Author Topic: dubcats secret little hideout  (Read 92617 times)

2018-01-31, 10:29:55
Reply #135

Juraj Talcik

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OSL doesn't have access to BRDF though so I am not sure if we would get anything else than the values translated to CoronaMTL internally.
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2018-01-31, 11:25:22
Reply #136

Fluss

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OSL doesn't have access to BRDF though so I am not sure if we would get anything else than the values translated to CoronaMTL internally.

Just checked, you're right OSL does not allow to write custom BRDF / can only use what's available... That's sucks! So we have to wait for a proper 'state of the art' BSDF.

I was so optimistic ! Juraj you just ruined my day :)

2018-02-01, 09:04:18
Reply #137

Fluss

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dubcat, can you share your scene pls ? I'd like to make some direct comparison with Vray alshader.





2018-02-01, 16:43:24
Reply #138

dubcat

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We are definitely on to something here.

Glad you like it. :)

Thanks A LOT Dubcat

Thank you :)

Is your Megascans export script still available, Dubcat? The link in your Megascans thread 404s :(

I've been working on new scripts for Quixel since last winter.
The new scripts use my "Specular to IOR v2" LUT to auto convert specular maps, and they read the proper displacement height value from the json file.
I don't have a release date, but it will be worth the wait!

I'll make a new post here to inform you guys when it's released.

dubcat, can you share your scene pls ?

That scene is long gone, but I've made a new one for you. The zip contains a "Corona Sky" HDRi for consistent lighting and an fbx with geo/camera.
I had to use an external file sharing service, because the forum cap is at 30mb.

https://www.sharebase.net/58ed6f5e1e79212f



Hope I didn't miss any questions, if so, let me know.

edit:
I forgot to mention that Epic has fixed the blue light problem in Unreal.



edit edit:
Here is the ACES tonemapper if anyone is interested.

https://www.desmos.com/calculator/h8rbdpawxj

If you look at the numbers on the left side of each column, these are the parameters.

4   - Slope        - 0.88
7   - Toe           - 0.55
8   - Black Clip  - 0
11 - Shoulder   - 0.26
12 - White Clip - 0.04
« Last Edit: 2018-02-02, 03:47:00 by dubcat »
             ___
    _] [__|OO|
   (____|___|     https://www.twitch.tv/dubca7 / https://soundcloud.com/dubca7 / https://dubcatshideout.com  ( ͡° ͜ʖ ͡°)

2018-02-03, 12:45:55
Reply #139

Fluss

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Thanks dubcat for the scene. I'll make some comparison with shaders that support diffuse roughness
« Last Edit: 2018-02-03, 16:45:13 by Fluss »

2018-02-04, 12:58:56
Reply #140

Fluss

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I've finally made some test on the diffuse shading. Indeed, Corona seems to use pure Lambertian diffuse shading model which is suitable to describe high glossiness materials. When it comes to rougher materials, the oren-nayar model is more suitable.

example :



Arnold and redshift both use the oren-nayar diffuse shading model and then, expose a diffuse roughness parameter.

When diffuse roughness is set to 0, then it's pure Lambertian. As far as this value is changed, it switches to the Oren-Nayar implementation. You can see examples below (don't mind the little exposure difference between renderers, I matched them by eye, really quickly).

I did not find a Fstorm demo installation but from what I've seen from dubcat's tests, the Fstorm diffuse shading model seems quite off compared to other solutions. Don't know what algorithm is used there. Also noticed some strange artifacts on the sphere highlight in arnold when using strong roughness values. Redshift implementation seems to be the more consistent one.

Vray's diffuse roughness is completely off and I now understand why nobody (including me) uses it...

Also, to clarify things, diffuse roughness is not the same as glossy roughness. Most materials cap around 0.3 and shouldn't go over 0.5. From what I've found over the web, some artist tends to use a basic rule to get reliable results: diffuse roughness = glossy roughness * 0.33. There is something to dig in here.

It would be really nice to get diffuse roughness and glossy fresnel to be part of corona in the near future! Please!


