Corona- Surface details and glosiness??

[melviso]

I have been reading up a lot on surface details and how that affects how glossy/blurry reflections become including brushed surfaces. I decided to experiment by using only bump or displacement maps to influence how blurry reflections can become but I have noticed I still need to enter a value in the glossiness to get the desired effect. I am guessing the bump/displacement details are not tiny or fine grain enough or Corona only renders with glossiness parameters specified?

EDIT: Seems a glosiness map or surface roughness map is required to get the end result. Seems bump maps cannot be used to specify surface roughness or glossiness using Corona.

[juang3d]

Why would you like to modify glossiness using bump when you have a glossiness slot?

In reality the glossiness is provoked byt the surface imperfections, so if we have a perfectly polished surface with have a clear reflection, if we have a completely chaotic and imperfect surface we have no clear reflection, but in 3D things are simulated, so while you can modify the reflection using bump, of course, you won't get the same effect as using glossiness because it is a simulation, so surface imperfection won't give you the "correct" result just by itself, the actual bump it's a simulation also, so it won't behave as real surface imperfection.

This is how I understand all this, maybe i'm wrong in anything, if it's so please devs correct me!

Cheers.

[Juraj]

Well it comes more to the fact that bumpmap just doesn't simulate that kind of microscopic detail that would affect the roughness but his concept isn't wrong in theory. But in practice it won't work correctly for most renderers :- )

{for example CryEngine integrated very different kind of PBR compared to Unreal4/Disney, and paired roughness map to normal map (it resides in alpha channel and thus shares same resolution and detail)}

Bump is best kept to "small" detail, like 1-2mm, beyond that it's normal map/displace and bellow glossiness slot.

[juang3d]

Great explanation Juraj :D

BTW this thread should go in the help forum I think :)

Cheers.

[melviso]

Well it comes more to the fact that bumpmap just doesn't simulate that kind of microscopic detail that would affect the roughness but his concept isn't wrong in theory. But in practice it won't work correctly for most renderers :- )

{for example CryEngine integrated very different kind of PBR compared to Unreal4/Disney, and paired roughness map to normal map (it resides in alpha channel and thus shares same resolution and detail)}

Bump is best kept to "small" detail, like 1-2mm, beyond that it's normal map/displace and bellow glossiness slot.

Interesting, Juraj, So how far would u go using normal map against displacement map for detailing. I did notice Corona doesn't render glosiness with respect to displacement map as well. Guess thats what glossiness and reflection maps are for since its not like the real world but I do feel reflection and glosiness as well as bump/normal should be tied to one map that defines the surface roughness. That would make materials more similar to the real world.

 Once u can get ur materials surface right, the rest should be easy to set up. I am still trying to figure out what makes a material reflective or not. Its defintely not the surface roughness but the amount of light it reflects back. But I am guessing if a material is very smooth on a microscopic level it reflects more light compared to cotton which is very rough so it absorbs more light rather than reflect??

[Juraj]

Not completely, rough surface 'scatters' light instead of reflecting it back in specular direction, up to point where it's pure diffuse reflection (completely rough-matt surface---)lambertian shader).

But effectively in rendering unless the shading model is built to rely completely on 'roughness' parameter it just doesn't behave....that well. So what you do, in Corona (or similar renderers) you manually lower the reflection the rougher (lower glossiness) it is,
but you can't do it sufficiently through bump/normal/disp.

In practical terms I use it like this:

Micro-level= Only Glossiness slot, for metals, I even rarely use bumps, and when I do, it's just for heavier scratches, not the tiny fractures.
1-2mm= Bump map---) Carpets,Fabrics,etc.. Some of these materials are so rough that their specular component is like non-existent so you might as well simulate it purely through 0 reflection and only diffuse with fallof for some self-shading.
1-10mm=Normal map---)Foliage, rocks,etc... Basically when it is impractical (like always...) to use displacement, but I still want 3D/Relief feel for reflection. It basically just alters the appearance of the large part of geometry, you still have to use glossiness/reflection to set your specularity.
1cm+ = Displacement---) For whatever else.

Each of them can simulate roughness slightly to some point but that microdetail is mostly filtered away so the concept doesn't work that way.

[melviso]

hanks for sharing some of ur knowledge. just checked out ur portfolio work.They are very very good. Hope u wouldn't mind if I ask u some technical questions from time to time.
I think I would be using normal maps from now on.I noticed ur fabrics look very rough texturewise. So u use a fall off node with a darker and lighter version of the same texture for the diffuse slot?

[Juraj]

Thanks for sharing some of ur knowledge. just checked out ur portfolio work.They are very very good. Hope u wouldn't mind if I ask u some technical questions from time to time.
I think I would be using normal maps from now on.I noticed ur fabrics look very rough texturewise. So u use a fall off node with a darker and lighter version of the same texture for the diffuse slot?

