Puzzling Object Color Shift Outside vs Inside the Glass Cube & Seen Thru It Even When IOR at 1 and Reflection at 0,0,0

Use this forum for general user support and related questions.
Forum rules
Please upload a testscene that allows developers to reproduce the problem, and attach some images.
Post Reply
Jan
Posts: 37
Joined: Sun Jan 10, 2021 2:37 pm

Puzzling Object Color Shift Outside vs Inside the Glass Cube & Seen Thru It Even When IOR at 1 and Reflection at 0,0,0

Post by Jan »

back of glsss SOLID.jpg
back of the glass RENDERED.jpg
emissive rectangular plane positioned just 0.1" outside and from the back surface of the 2" thick glass cube and viewed frontally through it


inside glass SOLID.jpg
inside glass RENDERED.jpg
emissive rectangular plane moved 0.1 inch inside the back surface of the glass cube and viewed frontally through it

Already eliminated glass light reflections by setting IOR to 1 and same as vacuum as well no other light sources present except the glass transmittance color not equal to 1,1,1. However with transmittance color at 1,1,1 there are no color shift.

What else would cause this strange color shift???


Please see attached blender file
glass properties.blend
(2.23 MiB) Downloaded 120 times
User avatar
Dade
Developer
Developer
Posts: 5672
Joined: Mon Dec 04, 2017 8:36 pm
Location: Italy

Re: Puzzling Object Color Shift Outside vs Inside the Glass Cube & Seen Thru It Even When IOR at 1 and Reflection at 0,0

Post by Dade »

Jan wrote: Sat Mar 20, 2021 2:04 pm What else would cause this strange color shift???
Have you set the inside/outside volume of the objects ? This kind of problems are usually related to not having a correct volume setup.

LuxCore doesn't know if a ray starting from camera or light sources is inside a volume so it uses the information of the first hit surface (i.e. its inside/outside volume definition).
You can easily end with strange asymmetrical behavior if you don't define all inside/outside object volumes when you move the camera or a light source inside/outside of an object.
Support LuxCoreRender project with salts and bounties
Jan
Posts: 37
Joined: Sun Jan 10, 2021 2:37 pm

Re: Puzzling Object Color Shift Outside vs Inside the Glass Cube & Seen Thru It Even When IOR at 1 and Reflection at 0,0

Post by Jan »

Dade wrote: Sun Mar 21, 2021 10:58 am
Jan wrote: Sat Mar 20, 2021 2:04 pm What else would cause this strange color shift???
Have you set the inside/outside volume of the objects ? This kind of problems are usually related to not having a correct volume setup.

LuxCore doesn't know if a ray starting from camera or light sources is inside a volume so it uses the information of the first hit surface (i.e. its inside/outside volume definition).
You can easily end with strange asymmetrical behavior if you don't define all inside/outside object volumes when you move the camera or a light source inside/outside of an object.
Hi, I tried again but the outcome is still the same.
GLASS CUBE SOLID.jpg
COMPARISON.jpg
GLASS SHADER.jpg
inner volume and outer volume of the glass cube both defined. IORs set to 1

PLANE_SHADER.jpg
outer volume also of the luminance emission plane defined. IOR set also to 1


With all the materials volume IOR all the same and set at 1 as well Absorption Color 0,0,0 to eliminate loses due to absorption, refractions, reflections and scattering etc. except for the Glass Material Transmission Color 1, 0.829707, 0.614009 but still the right side glass cube looks inexplicably darker?
Attachments
glass properties 2.blend
(2.23 MiB) Downloaded 116 times
User avatar
Dade
Developer
Developer
Posts: 5672
Joined: Mon Dec 04, 2017 8:36 pm
Location: Italy

Re: Puzzling Object Color Shift Outside vs Inside the Glass Cube & Seen Thru It Even When IOR at 1 and Reflection at 0,0

Post by Dade »

You are setting your glass transmission to "1 0.829707 0.614009", so it is applied 2 times in one case (i.e. entering/exiting the glass) and only one (i.e. only entering the glass) on the other. If you set the value to "1 1 1" , you will get the same rendering in both cases.

