How incorrect geometry can affect the lighting of a 3d scene

A little introduction
After having written the latest tutorial on linear workflow, I have received an email from Jackie (a frequent reader of this blog), who claimed that he had followed the instructions shown in that tutorial, but still ended up with washed out renderings.
After having seen the rendering that he had attached to that email, I suspected that he had missed one or more steps.
So I asked him to send over the scene, and promised to do a case study which initially I thought it would be something like “be sure not forget to…. when using lwf”.
It turned out I was wrong; Jackie had followed every step of the tutorial, but still ended up with a rendering that was lacking contrast a bit.
What was the problem then?

Take a look at the following 2 renderings: (click to view a higher res version)


Would you believe that those are rendered with the same lighting and rendering settings?
Actually they are. The only thing that is not the same is the geometry.
I realize it may sound strange, but the way you model your scene may have a very big impact on the lighting.
Take a look at the following renderings:

As you can see, the way the geometry is modeled, environment lighting is getting into the scene through all the wrong places. There is no wall behind the camera, the ceiling is only modeled where it is visible in the camera viewport, etc, etc.
Also, because of this, the lighting cast by the “light emitters” bounces out of the scene in an unnatural way, and all this will only result in a rendering that lacks contrast.

Bellow are a few images that illustrate a few changes made to that scene.

As you can see, the walls are modeled even where they are not visible in the view. The only thing that I left out (on purpose) is the area above the staircase (where there is actually a vray light that simulates a diffuse lighting source that is not directly visible)

Although this may not seem like a regular “3d lighting tutorial”, looking at the differences between the 2 scenarios, made me believe that this can be even more valuable than a “step by step approach to interior lighting with vray”.

Most of the times details like this are overlooked in regular tutorials. I am absolutely positive that I wouldn’t have thought to write about something like this if Jackie hadn’t mailed me the scene.

The conclusion that we can all draw from this is that no matter what rendering engine you use, be it Maxwell, vray, brazil, fryrender, mental ray, it can not calculate correctly the lighting of your scene if the geometry is somewhat incomplete or incorrect (doesn’t matter if the rendering engine is physically accurate or if it uses a biased solution).

Note: In order to make this tutorial more clear and simple, I have modified a little the scene that Jackie had initially sent me. His scene was a little bit more complete, but still the effect was visible so I had to make it even more visible, just for the purpose of this tutorial.

9 Comments
  1. jackieteh says:

    Thank you very much for your help and guide on this scene,i learn a lot from you,hoping this tutorial could help others too,my respect to you,Mr Alex.

  2. Thank you for letting me using your scene to make this tutorial.

    And by the way, you don’t need to call me “Mr” :) “Alex” is fine :)

  3. Diana says:

    We enjoy a lot your tutorials alex, thank you. It would be nice to keep on this kind of process: working on users experiences and sharing.

  4. Thanks Diana!
    If a reader approaches me with a problem, and if time permits it, of course, I’m glad to help. If that particular subject is suitable for a post on this blog, it will definitely become one :)

    Thanks again for the feedback, and hope to see you around here more often.

  5. pep says:

    untopical tutorial/teach, so practical.

    thank you very much (again).

    best regards

  6. Marama says:

    Sir thank you for this tutorial. I’m a novice to 3d art and was a little afraid that the tutorial would fly over my head (It would be 3d tech speak) Thank you for presenting it in easy-to-understand terms for us novices. The render images helped too.
    regards

  7. oluchi says:

    Hi, this is very insightful….However could you show a tutorial on how to actually model this scene. I am having trouble placing my cameras and modelling an interior scene. Thanks a lot.

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