Creating Shadows and Reflections In Combustion

In the following instructions, I refer to the leopard as the foreground layer.

In example #1, we see a basic composite without reflections or shadows. Notice the difference between this and example #2, which includes reflections and shadows. (Download the before and after movies above)


This is a 2 layer green screen composite (fig 1) of a leopard placed in an animated room.

Fig 1

Front

Matte Back

Animated Room

The goal is to create natural shadows and reflections using layers with specific attributes. This gives the artist more control with the shadows and reflections, as opposed to using operators like the shadow operator.

• Use the shadow operator.
• Create a shadow layer. This option offers the most control and the shadows are ray traced.
  We will use this option.

Fig 2



To create a shadow layer, open  2 layers in a 3-D composite in the “settings” tab turn on “shading,” “shadows” and “reflections” (fig2) and do the following:

• With your foreground layer, select and copy and paste the layer to duplicate it. Place the layer below the original layer and rename it “shadow layer”
• Now with the shadow layer, go to the layer tab and under options check on “invisible to camera” and “Cast shadows” (fig3).
• Next, in the shadow layer go to “surface” tab and adjust the opacity to about 50%.
• Parent the shadow layer to the foreground layer. (Fig3)

Fig 3

• On the background layer go to layer tab and make sure “receive shadows” is ON and “cast shadows” is OFF. (Fig4)

Fig 4

• Do the same for the foreground layer. Depending on where you place the shadows, you may have to turn receive shadows on or off.
• On the shadow layer, put a blur operator on the layer and increase the amount of blur to add softness.

Now you have a ray traced shadow that you can place anywhere!

Add a light object, move it around and notice its effect on the shadow layer.
Scale and place the shadow layer accordingly.

• With your foreground layer, select it and copy and paste to duplicate the layer.
• Place the layer below the original layer and rename it “reflection layer”.
• In the reflection layer, go to the layer tab and shut OFF all options.
• Now go to the surface tab and change the opacity to a small amount try 25%.
  (Later on you can experiment with the transfer modes in this menu)
• Go to the transform tab, and change the rotation Y and Z values to 180.
  This is a generic flip depending, on what you are trying to achieve with the reflection,
  You may adjust these values accordingly.
• Place the layer so it reflecting from the floor (fig5)

Fig 5.

• Parent the reflection layer to the original layer. (Fig5)

Now go back to the settings tab and turn the reflections tab OFF. Notice it doesn't affect our reflection. This is because the reflections are created from the layer itself. What this setting does is create reflections from one layer to another.

Depending on what you are doing, you may want to turn this off to save CPU power. You can also experiment with the transfer modes in the “surface” tabs to change the type of the reflection.

At this point, you are ready to light your composite. For me, I like to think in terms of basic television lighting…ex. key, fill spots etc. But that's another lesson in itself. For this piece, I have a null as a target for the spot light. And I used a basic fill light.

• When you are creating shadow and reflection layers, all you are doing is modifying the layer and surface attributes of the individual layers.
• Always start in the settings tab with all 3 attributes on!
• Don't forget to parent to your primary layers.
• Experiment with lighting and above all, have FUN!

---Mike Harper

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You can learn more about this and other techniques by joining in the discussions in the Discreet Combustion forum at Creativecow.

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