Brute force Test Very slow :(

[Graceful_Monkey]

Hi,

The Sampler Rate is glowing pretty hot around the trees. Are you using opacity maps on the leaves?

[^Lele^]

I could bet you have issues with your setup, which the IRMap masks, helped by the severe highlight burn in your Rehinard CM.
In between your shader Albedos (call it average brightness) and the lights fixtures, what you are creating is a non-decaying light field, which in turn creates noise (in other engines, it'd be fireflies, in others still it'd be so stupidly clamped you wouldn't notice anyway), which in turn needs samples to be cleaned up.

Mandate number 1 of the "new" method is a settings reset, and *without changing a thing* setting the LC up as instructed.
So do that first, make sure you don't calculate an AO on top of a BF render that way (that was put there a decade ago to hide the mess of the IRMap, it's not only useless, but detrimental to render with BF/LC), stay in LWF (again, Optimised Defaults!), and recalibrate your shaders and lights to match the real world counterparts at best you can: look up light fixture specs, and copy them on your lights,find read albedo tables for material classes (you won't for specific ones!) and try and aim for a diffuse+reflection in the shaders to be in that ballpark, often a *lot* lower than people realise (f.e. most glasses have 7-12% max total reflectivity.).

I'll never tire of saying this: if you depart from LWF, you are very likely to be chasing your own tail.
Not only is LWF the only mathematically correct way to go about it (the radiometric equations expect a linear setup to be able to distribute light properly!), it's also the *only* way to ensure that doing something to your shaders and lights in the max UI will produce *exactly* the expected result (double a light's intensity in the max UI, the rendered intensity will exactly double...).
Any other color mapping setup will result in changes made to lights and shader reflect with a skew on your renders (you bias the solution, in fact, and quite severely so), and so you're left with lights which shine less than they should, and keep raising their intensity for little to no effect, which is then compensated through shaders being brighter, exposure being higher, and contrast, along with a proper light distribution, go out of the window.
To bring back the lost contrast, cue in the 15 years old AO, which made sense before LWF was fleshed out, and per-pixel, multi-sampled, Brute Force solutions were few, not very advanced, and supremely expensive to compute, but should really only be relegated to some obscure post-work, or a data pass of sorts, these days.

TL, DR: Reset your Settings, make sure you stay at the Optimised Defaults the reset provides you with, and reconsider your scene shaders, lights and exposure settings under LWF, before rendering again for final.

[viscorbel]

find read albedo tables for material classes (you won't for specific ones!) and try and aim for a diffuse+reflection in the shaders to be in that ballpark, often a *lot* lower than people realise (f.e. most glasses have 7-12% max total reflectivity.)

Hi Lele, can you explain a bit about what you mean by total reflectivity? Is it diffuse + reflection?
For your glass example, assuming we use black as diffuse and the only reflectivity is specular, this translates to simply using pure white as Reflect color and setting the Fresnel value to 1.72 ~ 2.06, giving us reflection values of 0.07~0.12 at 0 degree incidence angle. It actually seems exactly what most people would use as their settings for glass.

For more complex shaders that actually have a diffuse component, this would mean the basic workflow that goes something like this: find albedo and fresnel ior of said material, then [albedo - specular reflections at 0 deg inc.angle = diffuse value] Adjust diffuse texture to have it's average brightness value match this number (don't forget to correct for srgb gamma)

does that make sense at all?

[Vizioen]

Hi Lele, can you explain a bit about what you mean by total reflectivity? Is it diffuse + reflection?
For your glass example, assuming we use black as diffuse and the only reflectivity is specular, this translates to simply using pure white as Reflect color and setting the Fresnel value to 1.72 ~ 2.06, giving us reflection values of 0.07~0.12 at 0 degree incidence angle. It actually seems exactly what most people would use as their settings for glass.

For more complex shaders that actually have a diffuse component, this would mean the basic workflow that goes something like this: find albedo and fresnel ior of said material, then [albedo - specular reflections at 0 deg inc.angle = diffuse value] Adjust diffuse texture to have it's average brightness value match this number (don't forget to correct for srgb gamma)

does that make sense at all?

This, along with some examples, could clear up a whole lot.

[^Lele^]

It's entirely my fault.

