This is not usually how long you want to wait for a GPU render, but these serve as experiments for me to determine the best render set up for my situation. At this time I think I'll invest in a eGPU to complement my notebook.
Twist_torus.Scene_circus40minpathGPU_pathdepth16.jpg
GPU Path depth 16
Twist_torus.Scene_circus40minpathGPU_pathdepth24.jpg
GPU Path depth 24

User avatar
pixie
Indigo 100
Posts: 2332
Joined: Sat Dec 29, 2007 4:54 am
Location: Away from paradise
3D Software: Cinema 4D
Contact:

Re: Visible difference between GPU and CPU renders

Post by pixie » Sun Jul 14, 2019 12:14 am

Well, the thing is, specular materials and caustics always tend to take a lot more to denoise then simpler materials.

User avatar
Zalevskiy
Posts: 250
Joined: Thu Jul 16, 2015 12:36 am
Location: Mars
3D Software: Blender

Re: Visible difference between GPU and CPU renders

Post by Zalevskiy » Sun Jul 14, 2019 2:56 am

wow I just found out about this option, why not add to faq? to make new indigo users understand

popular render engines have video instructions, this will all help make friends with this wonderful render engine

Post Reply
6 posts • Page 1 of 1

Who is online

Users browsing this forum: No registered users and 31 guests