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GI Light Transfer Study

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  • GI Light Transfer Study

    This is a simple yet interesting experiment I recently produced:

    Global Illumination radiance works through the transmission of light bouncing off various objects and taking a predetermined amount of that object's diffuse color with it, in order to combine it with the next object it encounters. By setting a secondary bounce limit, you can increase or decrease rendertimes significantly and control the amount of environmental light distribution throughout your scene.

    This simple experiment was produced in order to test the relationship between light bounces and rendertimes, as well as study the resulting effects of adjusting these variables. In theory, the more secondary bounces you allow the renderer to have, the further the light will transmit throughout your scene, provided that the diffuse colors are bright enough to bounce enough light.

    To test this, an enclosed model was created and a VRay light was placed at one end of the structure. The model provided a complex tunnel for the light to transmit through, with an opening on the opposite end for the light to exit. The walls were colored full RGB white. A series of renders were then produced, each with an increasing number of allowable light bounces. Naturally the rendertimes increased but it is interesting that after reaching a large number of bounces, the rendertimes did not increase as significantly as with lower light bounces.




    And for the coomplete results, go here and click on Images:
    http://www.richardrosenman.com/project/?cid=163

    -Richard
    Last edited by richard_rosenman; 13-05-2008, 10:13 PM.
    Richard Rosenman
    Creative Director
    http://www.hatchstudios.com
    http://www.richardrosenman.com

  • #2
    nice experiment, thanks for sharing.

    I found it interesting:

    that after 10 bounces the light seems to get very grainy. Id be interested to see what can be done to smooth this out?

    After 50 bounces the rendering times didn't seem to increase but between 5- to 10 bounces, the rendering time doubled

    would be cool to see a real world test to compare with. I would expect that the regions illuminated by the higher numbers of bounces would be less grainy and have a nice subtle almost black gradient to them

    Your test illustrates to me that the sweet spot in terms of bounces has to be somewhere around 10. If you want a faster render, drop to 7-8. If you want a good quality render, go over 10 but maybe not more than 20 to avoid the grainy effect

    what happens if you have 1000000 bounces? :P

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    • #3
      I assume the grain is caused because with every bounce of light, a certain amount of rays are bounced back towards the entrance of the tunnel so that after a while increasing the number of bounces doesnt increase the quality of light as there's only a few rays left to bounce around?
      If so, then the number of rays cast by the light needs to be increased. Ofcourse, I'm probably misunderstanding the way vray works completely!
      Many Thanks
      Patrick

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      • #4
        very nice test, definitely something I'm going to try here too
        Schoonheid vertroebeld de geest

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