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Compositing with shadow pass tutorial

Requirements

This tutorial requires Indigo 3.6.19 or newer.

For this tutorial you will need a car model, standing on a single quad:

You will also need a high dynamic-range environment map (in .hdr or .exr format), plus a backplate image. (which are typically in .jpg format)


Preview of background plate from Moofe


Preview of HDR environment map from Moofe

The environment type should be set to Environment Map, and should be using the high dynamic range environment map mentioned.

Making the shadow pass

You will need to set the ground plane to be a shadow catcher material. To do this, first select the ground plane material with the Pick Material button. Then make the ground material be of Diffuse material type.

Then check the Shadow catcher checkbox at the bottom of the material options.

You may also be able to set the shadow catcher material option directly in your exporter.

Then change the render mode to Shadows:

This should produce a render like so:

For best results, you can make the car object invisible. You can do this by selecting the car object(s) with the Pick Object button, then checking the Invisible to camera checkbox, or by setting the Invisible to camera option for the object in your exporter.

This should produce a result like this:

Making the foreground car render

To make the foreground car render, the car object should be visible to the camera.
The ground object should be invisible to the camera - that is, it should have Invisible to camera checked: (Select the ground object with Pick Object to show these settings)

Now set the render mode to a normal rendering mode like Bidirectional path tracing.

Check the Foreground alpha checkbox. This will make only the car have non-zero alpha:

This should produce a render like this:

Compositing the layers together

We now have 3 layers that we want to composite together:

  • The background plate
  • The shadow pass
  • The foreground render

These layers can be easily composited together in a program such as Photoshop or GIMP:

The final result should look something like this:

Credits: Scene setup originally by hcpiter. Background plate and HDR are by Moofe.