I spent a wee bit of time with hundreds of VRScans, profiling their measured response in RGB in a way which returned the exact albedo value (as Normal fraction, or 0.0-1.0, or %, as you wish to read it) at each incidence angle (more precisely, i sampled it at 10 bit, or 1024 samples across the 90 degree angles), and then we all got lost into other stuff, and I personally never came around to preparing the post.

I'll sync with the VRScans team and see if we have fixes for some old issues in place, and the latest advancements made available, and if not, i'll post some of the usable ones anyway.

As for the reflectance, i speak of the maximum reflectance (so yes, for glass at 90deg.), not the minimum one.
Eyes are often not enough to perceive it (damned, or blessed, be the log-like perception), but reflecting 15% of the sky/sun albedo is a heck of a lot of energy shot back.
When we use higher total reflectance, in the real world, we tend to make the surface rough enough to diffuse it (ie. plaster/paint), or if not, it turns exceedingly shiny (mirrors, and coats, over said glasses!).
Notice that mirrors for massive telescopes approach 95% reflectance (and more if and when they can!), while a house mirror with an aluminium back and a thick-ish glass on it will likely be in the 75% range, partly due to the non-smooth surface at micron-scale (aka: gloss at 0.975 or something. Old mirrors will well diffuse farther objects.), and partly due to the glass absorption.

So, as a general guideline, one should start with very low overall albedos, typically even lower than one would think plausible (white cloth at max 0.6f ? check!), and one will soon find out that going up from a too low albedo is quicker to iterate (faster GI/Caustics!), and much more controlled and pleasant to the eye (too low albedo leads to high contrast, which slowly recedes as one nails the ranges), than doing it the other way around: because of light not extinguishing, and various skews, rendertimes explode, and contrast typically is nowhere to be found, and super hard to retrieve.

Attached, you can see a few of those measurements: X is the angle from view, 0 to 90Deg., Y is the albedo, the curves are conveniently in R, G and B (but may be overlapping in places.); the left Sphere is the "Average Symmetrized" BTF mode used to measure the response, the right one right the full BTF, albeit likely off-scale (as the script didn't adjust the UVs to the sample size, my mistake.), and of course, it goes without saying that the measurement was done properly, no inter-reflections, or coloured light. These renders are for display of the results only.



Notice how the curves are quite characteristics of the type of material response, with a diffuse-like paint displaying darkening at grazing angles, while a coated carpaint will show the expected grazing accentuation of reflectance (to 70% or so!), a White Matte carpaint showing the same-ish behaviour as a wall paint, and a mirror construction can be even inferred from its curves, in this case likely a poor quality, very absorbing glass on top of a poor reflective substrate, to produce said ~75% maximum reflectance, and showing the glass' high absorption, and lack of grazing-angle reflectance, as the view gets shallow.

p.s.: in theory, if you replicated those curves in a falloff map, you'd get identical results (to the left sample!).

[viscorbel]

Can you explain why the scanned data is so different from the refractive index database - for example, here is glass https://refractiveindex.info/?shelf=...y&page=EagleXG
It obviously starts at 4% and goes up to 100% reflectivity at grazing angle, while you are saying that glass has "7-12% max total reflectivity" at 90 degrees !!
Am I misunderstanding something?

Looking at your measurements it seems there is no rule of thumb to use or that good old fresnel workflow is ok only for a handful of materials while most have weird ass curves with darkening /brightening at edges at will :/
I've noticed the darkening of edges on diffuse materials as well, how would we best reproduce this behavior with regular vray material (obviously sending every single material to be scanned is not feasable)
Do you have any workflow suggestions?

[^Lele^]

Can you explain why the scanned data is so different from the refractive index database - for example, here is glass https://refractiveindex.info/?shelf=...y&page=EagleXG
It obviously starts at 4% and goes up to 100% reflectivity at grazing angle, while you are saying that glass has "7-12% max total reflectivity" at 90 degrees !!
Am I misunderstanding something?

https://refractiveindex.info/downloa...splayglass.pdf
Because it's a multi-layer, multi-coated, very specifically designed type of glass (see the comment in my previous post about coats on glasses.).
EDIT:Further, measuring the last 15 to 25 degrees is very often source of noise and bad data (it's hard: if' it's away from you, you don't see it.), and so many of those measurements floating around are interpolated in that area, not exact. Literature on the subject isn't vast, nor simple, as it deals more with photonics and strict physical laws which aren't easy to get around of, in real life, but it's a commonly known issue, difficult to avoid, resolved often only through wishful interpolation.

