Question about PBR
polycounter lvl 4
Hi
Im trying to wrap my head around PBR without luck. My biggest problem is visiulizing it. Could anyone post a set of textures that are PBR ready so that i can see more or less how it looks?
Any help would be appriciated !!
Im trying to wrap my head around PBR without luck. My biggest problem is visiulizing it. Could anyone post a set of textures that are PBR ready so that i can see more or less how it looks?
Any help would be appriciated !!
Replies
Your final material will interact with it's final environment (reflections are the greatest exemple in my opinion). That's the main difference.
For example, in Unreal Engine 4, you have to forget Specular Maps. You now use the Metallic parameter and the Roughness parameter. These parameters allows artists to increase the visual quality and credibility of the render.
If you don't understand, maybe someone will be able to explain better ^^
Samuel.
Note : Watch this. http://www.polycount.com/2014/05/30/pbr-comes-to-gametextures-com/#more-14506
To answer your question, AO stays a separate map. Albedo generally does not have AO maps baked into it like with diffuse maps.
So, to sum it up.
Diffuse -> Albedo
Specular -> Metalness
Gloss -> Roughness
Is that kinda sorta it ?
But then how do you get something like leather jacket coated to appear shiny ? It would reflect light, but it's not metal. Would I give it some metalness and some roughness both ?
Albedo is colour with no shading at all.
Roughness is how rough the surface is, low values mean a mirror like surface, high values mean a more diffuse reflection and surface.
Metallic jusut defines if it is metal or not.
It is needed since when something is metal, it will use the albedo input as the reflectance map, since all metals have a near black albedo.
I'm the case of non metals, the albedo is just used for colour, since all non mentals have a very similar reflectance non mentals use a hard coded reflectance value.
Some background first. The metalness map was made to save the use of another full color map for specular/ reflectance. Metal has no diffuse so for the most part when texturing metal you can put black in the diffuse. Also most every other material except metal falls with in the same specular intensity. So the made they metalness map.
First what it does is it take the metal area ( white in the metalness maps) and it makes the diffuse black. Then it takes what you paint in the diffuse in the metalness areas as the specular power/color control. Everything that is not a metal gets a standard specular power and no color.
To make maps using this you simply use the metalness map to separate out what you want to be a metal. Then in the diffuse instead of painting diffuse for the metal you paint what you want for the specular power/ color. The mask should pretty much black and white. If you have gray values you will get some weirdness.
Anyway, Metalness, as far as I know, is unique to Unreal's solution. They lock the SBR to that of plastic except in the case of metals, the values of which are defined in the Diffuse Albedo map (since metal is black it would otherwise just be a bleck hole in the texture), with another map to mark where things should be treated as metals or not (this is my understanding at least, and seems right based on what stevston89 said above).
For other engines it varies wildly, but you generally have two or three reflectance 'masks'. One defines the Specular Base Reflectivity value, one the roughness, and in some cases a third is occlusion.
The value of the Specular Base Reflectivity is usually very low (there are some lookup tables online), except in the case of metals, where it can be extremely high. Since it's so low an SRB map for a non-conduction material is very dark, often looking basically black unless it's seen on a black field. If the value isn't known you can just set it to a plastic value, which Unreal chose to lock to since the range is so small (though it can make a surprising amount of difference).
How Roughness looks depends on whether the engine has white as high or low. Your roughness for a given material will usually also be in a narrow range though. So, unless there are multiple types of material on the same map, a roughness map is going to have very little contrast to it (though a single material might have more contrast for stylistic reasons), again this makes the map fairly hard to read without increasing contrast.
Finally the Occlusion Map masks out where reflections can be. This is different to a specular base reflectivity map because an SBR of 0 (which is an impossible value BTW) will still result in a reflective material, because everything is reflective. Sometimes, even though everything is reflective, what it's really reflecting is another surface thats in shadow, resulting in a much reduced visual brightness. Other places you might not want a reflective surface are holes where you don't see what's beyond them. Examples of that would be the gaps in a vent for example, or a thin seam between two metal plates. Occlusion works on basically the same principals as Ambient occlusion, and looks a lot like an AO map - generally I just throw a baked AO in there and it works just fine, though sometimes the contrast needs some adjustment.
Despite the preference being to call it an Albedo map now, a diffuse map does pretty much what it always has done, but it now carries less information since more is handled under Specular (Reflectance). You don't need baked AO on it (or at least you need a lot less), and as mentioned Metals are painted as either Black (SBR) or the color of the metal (Metalness). This leaves Albedo maps looking a lot flatter, and generally just carrying colour information rather than brightness. Normal maps are also handled the same way as they were before.
For a rough idea of how all this works, treat your roughness like your old specular map, and your occlusion like your old AO bake and you'll quickly get a handle on the SBR or Metalness aspects because you're only worrying about really learning one thing. Once that's down experimenting with the other two becomes easier.
