Need some help with roughness maps
Hi!
I am trying, but can't find a good answer online so I ask you.
As I understand PBR not metallic workflow. Linear is in 0 - 1 value space and Srgb is in 0 - 255 and that should be used for some orientation when texturing in Ps or similar software.
Albedo should be in 50 - 240 Srgb range, good.
What about roughness maps? That that applies for them as well or not?
Can someone tell me what values should be for base orientation in 0 - 255 space for roughness maps. Matte, rough materials have bright roughness maps, but what about values?
Currently I am doing some landscapes and I use roughness map values in 150 - 220 Srgb range. That is for rough materials like stone, rock, foliage, grass, soil.
I don't know is there a site with base values for roughness maps for orientation?
Rocks:
Stone:
Soil:
Gravel:
Ice:
Water:
Snow:
Grass:
Foliage:
I am confused by 3ds max vray reflectivity slot. They say that reflectivity map for materials like rock should be 0.04 linear, what is very dark but in online tutorials I see reflectivity slot as completely white.
Please correct me if I am wrong and add some details. I want to understand that.
Thank you, guys!
Replies
Roughness values should always be in linear space - you will get inconsistent results with sRGB.
In terms of reference, have a look at this: https://seblagarde.wordpress.com/2014/04/14/dontnod-physically-based-rendering-chart-for-unreal-engine-4/
roughness represents microsurface detail that cannot be represented by a pixel, it is an average over an area.
There is no correct roughness value for a surface - any charts or reference that you see must be taken with a pinch of salt.
in practice you need to eyeball it under the lighting conditions you'll be working with
the reflectivity slot in your vray thingy is the same as the specular map in the spec/gloss pbr workflow
The difference is that values in the specular map are normalised - white(255,255,255) is 0.08 and black(0,0,0) is 0.0
for a non metal you will usually use a mid grey ((127,127,127) which comes out as 0.04
for a metal you'll use a value closer to white - these are the values you'll find on the various pbr color charts. They are never quite grey
Thank you Benjammin!
The problem is Photoshop color picker is in srgb and there is no linear option, same in 3ds max if I am not mistaken.
I tried to calculate values by using that as a reference:
https://marmoset.co/wp-content/uploads/2014/01/materialref03.png
Roughness:
Material Linear Srgb 0-1) Srgb(0-1) Srgb(0-255)
Canvas 0.53 0.76 194
Rubber 0.59 0.79 202
Plaster 0.70 0.86 219
Brick 0.57 0.78 200
Rock 0.61 0.81 206
Dirt 0.57 0.78 199
Coal 0.39 0.66 168
Leaves 0.41 0.67 172
Wood 0.42 0.67 173
Concrete 0.50 0.74 188
Mud 0.34 0.62 157
For reflectance:
General 0.04 0.22 57
Some materials can have a little more, it depends,...
Hope I calculated them right.
Never felt a necessity to measure roughness to get realistic material. Usually it's so obvious visually. Besides same kind of material could always have some variation in roughness and still look perfectly real mostly.
Also based on my gamedev experience it's pretty much dependent on a game implementation and while called PBR is never perfectly realistic for every angle of light. It may give perfect highlight spot at higher sun angle and too much at lower angle because the shader ignores all those micro shadows those micro , less than pixel bumps start to cast probably. Also contrast roughness pixels make subtle halos usually ( not only metallic ones while much less visible although) . So anyway you have to make trade offs all the time and see how it works together with a normal map.
Also some materials, like asphalt for example , a porous something with a mix of very shiny and not so much grains with sharp edges are never looking perfectly ok in a typical games styled PBR. Ok at midday and not so much at sunset and vice versa .
Generally, I like to match the roughness with a constant value to photo/video reference, and then figure out a minimum and maximum roughness and how much contrast it has in the roughness. Obviously dirtier or more varied surfaces have more contrast and variation in the roughness. Places where people might touch the surface or walk on the surface are going to either increase or decrease the roughness. Often how the surface is finished has more to do with the roughness than the material itself, concrete can be polished to a mirror finish or raw and dusty, almost completely rough.