No result while rendering without ambient

Use this forum for general user support and related questions.
lighting_freak
Posts: 76
Joined: Thu Jan 18, 2018 6:02 pm

No result while rendering without ambient

Post by lighting_freak » Thu Feb 15, 2018 7:48 pm

Hi,

I have the same rendering in two conditions.
I'm focused on the lit appearance of the LED-chips.

One condition is using a dark ambient HEMI source additionally and creates a result image.
OSRAM-MULTILED_LTRB_GFSF_with_ambient.zip
(1.59 MiB) Downloaded 18 times
The other only contains only the chip sources and the results remain black.
OSRAM-MULTILED_LTRB_GFSF_no_ambient.zip
(1.59 MiB) Downloaded 19 times
This texture is propably missing.
Leiterplatte.jpg
This is my result (this test using volume scattering)
LED.jpg
BR
OS - Windows 7 X64
CPU - Intel CORE i7
GPU1 - Variants of notebook card from nVidia
GPU2 - Variants of notebook onboard card from Intel
Lux - Latest possible relaease

User avatar
B.Y.O.B.
Developer
Posts: 1466
Joined: Mon Dec 04, 2017 10:08 pm
Location: Germany
Contact:

Re: No result while rendering without ambient

Post by B.Y.O.B. » Thu Feb 15, 2018 8:32 pm

When I change the unit scale to 1 it seems to work.
Probably some matrix is not getting scaled by unit scale, I'll investigate.

Opened issue: https://github.com/LuxCoreRender/BlendLuxCore/issues/77
Support LuxCoreRender project with salts and bounties

neo2068
Developer
Posts: 85
Joined: Tue Dec 05, 2017 6:06 pm

Re: No result while rendering without ambient

Post by neo2068 » Sun Feb 25, 2018 9:55 am

When I raise the gain of the LED Emission from 1 to 10, it works for me. The luminous flux (gain*power*efficacy) of the lights in the original .blend file is <=1 lm. Is that a problem for the renderer? The problem only occurs with BiDir renderer.

One remark, you shouldn't use multiple scattering for the world volume. It is very slow and single scattering should be sufficient.
i7 5820K, 32 GB RAM, NVIDIA Geforce GTX 1080 + GTX 780, Windows 10 64bit, Blender 2.79b
Support LuxCoreRender project with salts and bounties

lighting_freak
Posts: 76
Joined: Thu Jan 18, 2018 6:02 pm

Re: No result while rendering without ambient

Post by lighting_freak » Mon Feb 26, 2018 10:26 pm

Hi,

Those luminous fluxes that I've used are real world values. Especially for this LED type are neither very high not pretty low.

In order to compute physical correct (even in luminance values) images it would be great to make it possible to handle those fluxes.

By the way, why don't you get rid of the gain, efficiacy ,watt input and just use lumens?

BR
OS - Windows 7 X64
CPU - Intel CORE i7
GPU1 - Variants of notebook card from nVidia
GPU2 - Variants of notebook onboard card from Intel
Lux - Latest possible relaease

User avatar
B.Y.O.B.
Developer
Posts: 1466
Joined: Mon Dec 04, 2017 10:08 pm
Location: Germany
Contact:

Re: No result while rendering without ambient

Post by B.Y.O.B. » Fri Mar 02, 2018 2:54 pm

neo2068 wrote:
Sun Feb 25, 2018 9:55 am
When I raise the gain of the LED Emission from 1 to 10, it works for me. The luminous flux (gain*power*efficacy) of the lights in the original .blend file is <=1 lm. Is that a problem for the renderer? The problem only occurs with BiDir renderer.
Seems related to this problem, maybe the same: viewtopic.php?f=4&t=87#p1475
I think because the scene is so small there is very little emitted light, until we run into floating point precision issues.