From that PDF, notice also (very bottom) that even that type of glass, meant to be used as a display substrate, has only 90% or so of the total light passing through (hand on heart who hasn't got white refractive glasses.).

As for usage of correct BTFs in different scenarios, work is being done on making the VRScans (the library already there, and any new addition to it from us) a *lot* more usable in conditions unlike the scanned ones (ie. different color/texture, but same BTF, and so on).
Scanning has been very long, and very expensively, in development precisely because there is no way to principle all materials (cfr. Disney PBS Paper, 2012).
So, no, i have no real suggestions, other than wait it out until the VRScans mature enough (which, hey, it's actually right today, minus some small niggles!).

[Rens]

Can you explain why the scanned data is so different from the refractive index database - for example, here is glass https://refractiveindex.info/?shelf=...y&page=EagleXG
It obviously starts at 4% and goes up to 100% reflectivity at grazing angle, while you are saying that glass has "7-12% max total reflectivity" at 90 degrees !!
Am I misunderstanding something?

Even a standard uncoated simple sheet of glass won't reflect back 4%. That's because the measurement is for the front surface only. The back surface will reflect back light as well leaving less for transmission, it even reflects back close to what the front surface reflects. That's what the archglass shader is for because it gets messy quick especially with coatings and multiple panes.
http://forums.chaosgroup.com/showthr...925#post696925

https://refractiveindex.info/downloa...splayglass.pdf
From that PDF, notice also (very bottom) that even that type of glass, meant to use as a display substrate, has only 90% or so of the total light passing through (hand on heart who hasn't got white refractive glasses.).

Even though yes refraction shouldn't be set to 1.0 white because glass absorbs light as well (giving it its usual greenish tint for example) 100% minus 7-12% reflection = around that 90% transmission already.

[coolhand78]

I could bet you have issues with your setup, which the IRMap masks, helped by the severe highlight burn in your Rehinard CM.
In between your shader Albedos (call it average brightness) and the lights fixtures, what you are creating is a non-decaying light field, which in turn creates noise (in other engines, it'd be fireflies, in others still it'd be so stupidly clamped you wouldn't notice anyway), which in turn needs samples to be cleaned up.

Mandate number 1 of the "new" method is a settings reset, and *without changing a thing* setting the LC up as instructed.
So do that first, make sure you don't calculate an AO on top of a BF render that way (that was put there a decade ago to hide the mess of the IRMap, it's not only useless, but detrimental to render with BF/LC), stay in LWF (again, Optimised Defaults!), and recalibrate your shaders and lights to match the real world counterparts at best you can: look up light fixture specs, and copy them on your lights,find read albedo tables for material classes (you won't for specific ones!) and try and aim for a diffuse+reflection in the shaders to be in that ballpark, often a *lot* lower than people realise (f.e. most glasses have 7-12% max total reflectivity.).

I'll never tire of saying this: if you depart from LWF, you are very likely to be chasing your own tail.
Not only is LWF the only mathematically correct way to go about it (the radiometric equations expect a linear setup to be able to distribute light properly!), it's also the *only* way to ensure that doing something to your shaders and lights in the max UI will produce *exactly* the expected result (double a light's intensity in the max UI, the rendered intensity will exactly double...).
Any other color mapping setup will result in changes made to lights and shader reflect with a skew on your renders (you bias the solution, in fact, and quite severely so), and so you're left with lights which shine less than they should, and keep raising their intensity for little to no effect, which is then compensated through shaders being brighter, exposure being higher, and contrast, along with a proper light distribution, go out of the window.
To bring back the lost contrast, cue in the 15 years old AO, which made sense before LWF was fleshed out, and per-pixel, multi-sampled, Brute Force solutions were few, not very advanced, and supremely expensive to compute, but should really only be relegated to some obscure post-work, or a data pass of sorts, these days.

