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Resolved Weird underglow with physically based sky - finally found the issue

Discussion in 'High Definition Render Pipeline' started by akent99, Sep 19, 2022.

  1. akent99


    Jan 14, 2018
    Hi, I asked once before (sorry cannot find that thread again!), but I think I worked out where the weird bottom up light is coming from. For example,


    There is no light from below, only a directional light above pointing downloads. Where is the bounce light coming from?

    I started a new "HDRP 'outdoor' scene" and put a sphere in it. The bottom looks lighter.


    I put a big cube above it (so the sphere is in the shadow). The bottom still looks lighter.


    I tried an eye dropper to sample the color in case an optical illusion. At the bottom its #36302E. At the top its #19243E - overall, it is darker (but more blue). The cube and sphere are both using the default HD material.

    If I turn off the cube and Sky and Fog Volume created in such scenes, its even more pronounced.

    Turns out with in Visual Environment, with Sky Type = Physically Based Sky and Ambient Mode = Dynamic you get the glow from underneath. Change it to "static" and it goes away! Static however is documented to use baked lighting for the sky and I am using 100% real time lighting. So I put it back to Dynamic.

    Then I finally found "Ground Tint" under "Physically Based Sky". I set that to black (it was brown), and the weird underglow goes away! So finally solved the problem.

    Attached Files:

    Win3xploder likes this.
  2. HIBIKI_entertainment


    Dec 4, 2018
    To note, when you use Static with PBS you can essentially decouple the visual environment from the lighting environment.

    When you do this the static environment can then be chosen from the lighting panel windows > reading > lighting > environment

    by default, if you only have PBS in your volume in use then it'll just use PBS as is, and PBS changes in the volume would look the same, as both your visual and lighting environments are the same

    Then ambient probe remains regardless of your static environment probe until you start considering probe overrides of the scene.

    If you decouple and switch to an HDRI for example, then you can see the visual environment is still PBS but the lighting environment is the HDRI, and in the video example, this scene has essentially nothing in it. the ambient probe rim light is still the PBS and is red.

    If you were to have a decoupled environment, you can see what happens when you intro due a reflection probe to the scene.

    similarly, if you're using PBS as a static or real-time reference, you can use an HDRI in the Ground Colour Texture slot or change the tinting like I had been doing in the videos.

    Last edited: Sep 21, 2022
  3. Remy_Unity


    Unity Technologies

    Oct 3, 2017
    The ground tint in the BPS sky is here to mimic the ground indirect diffuse reflection, and should be set to match the ground in you scene.
    In the first screenshot you've posted, I see you are in an interior setup, so maybe you don't need the PBS sky in that case.
    Also, for this type of cases, it's always good to bake lightprobes, that will contain the indirection lighting with the consideration of the environment.
    HIBIKI_entertainment likes this.
  4. akent99


    Jan 14, 2018
    Thanks for the replies. The first one I am going to have to read a few more times to understand it I think :).

    Regarding internal vs external scene - this scene is both. It is a school building on school grounds. I think the way I would address that is separate scenes for shots that are inside the building vs outside the building. I am doing that already for day vs night now related to indoor and outdoor lights being on and off.

    I was trying to minimize complexity (number of things to learn) so was using realtime lighting for everything. I rearrange rooms, animate furniture positions, turn lights on and off (although I am trying to reduce this now) etc. Not having very deep knowledge of baked lighting, I did not know how how to control what is baked vs not baked and get it looking "right" for all cases. I started with a scene file with say 50 camera shots - but it is looking like I need to consider creating new scenes more often so I can change scene level settings for different shots more frequently (day vs night, indoors vs outdoors, possibly even different rooms in the same building).