Great post, just a few things here that I think are important to clarify:
Generally, what you're referring to is called a reflection occlusion mask, and whether you need one of these varies heavily on the engine (as you pointed out above), I think referring to it simply as occlusion is little confusing. Reflection occlusion isn't really the same thing as AO, and you generally shouldn't throw an AO map in a reflection occlusion slot (though it can make sense to make a refl occ map from an AO base), unfortunately there really isn't any standard way of generating reflection occlusion. Reflection occlusion should block specular reflection from ambient image based lighting (IBL cubemaps) but not direct (dynamic) lights. If your engine has real time (screen space or otherwise) reflections, generally there is no need for a reflection occlusion map.
Here's a variety of types of occlusion from Modo's help docs: http://docs.luxology.com/modo/501/help/pages/shaderendering/ShaderItems/Occlusion.html
Ambient occlusion on the other hand, with modern shaders, should only be applied to the ambient diffuse lighting (diffuse IBL) component of the shader, which is why its important not to bake AO into your diffuse/albedo with PBR shaders. When an AO map is used to mask direct diffuse lighting or specular lighting it tends to look wrong/dirty.
A cavity map is also common, and generally will be applied to both the diffuse and specular components for ambient and direct light. The basic theory here is that micro occlusion from small divits, cracks, etc is difficult to represent accurately without more sophisticated rendering techniques, so its okay to mask specularity in this case, even from direct light sources.
Well, Y'see? This is what I'm talking about - there are no real standards as yet, and might never be, including (in some cases), what to call things. You're right that I should have called it a Reflection Occlusion, except in-house we refer to it as a Specular Occlusion, and it does in fact act as a cavity map (if you want the cavity map to effect both the spec/reflection and the diffuse you can do that).
In many cases you can totally get away with using an AO map for it, though it generally needs the contrast and gamma to be adjusted to avoid it removing the reflection from the big areas (which you might want to reduce a little, but in many cases you'll want to leave alone; especially with SSR as you also noted). If there is no SSR (or raytracing or whatever) then you might want to reduce the reflectivity even in the large areas of occlusion so that the big white wall the cubemap is picking up on isn't hugely reflected right through the black painted bump out you have intersecting. It's not perfect, but it's something.
All that said though, you would probably approach it differently in different engines as you observed. And true, an AO isn't always going to be a good base for such things, but it's easy to create one and see. If it works with some fiddling you've saved yourself some time (and hooray for that). I've not had the chance to poke at Modo, but if it results in a dirty look there then I guess it's best avoided in at least that case, and other renderer's with a similar option set.
What any of these occlusion style maps should not be used for is generally reducing the overall reflectivity of a surface, such as where grime has gathered. I've seen that done a few times, but that's what the Roughness and SBR values are for. In general anyway - you could, under certain stylistic circumstances, but not if you're going for believable surfaces.
Hey dude, yeah, there is of course variance in implementation. My post above was as general as I could make it though, and talks more about ideals than any specific engine. Specular vs reflection occlusion, that's just a difference in terms, those are basically synonyms, specular reflection being the full term.
Ok, now this confuses me. Is it a spec/refl occlusion map or is it a cavity/micro occlusion map? These really aren't the same thing (and again, I'm not talking any specific implementation, these are pretty well defined terms in rendering/games industry). Again for a spec/refl occlusion map, you do not want that to multiply on your diffuse contribution, or onto your direct lighting (diffuse or spec), because it doesn't make sense physically.
So, I would be curious to learn exactly how you're applying this map in your shader (eg, what does it effect? ambient reflection only? ambient and direct reflection? something else?).
So the important thing here is exactly what your content looks like, or what your bakes specifically look like, if you have small scale AO, its easy enough to do some levels/curves on that and pull out a cavity map. If you have large scale ao, you can do some adjustments to get a pretty good reflection occlusion map, but it would be a poor source of content for a cavity map (cavity/micro occlusion maps should not have large scale AO detail).
So here is a practical example. Lets say you have a helmet, when you bake your AO map, the inside of the helmet gets really dark. This can be thrown on the diffuse pass as is, but only on the ambient diffuse pass. If you throw it on the direct light pass, what that means is that if you shine a dynamic light into the inside of the helmet, it won't light up. This doesn't make physical sense, and is why the AO map should be applied as a separate pass, only on the ambient diffuse. Even here, depending on how sophisticated your renderer is (realtime ao/ssdo?) you may want to avoid large scale AO in the ambient occlusion map as well.
Similarly, if you throw that same AO map with large scale detail onto your reflectivity pass (both ambient and direct) what you're really doing is tagging that inside area as less reflective (the material type hasn't change at all so this doesn't make any sense). If we throw a direct light on that area again, it will not reflect at the appropriate brightness if your reflection occlusion is masking direct specular lighting.