TL, DR: Reset your Settings, make sure you stay at the Optimised Defaults the reset provides you with, and reconsider your scene shaders, lights and exposure settings under LWF, before rendering again for final.

are you suggesting to just use Linear Multiply Colour Mapping rather than Reinhard?
Is it true that Reinhard at 1.0 & 1.0 (Multiplier & Burn Value) is the same as Linear at the same values?

[viscorbel]

As for usage of correct BTFs in different scenarios, work is being done on making the VRScans (the library already there, and any new addition to it from us) a *lot* more usable in conditions unlike the scanned ones (ie. different color/texture, but same BTF, and so on).
Scanning has been very long, and very expensively, in development precisely because there is no way to principle all materials (cfr. Disney PBS Paper, 2012).
So, no, i have no real suggestions, other than wait it out until the VRScans mature enough (which, hey, it's actually right today, minus some small niggles!).

Ah, thought so. So the future is in the scans.
I'm really glad you mentioned that work is being done to make it possible to change color/texture while keeping the same btf. This is the one thing that imo is essential for them to be usable in my workflow (and I guess many others)

Even a standard uncoated simple sheet of glass won't reflect back 4%. That's because the measurement is for the front surface only. The back surface will reflect back light as well leaving less for transmission, it even reflects back close to what the front surface reflects. That's what the archglass shader is for because it gets messy quick especially with coatings and multiple panes.
http://forums.chaosgroup.com/showthr...925#post696925
Even though yes refraction shouldn't be set to 1.0 white because glass absorbs light as well (giving it its usual greenish tint for example) 100% minus 7-12% reflection = around that 90% transmission already.

Great shader Rens, thanks! I wonder how I missed it :/

[william.morris]

Thanks Lele!

I have read a quite a few of your comments on different threads recently and they have been massively helpful!
I am certainly going to change my approach and settings on new projects from now on.

[^Lele^]

Thanks Lele!

I have read a quite a few of your comments on different threads recently and they have been massively helpful!
I am certainly going to change my approach and settings on new projects from now on.

Let me know how the "conservative" albedo approach works for you!
Also, would you believe in a misguided/rough/ignorantly put sort of way i was rambling about this stuff over ten years ago?
It's still the single thread with the most views in tips and tricks, in fact, and some concepts, once measured with VRScans, turned out to be true (a few more than those proven wrong. i like to think. :P)...
While the video's most definitely dead by now, i think the script works just fine to this day.

http://forums.chaosgroup.com/showthr...t-Bonus-Script!

[Vizioen]

You wouldn't, by any chance, still have those videos

[^Lele^]

fifty bucks.
To cover for the utter shame.
No, really, it's good they're gone. ^^

All i suggested in those long winded things was to QUARTER the overall Albedo of shaders (purely because then the multiplier number in output maps would be 0.255, easy to remember.).
Now, a quarter is likely way, way too much for whites, and possibly too little for some dark tones (with textures on them): I was (admittedly!) eyeballing it hard to illustrate a concept.

It was the early days of Sun, Sky and Physical camera, with exposure, and we were all feeling our way into real-world energy values, out of the old, 8-bit bound, heritage workflow.
Imagine what white 255 surfaces did to scenes, when a sun was thrown into the mix, coupled with fairly unsophisticated BRDF models, a lot less sophisticated sampling routines, and so on...

So, by pure light dimming through darker surfaces, and compensation with the camera exposure, GI would run much much quicker, contrast would be pleasantly high (for back then, remember the context! :P) at a time when most stuff looked fairly flat, out of the box, and that is the whole of the method, in a nutshell.

But i am pleased, chuffed, ecstatic at seeing white matte paint at 0.6 albedo, i tell you!


edit: little bonus, the (now missing) gargoyle render from page 2. No LWF to speak of set up, back then. you may say the thread started the spread of LWF as a concept, since then well refined in today's defaults (between max and v-ray.).

Edit #2: the same scene, but with LWF settings and 3.5 defaults, rendering for the same-ish (23.4 secs for the original, 22.7 for the new) time as the old (hue change due to new sRGB WB in color mapping.).
The old was IRMap plus LC, the new, you know.

[jasonhuang1115]

Thanks so much Lele. Glad I found this thread and hence the 31-page giant thread about this low albedo approach.