Materials are a "surface" attribute while volumes are about the "space" inside an object. I guess you want to use volume transmission parameter instead of surface transmission.
Support LuxCoreRender project with salts and bounties
Jan
Posts: 37
Joined: Sun Jan 10, 2021 2:37 pm

Re: Puzzling Object Color Shift Outside vs Inside the Glass Cube & Seen Thru It Even When IOR at 1 and Reflection at 0,0

Post by Jan »

Updates:

I finally got the expected results by setting the Glass Internal Volume Absorption Color to the Desired Color while the Absorption Depth to the Thickness of the Glass Cube while the Glass Material Transmission Color now to 1,1,1 instead. Material Transmission Color doesn't account for the material thickness and was twice filtered in case when the emissive plane is at the back side of the glass cube.

However I got another issue. The color looks only perfectly even when viewed orthographically .

orthographic and front
orthographic.jpg


perspective and front
perspective.jpg

perspective and angled
perpectively and slanted.jpg

Where did the white come from? Why the color changes seems to be so abrupt?
Attachments
glass properties 2 revised.blend
(2.23 MiB) Downloaded 113 times
Last edited by Jan on Mon Mar 22, 2021 11:44 am, edited 3 times in total.
Jan
Posts: 37
Joined: Sun Jan 10, 2021 2:37 pm

Re: Puzzling Object Color Shift Outside vs Inside the Glass Cube & Seen Thru It Even When IOR at 1 and Reflection at 0,0

Post by Jan »

Dade wrote: Mon Mar 22, 2021 10:55 am You are setting your glass transmission to "1 0.829707 0.614009", so it is applied 2 times in one case (i.e. entering/exiting the glass) and only one (i.e. only entering the glass) on the other. If you set the value to "1 1 1" , you will get the same rendering in both cases.

Materials are a "surface" attribute while volumes are about the "space" inside an object. I guess you want to use volume transmission parameter instead of surface transmission.
Thanks!
Volume Transmission parameter you mean Absorption Color and Absorption Depth?
I have another issue when using Absorption Color and Absorption Depth please check the post above this post. :P
User avatar
Dade
Developer
Developer
Posts: 5672
Joined: Mon Dec 04, 2017 8:36 pm
Location: Italy

Re: Puzzling Object Color Shift Outside vs Inside the Glass Cube & Seen Thru It Even When IOR at 1 and Reflection at 0,0

Post by Dade »

Jan wrote: Mon Mar 22, 2021 11:28 am However I got another issue. The color looks only perfectly even when viewed orthographically .
It is correct :?: With orthographic camera, the rays will travel inside the cube for the same distance (i.e. they are all parallels) while, with perspective camera, the rays will travel inside for different distances (i.e. they irradiate from the camera origin, in different directions), more they travel and more they are absorbed.
Support LuxCoreRender project with salts and bounties
Jan
Posts: 37
Joined: Sun Jan 10, 2021 2:37 pm

Re: Puzzling Object Color Shift Outside vs Inside the Glass Cube & Seen Thru It Even When IOR at 1 and Reflection at 0,0

Post by Jan »

Dade wrote: Mon Mar 22, 2021 12:58 pm
Jan wrote: Mon Mar 22, 2021 11:28 am However I got another issue. The color looks only perfectly even when viewed orthographically .
It is correct :?: With orthographic camera, the rays will travel inside the cube for the same distance (i.e. they are all parallels) while, with perspective camera, the rays will travel inside for different distances (i.e. they irradiate from the camera origin, in different directions), more they travel and more they are absorbed.
Thanks and agreed! Additionally it must be the different Absorption Depth that affects the Luminances of the surface at different angles from the camera origin and the further the angle from the camera origin to the surface area portion the darker it should look for perspective projection.

Emission Plane Only Perspective Angled.jpg
This is not the case for Lambertian emission surfaces without the glass panel between the camera.


perpectively and slanted_sRGB_Filmicjpg.jpg
It looks more natural now with Filmic View Transform under Color Management :D
Post Reply