2018-02-04, 15:07:39
Reply #141

Fluss

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one more test, Redshift , Lambertian vs Oren-Nayar diffuse shading :

Glossy roughness @0.7 - Diffuse Roughness @0.0

Glossy roughness @0.7 - Diffuse Roughness @0.23 -> 0.7*0.33 as explained above

Glossy roughness @1.0 - Diffuse Roughness @0.0

Glossy roughness @1.0 - Diffuse Roughness @0.33
« Last Edit: 2018-02-04, 16:28:02 by Fluss »

2018-02-05, 09:56:59
Reply #142

Juraj Talcik

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F-Storm does almost 100perc. use Oren-Nayar diffuse shading, or some in-house but nonetheless based on it (like their copy of GGX).

The most interesting approach is what the Disney guys (Brent) have done. They manually fitted the model so that rough materials have some retroreflection.

I generally like what they do (test and see when it matches reality) instead of just adding code and ending up with unrealistic crap. Lambert has to go.
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2018-02-05, 10:06:10
Reply #143

pokoy

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A few users were asking for Oren-Nayar on a regular basis, probably too few to be heard. It's really needed for a lot of surfaces, I'd be really happy if we got an improved shading model.

Thanks for the test images - from all the tests, Redshift's version looks best to me. Kind of surprising since I find many of their gallery images to look quite artificial, I always thought their shading model isn't as nice as Corona's.

2018-02-05, 10:44:10
Reply #144

Juraj Talcik

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Redshift still suffers from this odd reputation because their early user-base didn't focus on photorealistic work that much.

But their 2nd version came with state-of-art PBR shader with multiple brdf selection in 1/10 fraction of the time it took Corona to even fix GGX halo ;- ).
It was basically flawless, perfection.
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2018-02-05, 11:42:33
Reply #145

Fluss

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The most interesting approach is what the Disney guys (Brent) have done. They manually fitted the model so that rough materials have some retroreflection.

I generally like what they do (test and see when it matches reality) instead of just adding code and ending up with unrealistic crap. Lambert has to go.

I've also read the disney paper, the approach is indeed quite interesting. The only thing that bother me in this shader is the specular control which stands in lieu of an explicit index-of-refraction. Except that, it looks like a fantastic shader to work with. Renderman is Full-featured and free for non-commercial use, just need to grab a demo version of maya to test that out.

I finally managed to test Fstorm and I have to say that I'm quite impressed! Everything feels so natural, and not only on the diffuse part, glossy fresnel is a no brainer here! I'll dig into it a bit further.

F-Storm does almost 100perc. use Oren-Nayar diffuse shading

I'm not sure about that. It's default 0.8 and seems to be "Lambertian-like" at 0.99. It's also capped to 0.5. What's more, transition between light and shadows is tremendously softer.


A few users were asking for Oren-Nayar on a regular basis, probably too few to be heard. It's really needed for a lot of surfaces, I'd be really happy if we got an improved shading model.

Thanks for the test images - from all the tests, Redshift's version looks best to me. Kind of surprising since I find many of their gallery images to look quite artificial, I always thought their shading model isn't as nice as Corona's.

A better diffuse model is highly needed to get rid of that rough surface plastic look.

After some more tests, I'm a bit skeptical about redshift's implementation as it's quite noticeable in the highlighted parts but it does almost nothing in the shadows. Arnold looks weird on extreme values but it also significantly changes the diffuse appearance in the shadows which looks more convincing to my eye. It's more noticeable on the happy Buddha, I'll post some more experiments later.

2018-02-05, 14:04:11
Reply #146

Fluss

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Juraj, can you PM me ? I'd like to discuss some stuff with you if you don't mind

2018-02-05, 15:24:56
Reply #147

nkilar

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Juraj, can you PM me ? I'd like to discuss some stuff with you if you don't mind

I'm a lurker here (without much to say) and I really appreciate you guys going at it - going at the problem that is. :) That said, the more public spamming you guys do the better - I really enjoy reading the findings you smart people come up with. Hurrah! Thank you!

2018-02-05, 23:47:08
Reply #148

oddvisionary

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Juraj Talcik : F-storm + their? No, it's just one guy haha.
Freelance Post-Prod / Lighting & Look Dev 3D Generalist | VFX Designer | Sound Effect Recordist & Sound Designer

Corona Discord server : https://discord.gg/2uxq8EA

2018-02-06, 10:39:23
Reply #149

Juraj Talcik

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Yeah I also prefer to bounce opinions public :- ). That's what threads like this are for. Don't worry the devs are not that sensitive and need some push :- )

But if it's something reeally private like just use my old mail juraj(dot)talcik (at) yahoo (com).
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