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  • Saturn Rings – backlit? light scattering? light transmission?

  • Corrado Carlevaro

    November 3, 2010 at 4:35 pm

    Hi,
    I want to create, say, Saturn and its rings. The rings are just a bidimensional disc, I’ve got Color Map, Alpha Map (plus black and white maps found in Bjorn Jonsson site https://www.mmedia.is/~bjj/data/s_rings/index.html representing the scattering of the light from different angles).

    Problem is that the rings of Saturn are lit also in the face opposite to the sun. How would I do that? Of course I can’t use the luminance channel because the rings are lit in both faces but shadowed by the planet itself. How should I use those maps, at least the “Unlit side” map?

    Thanks in advance

    Corrado Carlevaro

  • Alan Flood

    November 3, 2010 at 11:07 pm

    Hi Corrado.

    The simplest way to do this would be to render two passes and then composite them together in post to get the desired effect. Render one pass with normal lighting to capture the sunlit side of the rings then render another with different lighting setup – set it up so that the rings look the way you think they ought to in shadow of the planet. Then it’s just a simple matter of layering the dark pass over the bright pass in something like photoshop or GIMP and masking out all those areas that lie outside the shadow area.

    I hope that helps 🙂

    Alan

  • Adam Trachtenberg

    November 4, 2010 at 2:44 am

    Use the Effects>Backlight shader in the luminance channel.

  • Corrado Carlevaro

    November 5, 2010 at 12:49 pm

    Thank you very much.
    One more question about Backlight shader, if possible. How would you use texture maps (Bjorn Jonnson’s site B&W maps representing material density and light scattering) there, since it’s not possible to load textures in Backlight? Maybe with Layer shader and some kind of blending mode (Multiply)? Where can I find some explanation about Fusion shader?

    Thanks

    Corrado

  • Adam Trachtenberg

    November 5, 2010 at 3:17 pm

    You can use texture maps with backlight with the fusion or layer shader. Fusion is basically an earlier version of the layer shader which has been retain mostly for backward compatibility. I’d recommend that you get in the habit of using the layer shader instead of fusion because it’s more powerful, although the fusion shader can be easier to use if you’re only combining two layers.

    You can think of them both like Photoshop or AE layers. Fusion allows two layers and one alpha in between, and you set the mix mode just as you would in PS or AE. The layer shader works along the same lines except it allows you to combine as many layers as you want.

    In this case you would probably want to multiply your bitmap over the backlight shader.

  • Corrado Carlevaro

    November 6, 2010 at 3:01 pm

    yes, this is what I’ve read in the meanwhile about Fusion, just an older version of Layer.

    I multiplied the map over the Backlight, working fine.

    Thank you again

    Corrado

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