I am rendering a 3D model into a transparent PNG so that there is no background in the final render. All it contains is the fairly well detailed 3D model.

Now I want to include a shadow below the object as though it were sitting on a plane. I want the PNG to contain the model and a transparent shadow below it so that when I compose it over a variety of background images (which will be done on a website in markup) the shadow will appear to be cast on whatever I choose for the background image.

I've tried modeling a plane below with transparency, but then it doesn't seem to receive a shadow at all. What else could I try?

I am using 3DS Max, but I imagine that solutions exist that could be executed in various 3D software tools, though the details of implementation may be different.

So basically, what I am asking for help with is: how can I render a shadow below a 3D model such that it will be rendered as semi-transparent and without the ground plane in my final output?

  • I added a drop shadow with PS, but I consider that a workaround and not a real solution. I'm still hoping someone will offer a 3DS solution to this. The PS dropshadow isn't even close to a real shadow, but for our immediate purpose it will suffice.
    – Octopus
    Dec 15, 2017 at 21:37
  • 2
    I dont use 3DS Max but what you are looking for is a shadow catcher. You put a plane below your model and put a shadow catcher material on it and it will only render the shadow and not the plane. A quick google search brought me here. knowledge.autodesk.com/support/3ds-max/learn-explore/caas/…
    – icYou520
    Dec 20, 2017 at 23:24

1 Answer 1

  1. Create a plane where you want the shadow to be cast, like a floor.

  2. Right click, vray properties. In -matte properties, tick the “matte object” option, and set “alpha contribution” to -1.

In -direct light, tick the “shadows” and “Affect Alpha” options. When you render the image, save in PNG.

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