Albedo material vaules chart?

melviso

Does anyone know where I can find an accurate detailed complilation of albedo vaules for a lot of materials?
I am currently doing some research on lighting and materials. I have found some charts but was wondering if there is a dedicated site for this in both srgb and linear?
Thanks

Eric Chadwick

I've gathered these. Comb through and share what you find, I'll update the wiki.
http://wiki.polycount.com/wiki/PBR

Eric Chadwick

Btw, albedo values should always be in sRGB (or Gamma, basically same).

melviso

Thanks Eric :- )

melviso

@Eric Chadwick
Found this:
https://www.artstation.com/shinsoj/blog/Q9j6/albedo-chart
The color space conversions formula. I am not sure how they are calculated. I tried converting  linear rgb of 0.27 from the picked color  to srgb and I got around 11.33 for srgb. How do u get the r, g, b for srgb vaules from a Linear rgb?
I understand that albedo vaules for dielectric are a combination of both albedo and specular reflected light. So I presume albedo vaules is sort of a representation of the amount of light these surfaces reflect. Then what about the roughness of the surface? Does this involve the roughness of these surfaces that determine how much of the light is absorbed or reflected or albedo vaules have nothing to do with surface roughness at all?

Obscura

Converting from srgb to linear is done by putting the value on power of 0.4545. 
From linear to srgb is power of 2.2.

To convert from 0-1 range to 0-255 range is by multiplying the value by 256.
From 0-255 to 0-1 range is a division by 256.

If its rgb values instead of a float, you need to apply these math on all 3 components separately.

Eric Chadwick

melviso said:

...
I understand that albedo vaules for dielectric are a combination of both albedo and specular reflected light. So I presume albedo vaules is sort of a representation of the amount of light these surfaces reflect. Then what about the roughness of the surface? Does this involve the roughness of these surfaces that determine how much of the light is absorbed or reflected or albedo vaules have nothing to do with surface roughness at all?

Albedo in the Metalness/Roughness workflow does store both Diffuse color, and Reflection color. But... Metalness is a mask between the two. 

Where Metalness is black, Albedo acts as the dielectric Diffuse color. Where Metalness is white, Albedo acts instead as the metallic Reflection color.

So, it's an optimization to store both Specular reflection and diffuse response, in one color texture. With the Metalness acting as a mask between the two different material types.

Roughness is a separate control entirely. Albedo has nothing to do with Roughness. 

You might see something funky if the BRDF is not great at energy conservation... then full Roughness will decrease the brightness of the total light bounced off the surface, full Roughness making surfaces get darker.

This is physically incorrect though. The surface should be about the same brightness overall, whether it's zero Roughness or full Roughness.

Hope that makes sense. It's a bit weird to wrap my head around, but that's what I understand of the PBR talks and papers.

melviso

Thanks a lot mate, are the equations in that link wrong?
mutiplying 0.27 with 256 gives 69.12 which is close to the brightness vaule of the color picked in artstation post- 67%

why 256? Isn't it supposed to be 255?
How do u use the albedo chart tbh in ue4 or offline renderers?  say Terracotta tile- 0.28. Convert 0.28 to srgb- 71.4, right?
So, that is the brightness vaule for whatever color u are going to use for terracota in srgb?

Eric Chadwick

I think it's supposed to be 255, not 256?

255/255 = 1
etc. 

melviso

@Eric Chadwick  Thanks Eric. I agree. I think I have noticed situations where roughness makes the diffuse look darker when working with offline renderers. I will have to pay more attention to this next time. So how do u use say albedo vaule for example if Conifer Forest - 0.08 for offline renderers? U convert to srgb 0- 255 range? Is it the vaule of brightness for the color in srgb- 0.08 x 255 = 20.4?
@Obscura I am tying to get what u wrote:
From linear to srgb- 0.27^2.2 ?
or 0.27 x 255 to convert to 0- 255 range, so where is power of 2.2 used?
Could u pls look at the equation in the artstation link
https://www.artstation.com/shinsoj/blog/Q9j6/albedo-chart
Is this correct?

Eric Chadwick

We don't use albedo charts here. We're replicating real-world objects from photo reference and scans.

melviso

It's confusing. I have to admit but this will help to ensure u are close to real world materials that work in different lighting conditions. I heavily rely on eyeballing so having a chart helps u start from somewhere.

Obscura

Hi @melviso. I don't have much time at the moment, so can't try the formula from artstation properly, but at first look , they look overly complicated for no reason. There are unnecessary multiplications and divisions, but they also show "power" in them. Maybe those multiplications and divisions are for value range shrinking and extension. You know from school when there is a little number on the top right of the number and it means how much times to multiply a number by itself? Thats power. If you still don't get it, I can write more details later when I get home. Let me know.

Obscura

Also, I think you are overthinking this topic a little bit, because all material editors allows you to quickly apply correction and to convert from srgb to linear and vice versa. For example in Unreal, you can simply tick a checkbox. Or put power node in the material and input that 0.4545 if you want to convert from srgb to linear, or 2.2 if you want if you want to convert linear to srgb.

melviso

@Obscura Ok.  Thanks.