5 ms·

Normal maps influence diffuse lighting as well. All lighting is just light bouncing off of things, I'm not sure why you're quibbling over this.

Jasper_ 7y ago
They're talking about the incoming irradiance vs. the surface reflectance. Both are related to the surface normal, but the former has to do with surface visibility, rather than reflectance. You'll notice that BDRFs don't include the Lambert cos term, since they only describe how they deal with incoming irradiance. Put simply, a surface can't bounce any light if it doesn't receive any light to begin with. It's a weird, nitpicky statement, but hey, that's what this site is about, right? > All lighting is just light bouncing off of things In real-time graphics, bounce lighting is pretty rare. Typically you cache incoming irradiance into some form offline to emulate bounce lighting. Most of our scenes are lit with analytic lighting. A key directional e.g. sunlight for most light, and then punctual sources like point and spotlights for additional lighting tweaks.
robbrown451 7y ago
I agree that normal maps influence diffuse lighting. Not sure I agree that lighting is always "light bouncing off things", since with a diffuse surface, it scatters it in all directions approximately equally. If you consider that a bounce, ok, but it isn't the same as "mirror type" reflection where the bounce angle works similarly to a ball bouncing off a surface (angle of incidence equals angle of reflection). So, I don't agree that the normal's effect on diffuse lighting is on the way light bounces off things, instead it is the quantity of light that hits the surface. I just think he could change the wording (as I suggested) to make it more accurate, so it betters people's understanding of the more general subject. It would be a simple change that would be easy to make, so it's intended as constructive criticism rather than just quibbling.
- Negitivefrags 7y ago
  If you want to quibble, then in reality, there is only specular light reflection. It’s just that rough surfaces bounce light in many directions because the surface is rough. In theory, if you had a high enough resolution texture and used enough samples you could actually represent all materials with only specular reflection. Diffuse light is simply an approximation we use. We effectively have a value for “roughness” of a surface and assume that some percentage of the lights scatters in all directions using various approximations of how rough surfaces typically reflect light. So yeah, it’s always “light bouncing off things”
  - Jasper_ 7y ago
    > It’s just that rough surfaces bounce light in many directions because the surface is rough. Sort of, but not entirely, or you would get micro-flares on the surface, which we don't observe in reality. The other half of the equation is light that bounces around inside the object, and then comes out effectively in a random location. The majority of diffuse light is light that has been subsurface scattered. A huge simplification we make is assuming that that light can be modelled with a uniform constant factor, e.g. Lambertian diffuse. For surfaces with with microgeometry larger than the scattering distance, you need a more robust diffuse model, like Oren-Nayar.
- teawrecks 7y ago
  I think you might be getting confused in the different lighting models. IRL there is no hard difference between specular and diffuse surfaces, that's a separation we've made in rendering for convenience. A raytraced pbr scene will use the normal and the roughness to determine the grouping of the resulting light bounces. But unless the surface is also emitting light, all lighting in the scene is from bounces, even of everything in the scene is diffuse.
  - robbrown451 7y ago
    Pretty sure I'm not confused about it, although it appears I use the word "bounce" a bit differently than you. Specular reflection and diffuse reflection are very different things, at least on typical reflective objects (including water and glass and black things, which don't have significant amounts of diffuse reflection). Here's one of many things I've written on it (and my experiments related to specularity and such go back to the early 80s) https://www.quora.com/Why-does-snow-appear-white-in-colour-while-water-is-transparent-colourless-1/answer/Rob-Brown-13 https://www.quora.com/Why-does-snow-appear-white-in-colour-w...
    - magicalhippo 7y ago
      If you come from a ray/path tracing background, it's bounces all the way.

Jasper_ 7y ago

They're talking about the incoming irradiance vs. the surface reflectance. Both are related to the surface normal, but the former has to do with surface visibility, rather than reflectance. You'll notice that BDRFs don't include the Lambert cos term, since they only describe how they deal with incoming irradiance. Put simply, a surface can't bounce any light if it doesn't receive any light to begin with. It's a weird, nitpicky statement, but hey, that's what this site is about, right? > All lighting is just light bouncing off of things In real-time graphics, bounce lighting is pretty rare. Typically you cache incoming irradiance into some form offline to emulate bounce lighting. Most of our scenes are lit with analytic lighting. A key directional e.g. sunlight for most light, and then punctual sources like point and spotlights for additional lighting tweaks.

robbrown451 7y ago

I agree that normal maps influence diffuse lighting. Not sure I agree that lighting is always "light bouncing off things", since with a diffuse surface, it scatters it in all directions approximately equally. If you consider that a bounce, ok, but it isn't the same as "mirror type" reflection where the bounce angle works similarly to a ball bouncing off a surface (angle of incidence equals angle of reflection). So, I don't agree that the normal's effect on diffuse lighting is on the way light bounces off things, instead it is the quantity of light that hits the surface. I just think he could change the wording (as I suggested) to make it more accurate, so it betters people's understanding of the more general subject. It would be a simple change that would be easy to make, so it's intended as constructive criticism rather than just quibbling.

Negitivefrags 7y ago
If you want to quibble, then in reality, there is only specular light reflection. It’s just that rough surfaces bounce light in many directions because the surface is rough. In theory, if you had a high enough resolution texture and used enough samples you could actually represent all materials with only specular reflection. Diffuse light is simply an approximation we use. We effectively have a value for “roughness” of a surface and assume that some percentage of the lights scatters in all directions using various approximations of how rough surfaces typically reflect light. So yeah, it’s always “light bouncing off things”
- Jasper_ 7y ago
  > It’s just that rough surfaces bounce light in many directions because the surface is rough. Sort of, but not entirely, or you would get micro-flares on the surface, which we don't observe in reality. The other half of the equation is light that bounces around inside the object, and then comes out effectively in a random location. The majority of diffuse light is light that has been subsurface scattered. A huge simplification we make is assuming that that light can be modelled with a uniform constant factor, e.g. Lambertian diffuse. For surfaces with with microgeometry larger than the scattering distance, you need a more robust diffuse model, like Oren-Nayar.
teawrecks 7y ago
I think you might be getting confused in the different lighting models. IRL there is no hard difference between specular and diffuse surfaces, that's a separation we've made in rendering for convenience. A raytraced pbr scene will use the normal and the roughness to determine the grouping of the resulting light bounces. But unless the surface is also emitting light, all lighting in the scene is from bounces, even of everything in the scene is diffuse.
- robbrown451 7y ago
  Pretty sure I'm not confused about it, although it appears I use the word "bounce" a bit differently than you. Specular reflection and diffuse reflection are very different things, at least on typical reflective objects (including water and glass and black things, which don't have significant amounts of diffuse reflection). Here's one of many things I've written on it (and my experiments related to specularity and such go back to the early 80s) https://www.quora.com/Why-does-snow-appear-white-in-colour-while-water-is-transparent-colourless-1/answer/Rob-Brown-13 https://www.quora.com/Why-does-snow-appear-white-in-colour-w...
  - magicalhippo 7y ago
    If you come from a ray/path tracing background, it's bounces all the way.