FX6 Render Passes: Ambient Final Gather

Overview

Using ShaderSpider and GlowWorm together, you can manipulate Poser's renders, using partial shaders to provide image enhancement or even more advanced rendering.

Example: Ambient Final Gather

A final gather is render that very realistically renders the way that light bounces between objects. For instance, a bright red object would faintly influence the color of other objects around it, tinging the other object with a faint red where the reflected light hit it.

With ambient objects, the effect is even more extreme. In a final gather situation, ambient objects act almost like light sources.

High level 3D software all have access to render engines, such as Mental Ray, that support such a feature. Poser doesn't, but you can fake it using GlowWorm and a Final Gather partial shader.

Partial Shader Setup

The Final Gather partial shader uses a Gather node attached to the Alternate_Diffuse input. The Alternate_Diffuse color is set to white. Gather nodes output black plus the reflected light color, so the only thing that Alternate_Diffuse will pick up is the reflected light. Alternate_Diffuse isn't premultiplied with other lighting, and we want to preserve ambient color, so that's why it was chosen.

Render Job Setup

The render job should use good quality render settings with a low sample rate (1.0 or less, depending on how much time you want the render to take) and raytracing enabled with at least 4 bounces.

The lower the Pixel Samples, the smoother the gather, but you don't want to go too low--the time goes up exponentially every time the sample rate is decreased. You can also smooth the image later in Photoshop, where you'll be compositing later anyways. Still, Pixel Samples between 0.6 and 1.0 is recommended.

You'll want to do at least 3 passes for the ambient final gather. You'll need a beauty pass, an ambient ("glow") pass and a specialized ambient pass to get the look of the above image.

Beauty Pass

This pass uses Diffuse and Show hair, and no partial shader. You may also want to do other passes, like specular and shadows, depending on your scene.

Ambient Pass

This pass uses Ambient and Show particles, but no partial shader. You need this pass to get your uncontaminated ambient color back.

Ambient Final Gather Pass

This pass should use Ambient and Show particles. You should set the partial shader to "Final Gather.fx6". This will make sure that you're getting the reflected glow only. You don't need to check "Alternate Diffuse"--partial shaders override the render pass's other settings.

Rendering

Here's fair warning: The AFG pass is going to be a slow, memory intensive render. Depending on the scene, you may want to take a quick nap while the AFG is performed.

Don't fret--partial shaders are not applied to Particles 2 figures, so the gather does not have to be performed for each particle in the scene.

Compositing

Open up your beauty pass, and paste the other two passes on top of it. Set the AFG pass's layer mode to "Linear Dodge" (aka "Add"). Photoshop's Smart Blur and Gaussian Blur should be applied to the AFG layer for best results.

Make a duplicate of the ambient layer and invert it. Set this layer to "Multiply" and place it above the AFG. This will make sure that your colors don't go wacky or way out of range.

Send the ambient layer to the very top, and set its layer mode to "Linear Dodge".

There you have it--a lovely glow!