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Volumetric light, Part 2

Author: semidieu

Tools Needed

  • Poser5

Introduction

This tutorial will cover the interactions of a volumetric light with a colored atmosphere. It will also cover multiple volumetric lights.

400-02262.jpg

This is the followup to Volumetric light, Part 1.

Step 1 - The colors

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Poser uses the RGB system color. You give the values for the RED component, the GREEN component and the BLUE component. These values range from 0 to 255.

Step 2 - White atmosphere with colored lights

In fact, “white” is the default value of the atmosphere. Everything works fine until you play with more two or more intersecting volumetric lights.

400-02282.jpg

Notice the blue cone behind the red cone doesn't appear blue, but magenta. And behind the green cone, the blue cone appears cyan.

Step 3 - Colored atmosphere with white light

At first glance, these pictures look very similar. But if you look more closely, you will notice that the highlights on the figure and on the ground are from the light color, independently of the color of the atmosphere.

400-02292.jpg

Step 4 - Colored atmosphere with colored light

The atmosphere diffuses the light it receives, but it can only diffuse light that is the same color as the particles that make up the atmosphere, the other colors being absorbed. This effect called is subtractive light.

With a white color atmosphere, the volumetric light will be the color of the light. There is no alteration (see Step 2): A “white” atmosphere means the Red, Green and Blue values are set to 255. These three colors combined make up the color white. Every light coming into this atmosphere will be completely diffused as no color will be subtracted.

In a colored atmosphere, let's say Red, the atmosphere can only diffuse the Red value of the lights (the other colors are absorbed):

  • a Red light will react as in the White atmosphere;
  • a Green or a Blue light won't be visible (only the volumetric part is invisible, not the highlights on physical objects)
  • a Cyan light (Red and Blue) will appear Red.

Here are some examples of what happens with different atmosphere colors. Notice the highlights produced by the spotlights: they show the original color of the volumetric light, which isn't always the same as that of the rendered volumetric light!

400-022a2.jpg

And here is another example:

400-022b2.jpg

Step 5 - Multiple volumetric lights

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Unlike the effect of the atmosphere, combining multiple lights is an additive operation: a red light over a blue light will combine as a cyan light.

This picture was rendered in Poser5, using three spotlights pointing to the ground: one red, one green and one blue. The atmosphere color is white.

The setting for the Volume_Density doesn't need to be changed no matter what the number of lights.

400-022d2.jpg

Finally, here is what happens with two volumetric lights, one red and one green. The Volume_Density is deliberately set quite high in order to show the different volume colors.

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Step 6 - Volumetric lights and special nodes (Advanced users)

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Finally, you can produce incredible volumetric light effects using some nodes (or light gel). This is not a tutorial on shaders: I'll only provide the BASIC settings and a final render (some postwork, only luminosity, contrast, etc. – nothing as been painted). The “light beam” is a volumetric light with shader nodes. I also set the Dist_Start and Dist_End value in order to stop the light at a specific point in space.

The light base settings:

400-02302.jpg

and the nodes settings:

400-02312.jpg

Thanks, as always, to my friend Mark for correcting my horrible English.