1. Join Date
    Jul 2007
    Posts
    532
    #1

    New feature: SSS

    Introducing SSS in NOX.

    SSS is based on reflections with imaginary particles inside object. What I mean actually there are no particles. It is only a probability that there would be a particle. Light goes through geometry with diffuse transmission and collide with particles until it finds geometry. Then transmits outside with diffuse again.
    Limitation here is that geometry for going in and out should have same material, otherwise ray will vanish. So careful usage is recommended, especially with open/close objects and other objects inclusion and intersection.

    Density tells how much minimum particles ray finds on 1 meter distance. Maximum is 10 times higher. So this value is scale-sensitive.

    Direction allows to control reflection direction during particle collision. Positive value will random directions more like direction before collision, negative value will give more oposite directions. For 0 value all directions have same probability.

    One thing has to be told. Setting SSS enabled is not only requirement to turn it on. Rough has to be set to 100 and transmission turned off for SSS layer. For glossy etc. reflections simply create another layer without SSS.

    Color for reflection 0 and 90 are ignored in SSS layer. Transmission color (despite transm. turned off) is used for SSS (not distance dependent). Also absorption color can be used (distance dependent).
  2. Join Date
    Jul 2007
    Posts
    532
    #2

    Here is a bit of explanation of SSS dir (collision direction). As said before ray that goes through sss object can collide with imaginary particles. Direction setting tells what directions should ray likely take when that happens. Positive values for same as before and negative for opposite. This is shown on attached image. Also sample comparison renders - here density is set with value so there should be at least one collision.
  3. Join Date
    Jul 2007
    Posts
    532
    #3

    A few words about SSS density. It tells about imaginary particles density in object. More precisely how much particles there would be on 1 meter long ray... for example for density=5 ray would collide with 5 to 50 particles... so minimum distance between particles would be 2cm and maximum 20cm.
    That is why object scale counts when it comes to sss.

    Here are some comparisons of different densities.

    Monkey head was bounded by box 3.1 x 2.8 x 2.3 - so quite big geometry.
    Also this is example for problematic geometry - eyes and head are not connected, so there is a hole in geometry. Also part of eyes geometry is expanded under face geometry and sss rays stop there. It is visible as darker areas around eyes.

    Candle had also a bit wrong scale. It's height (not counting flame) was about 23cm - quite big. So sss densities here had to be decreased.
  4. Join Date
    Jul 2007
    Posts
    532
    #4

    A few more samples from my tests...
  5. Join Date
    Apr 2012
    Posts
    3
    #5

    -

    will you add some of these new feature info in user's manual? it will be good be quite convenient

    great stuff, really getting better and better. sss is simple and effective. i have also tested bump mapping quickly and i must admit it works great, especially the wonderful interface which shows the future bump effect better then mental ray one.

    also- is it only my imagination or is the new nox version working faster?
  6. Join Date
    Jul 2007
    Posts
    532
    #6

    Thanks for appreciation.
    I don't think it is faster, at least don't remember doing any tweaks nor optimisations for a few updates.
    Guide will probably be updated once I find time to do it.
  7. Join Date
    Jul 2007
    Posts
    532
    #7

    Some SSS code was updated on path tracing before connecting it to bidirectional path tracing. Just simple tests on different settings. Except for last render all have 90 (weight) SSS layer and 30 (weight) diffuse layer. Figure is about half meter tall. Same color was set on reflection 0 color in diffuse layer and in transmission color in sss layer. Absorption color was dark gray.


    dens - sss density
    dir - sss direction
    abs - absorption depth (or not used)
  8. Join Date
    Jul 2007
    Posts
    532
    #8

    It turned out even on path tracing SSS was bugged. It was working almost correct for direct lighting, but was not cutting out energy for gi, so final color was quite washed out. Here are results after fixes...
    Last edited by marchewa; 2013-01-28 at 12:18 PM. Reason: forum compressed jpeg too much
You need to be logged in to leave a comment. You don't have account? Register now.
Best of Evermotion
The best works from the Forum Gallery picked by Evermotion staff