So yeah, its heavily dependent on exactly what your AO content looks like, which varies by any number of factors including how and where you bake it. I wouldn't recommend throwing baked AO into reflection occlusion or cavity slots unless you really know what you're doing (I'm not saying you don't, I'm saying this could be confusing to less experienced artists who may not understand the finer points). In general I don't think artists should do this on a per-asset basis either, in an ideal case your TD/tech artist will come up with a reliable workflow here than you can apply on a wide scale. At the very least you should have some sort of refernce art for what sort of content these maps should contain so artists have a target to shoot for instead of eyeballing it per assets. A big part of PBR workflows is consistency, so if artists throw AO maps into reflocc/cavity slots without really knowing what those slots do, it throws a wrench into the system.
So generally an AO map looks something like:
While a cavity/micro occlusion map looks something like:
Not that your content HAS to look like this or anything, just as an example of how content may differ for various input types.
Yeah, if we're talking micro occlusion here, seam lines, cracks, etc, I totally agree.
The Modo link is just one of the better visual examples I've seen of the various content sets, I don't actually do my bakes in Modo.
The comment about dirtiness isn't specific to Modo either, and it isn't really a new idea. The basic concept is that if you multiply AO on everything, it looks bad, and isn't physically accurate for various reasons outlined above. Again, I'm not talking about any specific implementation here, more as a general concept.
Yes, I think we agree here, and much of what I've wrote above basically expands on this idea. I've seen in a lot of previous gen workflows (and did it myself as well) where AO was used basically on everything without regard to where it makes sense to use, which results in surfaces becoming less reflective where the AO is stronger, which doesn't make physical sense again, the material hasn't changed. Roughness is generally the area you would represent gunk and grime built up in cavities, and often times you can use an AO map as the basis for masks for certain effects, but not generally as a direct multiply, for instance, if its grease built up in the crevices, you might want that area to be glossier rather than duller.
I think what you're describing in that last quote is really just a cavity map from my understanding of the word (and most PBR implementations I've researched). So we're back to implementation specific terms, hehe.
Anyway, for obvious reasons I can't say too much about propitiatory tech, so I won't go into details there. In general though, yes, I've been talking about cavity maps; although a cavity map is just a high frequency occlusion map, there is a difference in the overall result (you can create a quick n' dirty cavity by running high pass on an Occlusion map and then adjusting the contrast - though the results are nowhere near as accurate as a true cavity pass because the AO isn't accurate enough). I tend to have a lot of success with a cavity map merged with a low contrast Occlusion, although, as you say, too much and it makes things look dirty - and you wouldn't need to do this if you have a pixel accurate reflection anyway as the reflection will do the job for you (You'd still likely want a cavity map in this case).
I really need to make a note to come visit at least once a week. Life, as the commercial says, comes at you fast
Metalness: it controls how much something reflects. So the difference between a chrome ball and a rubber ball. Obviously a chrome ball is very mirror like, right?
Roughness: It controls the amount of shine. It dictates how much fall off there is on the object.
You need to find a balance between these two.
albedo: where the color information is stored. This is very important, learn the actual materials color without any lighting or reflectivity. So where copper might be naturally black, but it gives off a copper shine, you'll add the color of the shine in later.
Microsurface: The roughness, so if your item is a dirty metal, a dark splotch on the metal won't cast reflectivity / catch light.
Reflectivity: What color the shine / reflection of the material will be. You can kind of see in the example how it will work.
Normal maps stay the same, for the most part.
Now the other way I've seen is this way:
http://artisaverb.info/Cerberus.html
This way involves the same maps but put to use in a different manner:
Albedo: Same thing. Pure color map without shadows.
Metalness: Most of this is going to be pure white or pure black. A pure white means it is a metal and will catch a reflection, a pure black means it's something like rubber or wood. You can vary with greys or not, but the majority of it is going to be black or white.
Specular: Where you dictate how much the metalness is going to reflect. So for example, if you had a chrome ball, your metalness would be 100% white, but if you wanted to dirty it up and not make it reflective, this is where you would begin to edit it.
Normal map: same as always.
That's how I've understood it so far, and as an example here's a crowbar I've made. It may not be the best but it may serve the purpose:
What I've done here is created the basic albedo map, if you notice. Then since everything is metal, I made it mostly white, but I didn't want the crowbar to be a mirror. So I very, VERY lightly made it less than white.
Then came the roughness. The metal part, I wanted to catch a lot more light, so I kept it a fairly bright color, but when it came to the painted part, I made it a lot darker and red, so it'll catch a red specular and not be almost mirror like. You can see the crowbar in more lighting examples here:
http://imgur.com/a/rAgsX
It really just takes some amount of tinkering. Just create a sphere, and play with different values to create different types of materials, like a rubber and a chrome ball. And experiment! Make something with 100% white metalness, and give it no specular at all, and vice versa. Hopefully this may help you wrap your head around it, I'm still new to PBR but this is to my understanding how I've started creating objects.
