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PBR grass vs asphalt albedo/base color value?

gnoop
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gnoop sublime tool
Does anyone know why basically any  base color/albedo  gude  says  asphalts including old/worn ones base color  should be darker than any random grass/ foliage albedo and yet  I see it every day  that a grass is usually  darker  through a day   until late afternoon   at least   toward the sun   only  where we se lots of grass translucency/ SSS  and it may look brighter ?   And no physical property even in offline renders could make it look otherwize?        Thats sRGB 80   in top right corner  . A recommended one for old  dusty asphalt .

Sun is behind in this photo at 48 degree elevation  so it's not  that lots of highlight spot /specular lobe here.

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  • Noren
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    Noren polycounter lvl 20
    I would say just use what works for you. Even with worn asphalt, you'll have a host of options (how old, what kind of gravel/aggregate, what kind of bitumen, what kind of dust, not to mention the kind and state of grass or foliage). I can see the appeal of PBR being the be all and end all of material definition (looking at your other recent thread about the topic) but I'd trust my own eyes first (with some caveats--see below--and with testing in different lighting conditions where necessary, which you seem to have done).

    Now let's assume for the sake of argument that really worn asphalt is not just an omission and speculate a bit: With the sun in the back like in the picture, the rougher the material, the more "direct" sunlight will be reflected back to you. The (I assume) less rough grass/foliage will reflect more sunlight back to you when at the right angle, but most bits will be oriented differently and there are lots of holes in the coverage and shadows. The same goes for the bigger light of the sky, just less easy to visualize.

    If we look at the flowers in the foreground, the brightest bits seem also the most saturated, and saturation can play tricks on us regarding how bright we perceive something to be, but I'd say there are both more bright and more dark spots in there than on the asphalt. With the brightness of the albedos given in the upper right corner being almost the same, that sort of makes sense. As for the grass in the distance, it all smushes together. We can make out some brighter waves that might be flowers or the sun or sky reflecting in more blades of grass, but we probably look at more shadowed areas than we realize in that case, too, even with the sun in our back.
    For a direct comparison, you could pin down a blade of grass to the asphalt and see how it reacts to light.
  • okidoki
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    okidoki greentooth
    Maybe because the reflection "factor" of light on asphalt in in total greater than in some plant "array" because of the darker looking spots inbetween and the bending of every single plant part ?? If the final result does fit the reference then the initial darer color does fit this "experience top" ??

    Ohh.. indeed.. just was (double) checking.. see some technical paper from the American Concrete Pavement Association and also the original term via Wikipedia: Albedo (from Latin albedo 'whiteness') is the fraction of sunlight that is diffusely reflected by a body.
    ..so the albedo-"color" is choosen darker ( if i'm not mistaken )  to match better the final result.
  • ZacD
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    ZacD ngon master
    Just googling old road you can see some are darker than the grass and foliage and some are lighter, just depends on the materials and how it aged. Personally I'd start with the brighter concrete curb, put that at about .4 and try .35 for the road and see if that looks right. Charts are a good place to start, but I'll happily use .2 higher than what's suggested if it looks better for my scene.
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