I think part of the problem is how we export the unit scale.
We scale all objects in the scene by the scene scale (like it was done in LuxBlend).
I think the point of the scene scale is to get rid of precision issues with very small/large objects, not to create new issues.
My guess is that we should change our approach: do not scale all the objects in the scene, but instead scale all other parameters that depend on scene scale (volume absorption depth, camera fstop etc.).
What do you think?
Support LuxCoreRender project with salts and bounties

lighting_freak
Posts: 76
Joined: Thu Jan 18, 2018 6:02 pm

Re: No result while rendering without ambient

Post by lighting_freak » Mon Mar 05, 2018 10:07 pm

Hi,

that's a challanging question you were asking.
Some time ago there was guy called B.Y.O.B. in a Blender forum who pointed me to lux render. The open question in that forum was dealing about shaders and physics based volume description. His Mantra was "keep an eye on the dimensions of your scene"...

Well, for me I'm very used to work in mm scale that's why I was happy to find the unit scale option in "Blender" and also the preset of mm was very welcome to my engineers soul. Will it be better if I get used to maybe a meter-preset?

In classic lux I needed to learn that I have to scale all my volume definitions with factor 1000 to make lux calculating correct results.
How will it help to scale the change the scaling type?

BR
OS - Windows 7 X64
CPU - Intel CORE i7
GPU1 - Variants of notebook card from nVidia
GPU2 - Variants of notebook onboard card from Intel
Lux - Latest possible relaease

User avatar
B.Y.O.B.
Developer
Posts: 1466
Joined: Mon Dec 04, 2017 10:08 pm
Location: Germany
Contact:

Re: No result while rendering without ambient

Post by B.Y.O.B. » Tue Mar 06, 2018 7:25 am

The thing is, in an ideal world with infinite floating-point precision, everyone would say "1.0 = 1 meter" and call it a day.
But unfortunately, if you say 1.0 = 1 meter and you make things very small (like in your scene) or very big, you run into problems with floating point precision very fast.
That's why there's the unit scale factor in Blender (at least I assume it was implemented because of this).
It let's you change the 1.0 = 1 meter rule to, for example, "1.0 = 1cm" for very small scenes. So you can still have very small objects, but internally the floating point precision does not suffer.

However, a changed unit scale affects many materials (bump map height), volumes (absorption), camera (fstop, depth of field).
So I guess this was the reason why the LuxBlend developers back in the day said "we'll stick to 1.0 = 1 meter and scale all objects in the scene by Blender's unit scale".
However this re-introduces the floating point issues, which we see in your example scene.

So now my idea was to scale all the other effects I listed above instead of the objects in the scene.
Inherently, floating point numbers don't have a scale of course, it's a relative thing if you interpret 1.0 as 1 meter or 1 cm or whatever.
Support LuxCoreRender project with salts and bounties

lighting_freak
Posts: 76
Joined: Thu Jan 18, 2018 6:02 pm

Re: No result while rendering without ambient

Post by lighting_freak » Tue Mar 06, 2018 5:51 pm

Hi,

Do you see a chance to predtermine whether a scribe will run into such a precision issue? How does other ray tracing solutions manage this problem?

I think the old lux doesn't show that issue with the same scene or object. I've rendered lot of images using such an LED body and such an chip size with those luminous fluxes.

Anyway let's test the turn around scaling. Is there anything I can do to support your investigations on that (beside learning how to write programs)

BR
OS - Windows 7 X64
CPU - Intel CORE i7
GPU1 - Variants of notebook card from nVidia
GPU2 - Variants of notebook onboard card from Intel
Lux - Latest possible relaease

User avatar
B.Y.O.B.
Developer
Posts: 1466
Joined: Mon Dec 04, 2017 10:08 pm
Location: Germany
Contact:

Re: No result while rendering without ambient

Post by B.Y.O.B. » Tue Mar 06, 2018 5:57 pm

In 3ds max there's a window that shows the floating point accuracy:

Image

But I don't think there's something like this in Blender.
Support LuxCoreRender project with salts and bounties

User avatar
Dade
Developer
Posts: 1237
Joined: Mon Dec 04, 2017 8:36 pm

Re: No result while rendering without ambient

Post by Dade » Tue Mar 06, 2018 6:02 pm

B.Y.O.B. wrote:
Tue Mar 06, 2018 5:57 pm
In 3ds max there's a window that shows the floating point accuracy:

Image

But I don't think there's something like this in Blender.
There is some web page around showing similar stuff, something like https://www.h-schmidt.net/FloatConverter/IEEE754.html
Support LuxCoreRender project with salts and bounties

Post Reply