In unreal the amount of reflection vs the albedo is affected by the metalness. But that's not what the metalness is doing. A material with a low roughness value is very shiny no matter what metalness setting you use.
Metalness is not the same as specular intensity. Roughness controls specular intensity. If you want to make a rubber ball make something with a high roughness.
metalness is a switch between coloured reflections and reflections that are unchanged. A metal object can have a coloured reflection - like gold - a non metal object will always reflect whatever colour is in the environment.
Just to add to this for people that use other engines besides unreal, what the metalness map is doing, is for areas defined as metal, so white in this map, it is sampling the reflectance(colour for the reflections) from the same area of the albedo map, than just giving those areas a almost black hardcoded albedo.
In the case of things marked as non mental in this map, it is using a hardcoded reflectance value, and is sampling all the albedo from the albedo map.
That is how unreal deals with it.
In the case of some other engines you just got a separate reflectance/specular map, where you can define the reflection colour for any pixel.
This is the case in marmoset, where for most matierals in the specular slot, your just going to have a grey with no much detail. But with metals you will want to do too things, add colour and up the values in your specular, and also darken the albedo to almost black.
ahendowski
you will want to take all colour out of your roughness map, all roughness does is define if the surface is smooth(low roughness) or rough. Than in you metallness map you will want to contrast it to have absolute values. Make hte paint black and the iron of the crowbar white.
I think some of your confusion is between how unreal and marmoset take different kinds of maps, but are both pbr.
Just think of metalness as a per pixel Boolean value, "Is This pixel metal?"
The best thing to do is as slosh suggested and get down and dirty with it in a PBR renderer like TB2 or UE4 or something.
Hey, some notes on this:
The Cerberus example is not the most correct one out there. Don't take it as gospel.
Your maps are not exactly correct:
- You're marking paint as being more metal than the actual bare metal. Metallic = bare exposed (untreated) metal.
- Your roughness contains color information, this is not used in any way whatsoever. I have no idea why it's like that on the Cerberus example; one reason it's not a good example to base yourself on.
- All that noise and variation in your albedo should probably be in your roughness (too).
Asa final note: you should really consider using something like a 256x1024 for an elongated object like this, 1x1k is a bit silly if you're going to have all those seams.Some weird info in the last few posts (with the exception of Laurens'), I won't go into great detail explaining the map inputs, because I've already done that here. We did a podcast on this as well last weekend.
But here is a quick summary of the map types again.
albedo = diffuse/color map, but generally without any lighting information baked in (does more with metalness workflow tho).
reflectivity = how much or little light reflects off of a surface, this is a concept not a specific map type, examples of maps to set reflectivity are specular and metalness, neither are more or less physically accurate.
specular = same as old gen specular, sets specular reflection intensity and color explicitly, uses more memory than metalness but gives greater control.
metalness, TB2 supports both btw.
metalness = is a rayscale input that flags whether a material is made of metal or not (painted metal is not metal, its paint, this is used to define the top layer). For metallic surfaces, the specular intensity/reflectivity is pulled from the albedo map, while the diffuse is set to zero (as raw metals diffuse or scatter very little light due to how dense they are and instead reflect most of it). For non metallics, the reflectivity value is set to a fixed 0.04, as most non-metals reflect in a narrow range. Usually you use 0 or 1 for metalness, but you may need grey values for transitions or gradual effects like oxidization.
microsurface is again a concept and not a specific input, to set the microsurface of a material, or how rough/smooth it is, you will use a gloss map, or a roughness map.
Gloss/roughness map, these are exactly the same thing, and serve the same function that a gloss map did in older workflows. Roughness map use an inverted scale (where 0 = most shiny and 1 = least shiny) but not always (depends on engine). Gloss/roughness maps DO NOT CONTROL SPECULAR INTENSITY/REFLECTIVITY. The control how rough the surface is. Due to energy conservation, the rougher the material is, the more the light scatters and the wider an dimmer the specular highlight is, but it the total amount of light remains the same, reflectivity is not controlled by gloss/roughness.
AO/Cavity, explained above what these do.
You will always have:
Albedo
Reflectivity, so metalness or specular, but usually not both, if you have metalness, a specular input is redundant and likely makes it possible to enter values that are not physically accurate (really, people should ignore the specular input in UE4)
Microsurface, so gloss or rouhness, not both, this doesn't replace or need to be balanced with reflectivity or anything like that
The above three are roughly equivalent in older shaders to:
Difuse
Specular
Gloss
Normal maps work the same as they always have.