Yes. I plan to show tutorial on describing the various curves you can use on that but I don't have time right now, and I need to finish big project but after that I'll get to it.

[melviso]

Noted. Looking forward to it. Thanks for the pointers.I am thinking of just using only normal maps even for tiny details and ditching bumps all together.Displacements maps makes sense the way u use them. Will start using this in my workflow.

[melviso]

I have been reading more about glossy maps and I need some explanation about it. From what I understand glossy maps are used to simulate surface roughness. I am now finding out it has to do with the width of the specular highlight/reflection map. Black means the width is wider while white means the highlight will be tighter.So say u have a monochrome noise map with high contrast of black and white, how does that work? i am supposing white areas mean glossy and black areas clear reflections or  white areas will have pointy/tighter highlights while grey or darker areas will have broader highlights? I am thinking the latter is the more accurate one while u specify in the corona material the glossiness using the parameter between 0-1?

Or does this center on the range between black and white pixels in the map and that determines whether a surface is glossy or not.

[romullus]

I have been reading more about glossy maps and I need some explanation about it. From what I understand glossy maps are used to simulate surface roughness. I am now finding out it has to do with the width of the specular highlight/reflection map. Black means the width is wider while white means the highlight will be tighter.So say u have a monochrome noise map with high contrast of black and white, how does that work? i am supposing white areas mean glossy and black areas clear reflections or  white areas will have pointy/tighter highlights while grey or darker areas will have broader highlights? I am thinking the latter is the more accurate one while u specify in the corona material the glossiness using the parameter between 0-1?

One cannot go without another. Highlights is just reflections of bright light sources. So, tight highlight is glossy reflection of bright light and broad one is blurry reflection.

[melviso]

One cannot go without another. Highlights is just reflections of bright light sources. So, tight highlight is glossy reflection of bright light and broad one is blurry reflection.

So say u have wood that has a glossy surface. For a surface to have blurry reflections it means on a microscopic level its rough. Unlike glass or metals, their surfaces are smooth, sometimes brushed which means their surface are smooth yet brushed causing anisotropic reflection.So how best would one do this in corona for wood for example?
Would using a noise map of dark grey be sufficient or it would be more towards white for the glossiness map? I am a bit confused what values of grey are appropriate to use.
Reflection maps  are quite clear enough as they specify the color and intensity of a surface's reflection.I am guessing glossiness is even more important than reflection maps?To get a surface roughness down the way it is in the real world,would it be best using a reflection map as well. Which one takes more priority than the other?

[Juraj]

Glossiness map. In pure PBR approach, specular map would be unecessary outside of mask for lerping or metals, but in Corona and similar renderer you ought to use both for best results. Still, it's glossy that takes priority for variation.

In glossy workflow 1=RGB255, so white parts of texture will be "glossy" (super stupid and innaccurate name...), sharp highlights with clearly readable reflection and black will make the surface appear rough/matte, with wider, weaker highlights and unreadable reflection.

Regarding wood, wood does actually often have anisotrophy, dictated by grain but in most render engines you set this with anisotrophy paramater, bump/glossy map alone would not create the effect sufficiently. It's rather subtle often, better not overdo unless you have clear reference that you follow.

[melviso]

Okay.That explained it better. Thanks Juraj.
 I am hoping somebody makes a corona shader that's more physical based with only diffuse,roughness,bump,displacement and self illumination. There shouldn't be need for glosiness and reflection slots. Even more physical based would be just diffuse,bump,displacement and self illumination.Roughness should be determined by bump and displacement of ur materials. I am guessing that has not been achieved yet.
I do have a lot of respect for software designers. What they do isn't easy.We will all have to manage what we have for now.

[Juraj]

The PBR (Disney based with metalness attribute) shader sorts of does the second thing in games interpretation (like UE4) though. 'Roughness' is really meant only for micro surface variance, something that could really be lots of high-frequency detail, while bump slot (in game engines often left purely just for Normal map) is meant for the low-frequency slightly different detail (very low relief, or bigger scratches, dents,etc, details that don't necessarily change the microscopic structure of material but are nonetheless very visible by our eyes). I too find it very handy.

But it's fine to achieve the same but it's more eye-balling and more tweaking with Corona. It's just important to not overdo things (like super strong bump map containing every detail). Always think of where the details should go (Darker diffuse appear more reflective, so use that not only pure reflectance channel, Reflectance channel can be used as mask for non-reflective parts (like where dirt/grit resides), Glossy should contain the variance between matt and specular parts, Bump should have detail noticeable by eyes, like big scratches or fabric structure,etc..).

When I do materials I always think of 'Bertrand's rule' : "Once I come with something I like, I tone it down". (not that I am sucesful doing it :- D but I try to keep it in mind)